2,113 results on '"Qian, D"'
Search Results
2. The Atherogenic Index of Plasma Predicts Carotid in-Stent Restenosis: Development and Validation of a Nomogram
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Zhou Y, Ma Y, Qian D, Zhou Z, Li B, and Chai E
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atherogenic index of plasma ,carotid stenosis ,carotid in-stent restenosis ,neurointervention ,nomogram ,Medicine (General) ,R5-920 - Abstract
Yu Zhou,1– 3,* Yong Ma,2– 4,* Dongliang Qian,2,3,* Zhou Zhou,5,6,* Bin Li,2,3,* Erqing Chai1– 3 1First Clinical Medical College, Lanzhou University, Lanzhou, People’s Republic of China; 2Cerebrovascular Disease Center, Gansu Provincial Hospital, Lanzhou, People’s Republic of China; 3Key Laboratory of Cerebrovascular Diseases, Lanzhou, People’s Republic of China; 4Clinical Medicine College, Ningxia Medical University, Yinchuan, People’s Republic of China; 5First Teaching Hospital of Tianjin University of Traditional Chinese Medicine, Tianjin, People’s Republic of China; 6National Clinical Research Center for Chinese Medicine Acupuncture and Moxibustion, Tianjin, People’s Republic of China*These authors contributed equally to this workCorrespondence: Erqing Chai, First Clinical Medical College, Lanzhou University, No. 204, Donggang West Road, Chengguan District, Lanzhou City, 730000, People’s Republic of China, Tel +86 13893439044, Email ldyy_chaieq@lzu.edu.cnPurpose: To explore the predictive value of atherogenic index of plasma(AIP) for carotid in-stent restenosis(ISR).Methods: Patients who underwent carotid artery stenting (CAS) in hospital from January 2016 to January 2021 were retrospectively enrolled. They were randomly divided into training and validation sets. Based on the results of carotid digital subtraction angiography (DSA) during the follow-up period, the patients were divided into ISR group and non-ISR group. The differences of AIP and lipid levels between the two groups were compared. The independent risk factors of ISR and the predictive value of AIP for ISR were analyzed. A nomogram was developed based on the independent risk factors, and the receiver operating characteristic (ROC) curve, the calibration curve and the decision curve analysis were conducted to assess the predictive ability and clinical practicability of the nomogram in both the training set and validation sets.Results: A total of 361 patients were enrolled, including 98 in the ISR group and 263 in the non-ISR group. In the training set, AIP was significantly higher in the ISR group than in the non-ISR group (P < 0.05) and was independently associated with ISR (OR= 10.912, 95% CI: 2.520– 47.248). When AIP was 0.10, it had the highest predictive value for ISR, with a sensitivity of 72. 1% and a specificity of 75.0%. Additionally, hypertension, residual stenosis, symptomatic stenosis and Hcy were also independent risk factors for ISR. The nomogram showed good discrimination performance and clinical practicability in both the training set (AUC = 0.827) and the validation set (AUC = 0.880).Conclusion: AIP was an independent risk factor for ISR and was closely related to ISR. The nomogram developed by AIP and other variables had good predictive ability and clinical practicability for ISR.Keywords: atherogenic index of plasma, carotid stenosis, carotid in-stent restenosis, neurointervention, nomogram
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- 2024
3. A flux tunable superconducting quantum circuit based on Weyl semimetal MoTe2
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Chiu, K. L., Qian, D. G., Qiu, J. W., Liu, W. Y., Tan, D., Mosallanejad, V., Liu, S., Zhang, Z. T., Zhao, Y., and Yu, D. P.
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Quantum Physics ,Condensed Matter - Materials Science - Abstract
Weyl semimetals for their exotic topological properties have drawn considerable attention in many research fields. When in combination with s-wave superconductors, the supercurrent can be carried by their topological surface channels, forming junctions mimic the behavior of Majorana bound states. Here, we present a transmon-like superconducting quantum intereference device (SQUID) consists of lateral junctions made of Weyl semimetal Td-MoTe2 and superconducting leads niobium nitride (NbN). The SQUID is coupled to a readout cavity made of molybdenum rhenium (MoRe), whose response at high power reveal the existence of the constituting Josephson junctions (JJs). The loop geometry of the circuit allows the resonant frequency of the readout cavity to be tuned by the magnetic flux. We demonstrate a JJ made of MoTe2 and a flux-tunable transmon-like circuit based on Weyl materials. Our study provides a platform to utilize topological materials in SQUID-based quantum circuits for potential applications in quantum information processing.
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- 2020
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4. Social Support Mediates the Relationship Between Coping Styles and the Mental Health of Medical Students
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Dai P, Yi G, Qian D, Wu Z, Fu M, and Peng H
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mediating effect ,structural equation model ,questionnaire investigation ,psychological wellbeing ,Psychology ,BF1-990 ,Industrial psychology ,HF5548.7-5548.85 - Abstract
Peilin Dai,1,2,* Guoguo Yi,3,4,* Dandan Qian,5,* Zhe Wu,2 Min Fu,6 Hui Peng1 1School of Nursing, Hunan University of Medicine, Huaihua, Hunan, People’s Republic of China; 2The Second School of Clinical Medicine, Southern Medical University, Guangzhou, People’s Republic of China; 3Department of Ophthalmology, The Sixth Affiliated Hospital, Sun-Yat-sen University, Guangzhou, People’s Republic of China; 4Biomedical Innovation Center, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, People’s Republic of China; 5Department of Clinical Skills Training Center, Zhujiang Hospital, Southern Medical University, Guangzhou, People’s Republic of China; 6Department of Ophthalmology, Zhujiang Hospital of Southern Medical University, Guangzhou, People’s Republic of China*These authors contributed equally to this workCorrespondence: Min Fu, Department of Ophthalmology, Zhujiang Hospital of Southern Medical University, No. 253, Industrial Avenue Middle, Haizhu, Guangzhou, People’s Republic of China, Tel +86 18665621066, Email min_fu1212@163.com Hui Peng, School of Nursing, Hunan University of Medicine, No. 492, Jinxi South Road, Huaihua, Hunan, People’s Republic of China, Email pengh533@163.comPurpose: This study aimed to explore the impact that coping styles and social support have on the mental health of medical students by constructing a corresponding structural situation model that reveals the complex relationship between these three factors. In doing so, it seeks to help medication students better manage mental health problems.Patients and Methods: The online study was conducted between March 6, 2021 and May 6, 2021. A total of 318 participants from multiple medical schools were involved. The general information questionnaire, simple coping style questionnaire (SCSQ), perceived social support scale (PSSS) and symptom checklist 90 (SCL-90) were used to collect relevant information from the subjects by snowball sampling. An independent t-test, ANOVA, Pearson correlation coefficient analysis, and intermediary effect analysis were all used to analyze the relevant data and construct the structural equation model.Results: There was a significant difference in SCL-90 between medical students and national college students (1.78± 0.70, P < 0.001), and the positive rate of mental health status was as high as 40.3%. Sleep quality, regular diet, and positive coping style were positively correlated with mental health (P < 0.01), while negative coping styles and total scores of coping style as well as family, friends, and other sources of social support and total scores of social support were negatively correlated with mental health problems (P < 0.01). Positive and negative coping styles have an impact on mental health through the mediating effect of between social support and coping styles, as well as in the direct pathway.Conclusion: The mental health status of medical students was significantly poor. Medical schools should thus pay close attention to the mental health status of students and encourage them to develop healthy living habits, optimize coping styles, and establish stable sources of social support to improve their psychological wellbeing.Keywords: mediating effect, structural equation model, questionnaire investigation, psychological wellbeing
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- 2023
5. Metabolomics Combined with Network Pharmacology-Based Strategy to Reveal the Underlying Mechanism of Zhenhuang Submicron Emulsion in Treating Oropharyngeal Mucositis Complications of Radiation Therapy for Head and Neck Cancer
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Chen W, Li C, Jin D, Shi Y, Zhang M, Bo M, Qian D, Wang M, and Li G
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metabolomics ,network pharmacology ,mucositis ,traditional chinese medicine ,head and neck tumors ,Therapeutics. Pharmacology ,RM1-950 - Abstract
Wei Chen,1,* Chunyu Li,1,* Dujia Jin,2 Yafei Shi,1 Mingyu Zhang,1 Mingming Bo,1 Di Qian,1 Mengyang Wang,1 Guohui Li1 1Department of Pharmacy, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People’s Republic of China; 2Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People’s Republic of China*These authors contributed equally to this workCorrespondence: Guohui Li, Department of Pharmacy, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People’s Republic of China, Tel +861087788573, Email lgh0603@cicams.ac.cnIntroduction: Head and neck tumors account for more than 6% of all cancers. The primary treatment for tumors of the head and neck is radiation therapy, which can induce oropharyngeal mucositis as a side effect. At present, there is no widely available therapeutic for the treatment of oropharyngeal mucositis in clinical practice. Based on the traditional prescription Liushen Wan, the pathogenesis and pathology, we developed a new Chinese medicine prescription and made Zhenhuang submicron emulsion (ZHSE) spray, which has an efficacious therapeutic effect for oropharyngeal mucositis. However, its mechanism is unclear.Methods: This research explored the mechanism behind the modulatory effects of ZHSE by a strategy of metabolomics and network pharmacology. Multivariate data analyses, including unsupervised principal component analysis (PCA) and supervised orthogonal partial least squares discriminant analysis (OPLS-DA), were performed. Potential biomarkers were identified depending on the mass-charge ratio of the selected compound. Statistical and pathway enrichment analysis was performed in the KEGG pathway database. Network pharmacology combining metabolomic analyses was conducted to illustrate the key targets and pathways.Results: Critical metabolic pathways were investigated, 56f biomarkers were enriched and key metabolites such as linoleic acid, 9,10-epoxyoctadecenoic acid, acetoacetic acid and citric acid were identified. A complex network of “compound-target-potential metabolite” interactions was drawn to illuminate the regulation of chemical constituents on key metabolites. These findings manifest that ZHSE regulates endogenous metabolite disorders during the treatment of oropharyngeal mucositis by various constituents, interacting with multiple targets associated with inflammation and pain.Conclusion: In this work, we determined several critical biomarkers and metabolic pathways and identified the possible regulatory mechanism by which ZHSE functions in the treatment of oropharyngeal mucositis. This study provides a new perspective on integrating metabolomics and network pharmacology for exploring improved therapy for head and neck tumors based on the traditional classic prescription of LSW.Keywords: metabolomics, network pharmacology, mucositis, traditional Chinese medicine, head and neck tumors
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- 2022
6. POS0420 TEMPORAL ASSOCIATION BETWEEN BREAST CANCER AND SYSTEMIC SCLEROSIS: A CROSS-SECTIONAL ANALYSIS IN AN URBAN INSTITUTION
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Feng, J., primary, He, C., additional, Dobrowolski, C., additional, Verma, H., additional, Vasoya, R., additional, Qian, D., additional, Olumuyide, E., additional, Leong, A., additional, Menand, J., additional, Bastos Silva, M., additional, Courant, V., additional, and Lutgen, S., additional
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- 2024
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7. Deep Learning–Based Facial and Skeletal Transformations for Surgical Planning
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Bao, J., primary, Zhang, X., additional, Xiang, S., additional, Liu, H., additional, Cheng, M., additional, Yang, Y., additional, Huang, X., additional, Xiang, W., additional, Cui, W., additional, Lai, H.C., additional, Huang, S., additional, Wang, Y., additional, Qian, D., additional, and Yu, H., additional
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- 2024
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8. Magnetic Properties of the low dimensional BaM$_2$Si$_2$O$_7$(M= Cu, Co, Mn) system
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Wang, G. H., Xu, C. Y., Cao, H. B., Hong, T., Huang, Q., Ren, Q. Y., Xu, J. Q., Zhou, H. D., Luo, W. D., Qian, D., and Ma, J.
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Condensed Matter - Strongly Correlated Electrons - Abstract
We performed susceptibility, magnetization, specific heat, and single crystal neutron diffraction measurements on single crystalline BaMn$_2$Si$_2$O$_7$. Based on the results, we revisited its spin structure with a more accurate solution and constructed a magnetic phase diagram with applied field along the $b$-axis, which contains a spin flop transition around 6 T. We also used susceptibility, magnetization, and specific heat results confirmed the ferrimagnetic-like magnetism in polycrystalline BaCo$_2$Si$_2$O$_7$. Furthermore, we performed LSDA + U calculations for the BaM$_2$Si$_2$O$_7$ (M = Cu, Co, and Mn) system. Our discussions based on the comparison among the obtained magnetic exchange interactions suggest the different structures and electronic configurations are the reasons for the different magnetic properties among the system members.
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- 2018
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9. Magnetoelectric and Raman spectroscopic studies of single-crystalline MnCr2O4
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Lin, G. T., Wang, Y. Q., Luo, X., Ma, J., Zhuang, H. L., Qian, D., Yin, L. H., Chen, F. C., Yan, J., Zhang, R. R., Zhang, S. L., Tong, W., Song, W. H., Tong, P., Zhu, X. B., and Sun, Y. P.
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Condensed Matter - Materials Science - Abstract
MnCr2O4 that exhibits spin frustration and complex spiral spin order is of great interest from both fundamental as well as application-oriented perspectives. Unlike CoCr2O4 whose ground state presents the coexistence of commensurate spiral spin order (CSSO) and ferroelectric order, MnCr2O4 shows no multiferroicity. One reason is that the spiral spin order is highly sensitive to the oxygen concentration in MnCr2O4. Here, we have successfully grown high-quality single-crystalline MnCr2O4 by the chemical vapor transport method. We observe a new first-order magnetic transition from the incommensurate spiral spin order (ICSSO) at 19.4 K to the CSSO at 17.4 K. This magnetic transition is verified by magnetization, specific heat, and magnetoelectric measurements, which also confirm that the ground state exhibits the coexistence of the CSSO and magnetoelectricity below 17.4 K. Interestingly, the temperature evolution of Raman spectra between 5.4 and 300 K suggests that the structure remains the same. We also find that the phase-transition temperature of the CSSO decreases as applied magnetic field increases up to 45 kOe., Comment: Accepted by Phys. Rev. B
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- 2018
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10. Electronic structure of Ba(Zn0.875Mn0.125)2As2 studied by angle-resolved photoemission spectroscopy
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Zhu, Fengfeng, Jiang, W. X., Li, P., Wang, Z. Q., Man, H. Y., Li, Y. Y., Liu, Canhua, Guan, D. D., Jia, J. F., Ning, F. L., Luo, Weidong, and Qian, D.
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Condensed Matter - Materials Science - Abstract
Electronic structure of single crystalline Ba(Zn$_{0.875}$Mn$_{0.125}$)$_{2}$As$_{2}$, parent compound of the recently founded high-temperature ferromagnetic semiconductor, was studied by high-resolution photoemission spectroscopy (ARPES). Through systematically photon energy and polarization dependent measurements, the energy bands along the out-of-plane and in-plane directions were experimentally determined. Except the localized states of Mn, the measured band dispersions agree very well with the first-principle calculations of undoped BaZn$_{2}$As$_{2}$. A new feature related to Mn 3d states was identified at the binding energies of about -1.6 eV besides the previously observed feature at about -3.3 eV. We suggest that the hybridization between Mn and As orbitals strongly enhanced the density of states around -1.6 eV. Although our resolution is much better compared with previous soft X-ray photoemission experiments, no clear hybridization gap between Mn 3d states and the valence bands proposed by previous model calculations was detected.
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- 2016
11. Antiferromagnetic order in epitaxial FeSe films on SrTiO3
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Zhou, Y., Miao, L., Wang, P., Zhu, F. F., Jiang, W. X., Jiang, S. W., Zhang, Y., Ding, H. F., Zheng, H., Jia, J. F., Qian, D., and Wu, D.
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Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
Single monolayer FeSe film grown on Nb-doped SrTiO$_3$(001) substrate shows the highest superconducting transition temperature (T$_C$ $\sim$ 100 K) among the iron-based superconductors (iron-pnictide), while T$_C$ of bulk FeSe is only $\sim$ 8 K. Antiferromagnetic spin fluctuations were believed to be crucial in iron-pnictides, which has inspired several proposals to understand the FeSe/SrTiO$_3$ system. Although bulk FeSe does not show the antiferromagnetic order, calculations suggest that the parent FeSe/SrTiO$_3$ films are AFM. Experimentally, due to lacking of direct probe, the magnetic state of FeSe/SrTiO$_3$ films remains mysterious. Here, we report the direct evidences of the antiferromagnetic order in the parent FeSe/SrTiO$_3$ films by the magnetic exchange bias effect measurements. The phase transition temperature is $\geq$ 140 K for single monolayer film. The AFM order disappears after electron doping.
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- 2016
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12. 1O Uncovering new immunotherapy targets with machine learning and ex vivo validation
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Augustine, M., primary, Nene, N. Rocha, additional, Thakkar, K., additional, Qian, D., additional, Fitzsimons, E., additional, Pinder, C., additional, Fu, H., additional, Ligammari, L., additional, Simpson, B., additional, Watkins, C., additional, Swanton, C., additional, and Litchfield, K.R., additional
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- 2024
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13. A novel design of low carbon footprint Ultra-High Performance Concrete (UHPC) based on full scale recycling of gold tailings
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Wang, J.N., Yu, R., Xu, W.Y., Hu, C.Y., Shui, Z.H., Qian, D., Leng, Y., Liu, K.N., Hou, D.S., and Wang, X.P.
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- 2021
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14. Hardness and microstructural inhomogeneity at the epitaxial interface of laser 3D-printed Ni-based superalloy
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Qian, D, Zhang, A, Zhu, J, Li, Y, Zhu, W, Qi, B, Tamura, N, Li, D, Song, Z, and Chen, K
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Applied Physics ,Engineering ,Physical Sciences ,Technology - Abstract
In this letter, microstructural and mechanical inhomogeneities, a great concern for single crystal Ni-based superalloys repaired by laser assisted 3D printing, have been probed near the epitaxial interface. Nanoindentation tests show the hardness to be uniformly lower in the bulk of the substrate and constantly higher in the epitaxial cladding layer. A gradient of hardness through the heat affected zone is also observed, resulting from an increase in dislocation density, as indicated by the broadening of the synchrotron X-ray Laue microdiffraction reflections. The hardening mechanism of the cladding region, on the other hand, is shown to originate not only from high dislocation density but also and more importantly from the fine γ/γ′ microstructure.
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- 2016
15. 142P Identifying novel immunotherapy targets using machine learning and ex vivo validation
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Augustine, M., primary, Nene, N. Rocha, additional, Thakkar, K., additional, Qian, D., additional, Fitzsimons, E., additional, Simpson, B., additional, Watkins, C., additional, Swanton, C., additional, and Litchfield, K.R., additional
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- 2023
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16. 41P Contrasting drivers of response to immunotherapy across solid tumour types: Results from analysis of >2500 cases
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Qian, D., primary, Thakkar, K., additional, Castro, A., additional, Swanton, C., additional, and Litchfield, K.R., additional
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- 2023
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17. EP08.02-37 Definitive Hypofractionated Radiation Therapy with or without Immunotherapy for Stage IIb-III NSCLC: An Institutional Experience
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Hopkins, B., primary, Qian, D., additional, Kesarwala, A., additional, Stokes, B., additional, Shelton, J., additional, Steuer, C., additional, Carlisle, J., additional, Leal, T., additional, Ramalingam, S., additional, Higgins, K., additional, and Tian, S., additional
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- 2023
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18. MA18.03 Preliminary Safety and Treatment Data of A Phase 3 Trial: Hypofractionated vs Conventional Fractionated Concurrent Chemoradiation for LS-SCLC
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Bi, N., primary, Zhang, T., additional, Hu, X., additional, Zhang, L., additional, Zhang, J., additional, Cao, J., additional, E, M., additional, Ge, H., additional, Zhu, X., additional, Zhao, L., additional, Jiang, W., additional, Qian, D., additional, Shen, W., additional, Wang, Y., additional, Ran, J., additional, Hu, C., additional, Chen, M., additional, and Wang, L., additional
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- 2023
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19. Neoadjuvant Chemoradiotherapy Combined with Nimotuzumab and Camrelizumab in Initially Inoperable Patients with Locally Advanced Esophageal Cancer: A Prospective, One-Arm, Phase II Study
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He, Y., primary, Hu, Q.A., additional, Li, X.P., additional, and Qian, D., additional
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- 2023
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20. Spin Order by Quantum Frustration in Triangular Lattice Mott Insulator NaCrO2 : A Neutron Scattering Study
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Hsieh, D., Qian, D., Berger, R. F., Liu, C., Ueland, B., Schiffer, P., Huang, Q., Cava, R. J., Lynn, J. W., and Hasan, M. Z.
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Condensed Matter - Strongly Correlated Electrons - Abstract
We report high resolution neutron scattering measurements on the triangular lattice Mott insulator Na$_x$CrO$_2$ ($x$=1) which has recently been shown to exhibit an unusually broad fluctuating crossover regime extending far below the onset of spin freezing ($T_c\sim$41K). Our results show that below some crossover temperature ($T\sim0.75T_c$) a small incommensuration develops which helps resolve the spin frustration and drives three-dimensional magnetic order supporting coherent spin wave modes. This incommensuration assisted dimensional crossover suggests that inter-layer frustration is responsible for stabilizing the rare 2D correlated phase above 0.75$T_c$. In contrast to the host compound of 2D cobaltate superconductor such as Na$_x$CoO$_2$ ($\xi_c>50$\AA), no magnetic long-range order is observed down to 1.5K ($\xi_c<16$\AA)., Comment: 5 pages, 4 figures
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- 2014
21. A synchrotron study of defect and strain inhomogeneity in laser-assisted three-dimensionally-printed Ni-based superalloy
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Li, Y, Qian, D, Xue, J, Wan, J, Zhang, A, Tamura, N, Song, Z, and Chen, K
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Applied Physics ,Engineering ,Physical Sciences ,Technology - Abstract
Synchrotron X-ray microdiffraction was employed to investigate the inhomogeneous distribution of defect and residual strain in the transitional region between the dendritic and stray grains in a laser-assisted 3D printed Ni-based superalloy. The dendritic region was found to be under tensile strain transversely to the primary dendrite arm directions. The dendrite edges, where high level of strains and geometrically necessary dislocations were detected, were discerned as low angle grain boundaries. High angle grain boundaries were observed in the stray grain region, and the orientation of the strain tensor in this region varied dramatically at the micron scale, in contrast with the more or less homogeneous distribution in the dendritic region.
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- 2015
22. A topological crystalline insulator (TCI) phase via topological phase transition and crystalline mirror symmetry
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Xu, Su-Yang, Liu, Chang, Alidoust, Nasser, Neupane, M, Qian, D., Belopolski, I., Denlinger, J. D., Wang, Y. J., Lin, H., Wray, L. A., Landolt, G., Slomski, B., Dil, J. H., Marcinkova, A., Morosan, E., Gibson, Q., Sankar, R., Chou, F. C., Cava, R. J., Bansil, A., and Hasan, M. Z.
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
A Z2 topological insulator protected by time-reversal symmetry is realized via spin-orbit interaction driven band inversion. For example, the topological phase in the Bi-Sb system is due to an odd number of band inversions. A related spin-orbit system, the (Pb/Sn)Te class, has been known to contain an even number of inversions based on band theory. Here we experimentally investigate the possibility of a mirror symmetry protected topological crystalline insulator phase in the (Pb/Sn)Te class of materials which has been theoretically predicted to exist in its non-alloyed version. Our experimental results show that at a finite-Pb composition above the topological inversion phase transition, the surface exhibits even number of spin-polarized Dirac cone states (as opposed to odd as observed in Bi-Sb alloy or Bi2Se3) revealing mirror protected topological order distinct from that observed in Bi-Sb or Bi2Se3. Our observation of the spin-polarized Dirac surface states in the inverted (Pb/Sn)Te and their absence in the non-inverted compounds related via a topological phase transition (spin-orbit induced band inversion type) provide the experimental groundwork for opening the research on novel topological order in future quantum devices., Comment: 45 pages, 17 Figures, Earlier observation reported at http://xxx.lanl.gov/abs/1206.2088 (11th June, 2012); Expanded ver.(17 Figs) accepted for publication (in press) in Nature Communications (2012)
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- 2012
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23. Deviating band symmetries and many-body interactions in a model hole doped iron pnictide superconductor
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Wray, L. A., Thomale, R., Platt, C., Hsieh, D., Qian, D., Chen, G. F., Luo, J. L., Wang, N. L., and Hasan, M. Z.
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Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present a polarization resolved study of the low energy band structure in the optimally doped iron pnictide superconductor Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ (T$_c$=37K) using angle resolved photoemission spectroscopy. Polarization-contrasted measurements are used to identify and trace all three low energy hole-like bands predicted by local density approximation (LDA) calculations. The photoemitted electrons reveal an inconsistency with LDA-predicted symmetries along the $\Gamma$-X high symmetry momentum axis, due to unexpectedly strong rotational anisotropy in electron kinetics. We evaluate many-body effects such as Mott-Hubbard interactions that are likely to underlie the anomaly, and discuss how the observed deviations from LDA band structure affect the energetics of iron pnictide Cooper pairing in the hole doped regime., Comment: 7.1 pages, 5 figures. Symmetry analysis revised. Accepted for publication in Phys. Rev. B
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- 2012
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24. Observation of Topological Crystalline Insulator phase in the lead tin chalcogenide Pb1-xSnxTe material class
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Xu, Su-Yang, Liu, Chang, Alidoust, N., Qian, D., Neupane, M., Denlinger, J. D., Wang, Y. J., Wray, L. A., Cava, R. J., Lin, H., Marcinkova, A., Morosan, E., Bansil, A., and Hasan, M. Z.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
We perform systematic angle-resolved photoemission spectroscopic measurements on the lead tin telluride Pb1-xSnxTe pseudobinary alloy system. We show that the (001) crystalline surface, which is a crystalline surface symmetric about the (110) mirror planes of the Pb1-xSnxTe crystal, pos- sesses four metallic surface states within its surface Brillouin zone. Our systematic Fermi surface and band topology measurements show that the observed Dirac-like surface states lie on the symmetric momentum-space cuts. We further show that upon going to higher electron binding energies, the surface states' isoenergetic countours in close vicinity of each X point are observed to hybridize with each other, leading to a Fermi surface fractionalization and the Lifshitz transition. In addition, systematic incident photon energy dependent measurements are performed, which enable us to un- ambiguously identify the surface states from the bulk bands. These systematic measurements of the surface and bulk electronic structure on Pb1-xSnxTe, supported by our first principles calculation results, for the first time, show that the Pb1-xSnxTe system belongs to the topological crystalline insulator phase due to the four band inversions at the L points in its Brillouin zone, which has been recently theoretically predicted., Comment: 4 pages, 4 Figures, Submitted May '12
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- 2012
25. How Virtual Reality Can Increase Effectiveness of Prosocial Advertising: Put Yourself in the Donees Shoes: The Effect of Virtual Reality on Charitable Donations
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Li, O., Pan, Z., Qiu, H., and Qian, D.
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- 2024
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26. Topological Phase Transition and Texture Inversion in a Tunable Topological Insulator
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Xu, Su-Yang, Xia, Y., Wray, L. A., Qian, D., Jia, Shuang, Dil, J. H., Meier, F., Osterwalder, J., Slomski, B., Lin, H., Cava, R. J., and Hasan, M. Z.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter - Strongly Correlated Electrons - Abstract
The recently discovered three dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice via odd number of band inversions, driving the system through a topological quantum phase transition. By directly measuring the topological invariants (for the method to directly measure Fu-Kane {$\nu_0$}, see Hsieh \textit{et.al.,} Science 323, 919 (2009) at http://www.sciencemag.org/content/323/5916/919.abstract) we report the observation of a phase transition in a tunable spin-orbit system BiTl(S{1-d}Se{d})2 (which is an analog of the most studied topological insulator Bi2Se3, see Xia \textit{et.al.,} Nature Phys. 5, 398 (2009) at http://www.nature.com/nphys/journal/v5/n6/full/nphys1294.html and Spin-Momentum locking at http://www.nature.com/nature/journal/v460/n7259/full/nature08234.html) where the topological insulator state formation is visualized for the first time. In the topological state, vortex-like polarization states are observed to exhibit 3D vectorial textures, which collectively feature a chirality transition of its topological spin-textures as the spin-momentum locked (Z2 topologically ordered) electrons on the surface go through the zero carrier density point. Such phase transition and texture chirality inversion can be the physical basis for observing \textit{fractional charge} (e/2) and other related fractional topological phenomena., Comment: 13 pages, 4 Figures, Accepted for publication in Science (published at ScienceExpress on 31 March, 2011)
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- 2011
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27. Direct observation of spin-polarized surface states in the parent compound of topological insulator Bi-Sb using spin-resolved-ARPES in a 3D Mott-polarimetry spin mode
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Hsieh, D., Xia, Y., Wray, L., Qian, D., Dil, J. H., Meier, F., Patthey, L., Osterwalder, J., Bihlmayer, G., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Disordered Systems and Neural Networks ,Quantum Physics - Abstract
We report high-resolution spin-resolved photoemission spectroscopy (Spin-ARPES) measurements on the parent compound Sb of the first discovered 3D topological insulator Bi{1-x}Sb{x} [D. Hsieh et al., Nature 452, 970 (2008) Submitted 2007]. By modulating the incident photon energy, we are able to map both the bulk and (111) surface band structure, from which we directly demonstrate that the surface bands are spin polarized by the spin-orbit interaction and connect the bulk valence and conduction bands in a topologically non-trivial way. A unique asymmetric Dirac surface state gives rise to a $k$-splitting of its spin polarized electronic channels. These results complement our previously published works on this materials class and re-confirm our discovery of first bulk (3D) topological insulator - topological order in bulk solids. [Invited article for NJP-IOP Focus issue on "Topological Insulators"], Comment: Invited article for NJP-IOP Focus issue on "Topological Insulators", Experimental discovery of 3D topological insulators (topological order in bulk solids) reported at KITP (2007) Conference Proceeding at http://online.itp.ucsb.edu/online/motterials07/hasan/ (2007)
- Published
- 2011
28. The development of ferromagnetism in the doped topological insulator Bi2-xMnxTe3
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Hor, Y. S., Roushan, P., Beidenkopf, H., Seo, J., Qu, D., Checkelsky, J. G., Wray, L. A., Xia, Y., Xu, S. -Y., Qian, D., Hasan, M. Z., Ong, N. P., Yazdani, A., and Cava, R. J.
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
The development of ferromagnetism in Mn-doped Bi2Te3 is characterized through measurements on a series of single crystals with different Mn content. Scanning tunneling microscopy analysis shows that the Mn substitutes on the Bi sites, forming compounds of the type Bi2-xMnxTe3, and that the Mn substitutions are randomly distributed, not clustered. Mn doping first gives rise to local magnetic moments with Curie-like behavior, but by the compositions Bi1.96Mn0.04Te3 and Bi1.91Mn0.09Te3 a second order ferromagnetic transition is observed, with Tc ~ 9-12 K. The easy axis of magnetization in the ferromagnetic phase is perpendicular to the Bi2Te3 basal plane. Thermoelectric power and Hall effect measurements show that the Mn-doped Bi2Te3 crystals are p-type. Angle resolved photoemission spectroscopy measurements show that the topological surface states that are present in pristine Bi2Te3 are also present in ferromagnetic Mn-doped Bi2-xMnxTe3, and that the dispersion relations of the surface states are changed in a subtle fashion.
- Published
- 2010
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29. First observation of Spin-Momentum Helical Locking in Bi2Se3 and Bi2Te3, demonstration of Topological-Order at 300K and a realization of topological-transport-regime
- Author
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Hsieh, D., Xia, Y., Qian, D., Wray, L., Dil, J. H., Meier, F., Osterwalder, J., Patthey, L., Checkelsky, J. G., Ong, N. P., Fedorov, A. V., Lin, H., Bansil, A., Grauer, D., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Strongly Correlated Electrons - Abstract
Both the theoretical and experimental discovery of single-Dirac-cone topological-insulator-class was reported at arXiv:0812.2078 (2008) [Y. Xia et.al., Nature Physics 5, 398-402 (2009) http://www.nature.com/nphys/journal/v5/n6/full/nphys1294.html]. Here we report the first observation of Spin-Momentum Helical Locking and Spin-Vortex structures in Bi2Se3 and Bi2Te3, demonstrate the existence of Topological-Order at 300K and report a material realization of topological-transport-regime for helical Dirac fermions. Our results reveal a one-to-one spin-momentum locked Dirac structure in Bi2Se3 and Bi2Te3 that is nearly 100% spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers' point and can be driven to the long-sought topological-transport-regime. The observed topological nodal Dirac ground state is found to be protected even up to room temperature (300 K). Our results pave the way for future transport based studies of topological insulators, and possible room temperature applications of protected spin-polarized edge channels we observe with spin-ARPES in spintronic technology. All of these new results are made possible due to the Spin-resolved-ARPES (Mott polarimetric) technique [http://www.nature.com/nature/journal/v460/n7259/full/nature08234.html ] ., Comment: 17 pages, 4 Figures, Published nature-Online in July-2009, Submitted to NATURE in April-2009
- Published
- 2010
- Full Text
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30. Direct observation of spin-polarized surface states in the parent compound of a topological insulator using high-resolution spin-resolved-ARPES spectroscopy in a Mott-polarimetry mode
- Author
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Hsieh, D., Wray, L. A., Qian, D., Xia, Y., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Other Condensed Matter - Abstract
We report high-resolution spin-resolved photoemission spectroscopy (Spin-ARPES) measurements on the parent compound Sb of the recently discovered 3D topological insulator Bi1-xSbx [D. Hsieh et al., Nature 452, 970 (2008)]. By modulating the incident photon energy, we are able to map both the bulk and (111) surface band structure, from which we directly demonstrate that the surface bands are spin polarized by the spin-orbit interaction and connect the bulk valence and conduction bands in a topologically non-trivial way. A unique asymmetric Dirac surface state gives rise to a k-splitting of its spin polarized electronic channels. These results complement our previously published works on this materials class and re-confirm our discovery of topological insulator states in the Bi-Sb series., Comment: 5 pages, 5 figures
- Published
- 2010
31. Observation of intertwined Fermi surface topology, orbital parity symmetries and electronic interactions in iron arsenide superconductors
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Wray, L. A., Hsieh, D., Xia, Y., Xu, S. -Y., Qian, D., Chen, G. F., Luo, J. L., Wang, N. L., and Hasan, M. Z.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Superconductivity - Abstract
We present a polarization and topology resolved study of the low energy band structure in optimally doped superconducting Ba0.6K0.4Fe2As2 using angle resolved photoemission spectroscopy. Polarization-contrasted measurements allow us to identify and trace all low energy bands expected in models, revealing unexpected symmetry breaking and a surprisingly intertwined Fermi surface topology of hole-like bands near the Brillouin zone center. Band structure correlations across the Gamma-M spin fluctuation wavevector are compared with the superconducting gap anisotropy which suggest a partial scenario for spin-mediated interband instability contributing to superconductivity in the hole doped regime., Comment: 5 pages, 4 Figures (low-res), Submitted December 2009
- Published
- 2009
32. Observation of unconventional band topology in a superconducting doped topological insulator, Cux-Bi2Se3: Topological Superconductor or non-Abelian superconductor?
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Wray, L., Xu, S., Xiong, J., Xia, Y., Qian, D., Lin, H., Bansil, A., Hor, Y., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
The Cu-doped topological insulator Bi$_2$Se$_3$ has recently been found to undergo a superconducting transition upon cooling, raising the possibilities that it is the first known "topological superconductor" or realizes a novel non-Abelian superconducting state. Its true nature depends critically on the bulk and surface state band topology. We present the first photoemission spectroscopy results where by examining the band topology at many different copper doping values we discover that the topologically protected spin-helical surface states remain well protected and separate from bulk Dirac bands at the Fermi level where Copper pairing occurs in the optimally doped topological insulator. The addition of copper is found to result in nonlinear electron doping and strong renormalization of the topological surface states. These highly unusual observations strongly suggest that superconductivity on the topological surface of Cu$_x$Bi$_2$Se$_3$ cannot be of any conventional type in account of the general topological theory. Characteristics of the three dimensional bulk Dirac band structure are reported for the first time with respect to the superconducting doping state and topological invariant properties which should help formulate a specific theory for this novel superconductor., Comment: 4 Figures, 5 pages, Submitted December 2009
- Published
- 2009
33. A topological Dirac insulator in a quantum spin Hall phase (experimental realization of a 3D Topological Insulator)
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Hsieh, D., Qian, D., Wray, L., Xia, Y., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Disordered Systems and Neural Networks - Abstract
When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi{1-x}Sbx single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic spin-textured surface states that are higher dimensional analogues of the edge states that characterize a quantum spin Hall insulator. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy, we report the direct observation of massive Dirac particles in the bulk of Bi0.9Sb0.1, locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate "light-like" bulk carriers and topologically protected spin-textured edge-surface currents. This work is a detailed version of [Hsieh et.al., NATURE 452, 970 (2008), {Submitted in November 2007}]., Comment: 12 pages, 7 figures, This is a detailed version of the work presented at NATURE 452, 970 (2008), {Submitted in November 2007}
- Published
- 2009
34. Observation of topologically protected Dirac spin-textures and \pi Berry's phase in pure Antimony (Sb) and topological insulator BiSb
- Author
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Hsieh, D., Xia, Y., Wray, L., Qian, D., Pal, A., Dil, J. H., Meier, F., Osterwalder, J., Bihlmayer, G., Kane, C. L., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Quantum Gases - Abstract
A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry based classification of condensed matter. Exotic spin transport phenomena such as the dissipationless quantum spin Hall effect have been speculated to originate from a novel topological order whose identification requires a spin sensitive measurement. Using Spin-resolved-ARPES, we probe the spin degrees of freedom and demonstrate that topological quantum numbers are uniquely determined from spin-texture Berry Phase imaging measurements. Applying this method to pure antimony (Sb) and Bi-Sb, we identify the origin of its novel Topological Order and the negative value of the mirror Chern number. These results taken together constitute the first observation of surface electrons collectively carrying a topological Berry's phase and definite mirror Chern chirality in pure Antimony (Sb) which are the key electronic properties for realizing topological quantum computing via the interface Majorana fermion framework. This paper contains the details of the above mentioned previously reported (Science \textbf{323}, 919 (2009)) results., Comment: 6 Figures, 10 Pages, RevTex Format, Detailed version of Hsieh et.al., SCIENCE 323, 919 (2009)
- Published
- 2009
35. Time-reversal-protected single-Dirac-cone topological-insulator states in Bi2Te3 and Sb2Te3: Topologically Spin-polarized Dirac fermions with pi Berry's Phase
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Hsieh, D., Xia, Y., Qian, D., Wray, L., Dil, J. H., Meier, F., Osterwalder, J., Patthey, L., Fedorov, A. V., Lin, H., Bansil, A., Grauer, D., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Quantum Gases - Abstract
We show that the strongly spin-orbit coupled materials Bi2Te3 and Sb2Te3 (first non-Bi topological insulator) and their derivatives belong to the Z2 (Time-Reversal-Protected, elastic backscattering suppressed) topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi2Te3 is a large spin-orbit-induced indirect bulk band gap (about 150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb2Te3 exhibits similar Z2 topological properties. We demonstrate that the dynamics of surface spin-only Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for exploring novel topological physics. We emphasize (theoretically and experimentally) that the Dirac node is well within the bulk-gap and not degenerate with the bulk valence band., Comment: 5 Pages, 4 Figures, Accepted for publication in Physical Review Letters (submitted, June 2009)
- Published
- 2009
36. Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
- Author
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Xia, Y., Qian, D., Hsieh, D., Wray, L., Pal, A., Lin, H., Bansil, A., Grauer, D., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
Recent theories and experiments have suggested that strong spin-orbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topological insulator, which can show macroscopic entanglement effects. Such systems feature two-dimensional surface states whose electrodynamic properties are described not by the conventional Maxwell equations but rather by an attached axion field, originally proposed to describe strongly interacting particles. It has been proposed that a topological insulator with a single spin-textured Dirac cone interfaced with a superconductor can form the most elementary unit for performing fault-tolerant quantum computation. Here we present an angle-resolved photoemission spectroscopy study and first-principle theoretical calculation-predictions that reveal the first observation of such a topological state of matter featuring a single-surface-Dirac-cone realized in the naturally occurring Bi$_2$Se$_3$ class of materials. Our results, supported by our theoretical predictions and calculations, demonstrate that undoped compound of this class of materials can serve as the parent matrix compound for the long-sought topological device where in-plane surface carrier transport would have a purely quantum topological origin. Our study further suggests that the undoped compound reached via n-to-p doping should show topological transport phenomena even at room temperature., Comment: 3 Figures, 18 pages, Submitted to NATURE PHYSICS in December 2008
- Published
- 2009
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37. Topological Control: Systematic control of topological insulator Dirac fermion density on the surface of Bi2Te3
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Xia, Y., Qian, D., Hsieh, D., Shankar, R., Lin, H., Bansil, A., Fedorov, A. V., Grauer, D., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
Three dimensional (3D) topological insulators are quantum materials with a spin-orbit induced bulk insulating gap that exhibit quantum-Hall-like phenomena in the absence of applied magnetic fields. The proposed applications of topological insulators in device geometries rely on the ability to tune the chemical potential on their surfaces in the vicinity of the Dirac node. Here, we demonstrate a suite of surface control methods based on a combination of photo-doping and molecular-doping to systematically tune the Dirac fermion density on the topological (111) surface of Bi2Te3. Their efficacy is demonstrated via direct electronic structure topology measurements using high resolution angle-resolved photoemission spectroscopy (ARPES). These results open up new opportunities for probing topological behavior of Dirac electrons on the Bi2Te3 surface. At least one of the methods demonstrated here can be successfully applied to other topological insulators such as the Bi{1-x}Sb{x}, Sb2Te3 and Bi2Se3 which will be shown elsewhere. More importantly, our methods of topological surface state manipulation demonstrated here are highly suitable for future spectroscopic studies of topological phenomena which will complement the transport results gained from the traditional electrical gating techniques., Comment: 4 Figures, 12 pages
- Published
- 2009
38. Fermi surface topology and low-lying quasiparticle dynamics of parent Fe$_{1+x}$Te/Se Superconductor by orbital-polarization resolved ARPES
- Author
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Xia, Y., Qian, D., Wray, L., Hsieh, D., Chen, G. F., Luo, J. L., Wang, N. L., and Hasan, M. Z.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We report the first photoemission study of Fe$_{1+x}$Te - the host compound of the newly discovered iron-chalcogenide superconductors (maximum T$_c$ $\sim$ 27K). Our results reveal a pair of nearly electron-hole compensated Fermi pockets, strong Fermi velocity renormalization and an absence of a spin-density-wave gap. A shadow hole pocket is observed at the X-point of the Brillouin zone which is consistent with a long-range ordered magneto-structural groundstate. No signature of Fermi surface nesting instability associated with Q=($\pi$/2, $\pi$/2) is observed. Our results collectively reveal that the Fe$_{1+x}$Te series is dramatically different from the high T$_{c}$ pnictides and likely harbor unusual mechanism for superconductivity and magnetic order., Comment: 10 pages, 4 Figures, Accepted for publications in Physical Review Letters (2009)
- Published
- 2009
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39. First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy
- Author
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Hsieh, D., Xia, Y., Qian, D., Wray, L., Dil, J. H., Meier, F., Patthey, L., Osterwalder, J., Fedorov, A. V., Lin, H., Bansil, A., Grauer, D., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Other Condensed Matter - Abstract
Electron systems that possess light-like dispersion relations or the conical Dirac spectrum, such as graphene and bismuth, have recently been shown to harbor unusual collective states in high magnetic fields. Such states are possible because their light-like electrons come in spin pairs that are chiral,which means that their direction of propagation is tied to a quantity called pseudospin that describes their location in the crystal lattice. An emerging direction in quantum materials research is the manipulation of atomic spin-orbit coupling to simulate the effect of a spin dependent magnetic field,in attempt to realize novel spin phases of matter. This effect has been proposed to realize systems consisting of unpaired Dirac cones that are helical, meaning their direction of propagation is tied to the electron spin itself, which are forbidden to exist in graphene or bismuth. The experimental existence of topological order can not be determined without spin-resolved measurements. Here we report a spin-and angle-resolved photoemission study of the hexagonal surface of the Bi2Te3 and Bi{2-x}MnxTe3 series, which is found to exhibit a single helical Dirac cone that is fully spin-polarized. Our observations of a gap in the bulk spin-degenerate band and a spin-resolved surface Dirac node close to the chemical potential show that the low energy dynamics of Bi2Te3 is dominated by the unpaired spin-helical Dirac modes. Our spin-texture measurements prove the existence of a rare topological phase in this materials class for the first time, and suggest its suitability for novel 2D Dirac spin device applications beyond the chiral variety or traditional graphene., Comment: 13 pages, 4 figures
- Published
- 2009
40. First direct observation of Spin-textures in Topological Insulators : Spin-resolved ARPES as a probe of topological quantum spin Hall effect and Berry's phase
- Author
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Hsieh, D., Xia, Y., Wray, L., Qian, D., Pal, A., Dil, J. H., Meier, F., Osterwalder, J., Bihlmayer, G., Kane, C. L., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter - Superconductivity - Abstract
A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry based classification of condensed matter. Exotic spin transport phenomena such as the dissipationless quantum spin Hall effect have been speculated to originate from a novel topological order whose identification requires a spin sensitive measurement, which does not exist to this date in any system (neither in Hg(Cd)Te quantum wells nor in the topological insulator BiSb). Using Mott polarimetry, we probe the spin degrees of freedom of these quantum spin Hall states and demonstrate that topological quantum numbers are uniquely determined from spin texture imaging measurements. Applying this method to the Bi{1-x}Sb{x} series, we identify the origin of its novel order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a geometrical quantum (Berry's) phase and definite chirality (mirror Chern number, n_M =-1), which are the key electronic properties for realizing topological computing bits with intrinsic spin Hall-like topological phenomena. Our spin-resolved results not only provides the first clear proof of a topological insulating state in nature but also demonstrate the utility of spin-resolved ARPES technique in measuring the quantum spin Hall phases of matter., Comment: 15 pages, 3 figures, first Submitted to SCIENCE on July-22, 2008
- Published
- 2009
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41. A topological Dirac insulator in a quantum spin Hall phase : Experimental observation of first strong topological insulator
- Author
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Hsieh, D., Qian, D., Wray, L., Xia, Y., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter - Superconductivity - Abstract
When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic field. Bulk Bi$_{1-x}$Sb$_x$ single crystals are expected to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher dimensional analogues of the edge states that characterize a spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi$_{1-x}$Sb$_x$ is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest. Here, using incident-photon-energy-modulated (IPEM-ARPES), we report the first direct observation of massive Dirac particles in the bulk of Bi$_{0.9}$Sb$_{0.1}$, locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices., Comment: 16 pages, 3 Figures. Submitted to NATURE on 25th November(2007)
- Published
- 2009
- Full Text
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42. Insight into designing high-energy, high-power cathode material for lithium ion batteries
- Author
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Qian, D, Hagh, NM, and Meng, YS
- Subjects
Energy ,Chemical Engineering ,Materials Engineering ,Physical Chemistry ,Physical Chemistry (incl. Structural) - Abstract
This work reports a physical mixture aswell as an integrated composite structure (ICS) of lithium-excess layered oxides and high voltage spinel oxides. With respect to physical mixture (PM), the improvement has shown in cycling retention. Different synthesis routes would result in drastically different properties in the composite case. The optimized composite, in comparison with the non-optimized one, both energy density and the power density have increased. The optimized composite could deliver 125 mAh/g capacity after 200 cycles at a rate of 1.2 C. Thework here provides some new insights into how to design better cathode materials for lithium ion batteries. © The Author(s) 2014. Published by ECS.
- Published
- 2014
43. Experimental determination of the microscopic origin of magnetism in parent iron pnictides
- Author
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Hsieh, D., Xia, Y., Wray, L., Qian, D., Gomes, K., Yazdani, A., Chen, G. F., Luo, J. L., Wang, N. L., and Hasan, M. Z.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
Like high Tc cuprates, the newly discovered iron based superconductors lie in close proximity to a magnetically ordered parent phase. However, while the magnetic order in parent cuprates is known to derive from a spin-spin local superexchange interaction, a plethora of experiments including neutron scattering have so far been unable to conclusively resolve whether a local moment Heisenberg description applies in parent iron based compounds, or whether magnetism arises from a collective SDW order instability. These two alternatives can in principle be distinguished by measuring the low energy momentum-resolved bulk-representative electronic structure of the magnetically ordered phase. Using a combination of polarization dependent ARPES and STM, we have isolated the complete low-lying bulk representative electronic structure of magnetic SrFe2As2 with d-orbital symmetry specificity for the first time. Our results show that while multiple bands with different iron d-orbital character indeed contribute to charge transport, only one pair of bands with opposite mirror symmetries microscopically exhibit an itinerant SDW instability with energy scales on the order of 50 meV. The orbital resolved band topology below T_SDW point uniquely to a nesting driven band hybridization mechanism of the observed antiferromagnetism in the iron pnictides, and is consistent with an unusual anisotropic nodal-density-wave state. In addition, these results place strong constraints on many theories of pnictide superconductivity that require a strict local moment magnetism starting point., Comment: 16 Pages, 5 Figures; Submitted to NATURE (2009)
- Published
- 2008
44. Electrons on the surface of Bi2Se3 form a topologically-ordered two dimensional gas with a non-trivial Berry's phase
- Author
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Xia, Y., Wray, L., Qian, D., Hsieh, D., Pal, A., Lin, H., Bansil, A., Grauer, D., Hor, Y. S., Cava, R. J., and Hasan, M. Z.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter - Superconductivity - Abstract
The interface between a superconductor and a topological insulator has been proposed to harbor novel quasiparticles that realize physical schemes for fault-tolerant quantum computation. Here, we present high resolution angle-resolved photoemission experimental results, which along with first principles calculations, suggest that the surface-edge states of Bi2Se3 form a topological 2D metal. When magnetic atoms are deposited, the surface tends to lose Kramers' degeneracy and a k-space connection thread between the bulk valence and conduction bands is lost. Our observed states carry a \pi Berry's phase suggesting that although the real materials are often electron doped fully undoped Bi2Se3 would be a Z2 topological insulator at room temperature., Comment: 11 pages and 5 figures
- Published
- 2008
45. Momentum-dependence of Superconducting Gap, strong-coupling dispersion Kink, and tightly bound Cooper pairs in the high-Tc (Sr,Ba)1-x(K,Na)xFe2As2 superconductors
- Author
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Wray, L., Qian, D., Hsieh, D., Xia, Y., Li, L., Checkelsky, J. G., Pasupathy, A., Gomes, K. K., Parker, C. V., Fedorov, A. V., Chen, G. F., Luo, J. L., Yazdani, A., Ong, N. P., Wang, N. L., and Hasan, M. Z.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present a systematic angle-resolved photoemission spectroscopic study of the high-Tc superconductor class (Sr/Ba){1-x}(K/Na)xFe2As2. By utilizing a photon-energy-modulation contrast and scattering geometry we report the Fermi surface and the momentum dependence of the superconducting gap, Delta(k). A prominent quasiparticle dispersion kink reflecting strong scattering processes is observed in a binding-energy range of 25-55 meV in the superconducting state, and the coherence length or the extent of the Cooper pair wave function is found to be about 20-angstrom, which is uncharacteristic of a superconducting phase realized by the BCS-phonon-retardation mechanism. The observed 40 meV kink likely reflects contributions from the frustrated spin excitations and scattering from the soft phonons. Results taken collectively provide direct clues to the nature of the pairing potential including an internal phase-shift factor in the superconducting order parameter which leads to a Brillouin zone node in a strong-coupling setting., Comment: 12 pages + 5 figures; SC order-parameter is fit to the cosKx.cosKy function (Fig-5)
- Published
- 2008
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46. Clinical results of intensity-modulated radiotherapy for 250 patients with cervical and upper thoracic esophageal carcinoma
- Author
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Zhang J, Zhang W, Zhang B, Qian D, Li X, Zhang H, Wang Q, Zhao L, Pang Q, and Wang P
- Subjects
Cervical esophageal carcinoma;Upper esophageal carcinoma;Intensity-modulated radiotherapy;Prognosis ,Neoplasms. Tumors. Oncology. Including cancer and carcinogens ,RC254-282 - Abstract
Jiaqi Zhang, Wencheng Zhang, Baozhong Zhang, Dong Qian, Xiaoxia Li, Hualei Zhang, Qi Wang, Lujun Zhao, Qingsong Pang, Ping Wang Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Key Laboratory of Cancer Prevention and Therapy, Tianjin’s Clinical Research Center for Cancer, Tianjin 300060, People’s Republic of ChinaCorrespondence: Ping WangTianjin Medical University Cancer Institute and Hospital, Huanhu West Street, Tianjin 300060, People’s Republic of ChinaTel +86 222 334 1405Fax +86 222 334 1405Email wangping@tjmuch.comPurpose: To evaluate and analyze the efficacy and prognostic factors of intensity-modulated radiotherapy in 250 patients with cervical and upper esophageal carcinoma.Patients and methods: From September 2009 to September 2016, we retrospectively analyzed 250 patients with cervical and upper esophageal carcinoma treated with intensity-modulated radiotherapy (IMRT). In our study, all patients received IMRT, 54 patients with cervical esophageal carcinoma and 196 patients with upper esophageal carcinoma. Treatment response, survival status and failure modes of treatment were observed, and prognostic factors were analyzed.Results: The median survival time was 22.60 months and 3-year survival rate was 42%. The median progress-free survival time was 14.52 months and 3-year progress-free survival rate was 29.3%. The median survival time and the median progress-free survival time for cervical esophageal carcinoma were 20.40 and 15.15 months, respectively. The median survival time and the median progress-free survival time for upper esophageal carcinoma were 25.80 and 14.52 months, respectively (P>0.05). The significant clinical factors associated with survival were patient age, radiotherapy dose and T stages (P
- Published
- 2019
47. Tightly-bound Cooper pair, quasiparticle kinks and clues on the pairing potential in a high Tc FeAs Superconductor
- Author
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Wray, L., Qian, D., Hsieh, D., Xia, Y., Li, L., Checkelsky, J. G., Pasupathy, A., Gomes, K. K., Fedorov, A. V., Chen, G. F., Luo, J. L., Yazdani, A., Ong, N. P., Wang, N. L., and Hasan, M. Z.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We present a systematic photoemission study of the newly discovered high Tc superconductor class (Sr/Ba)1-xKxFe2As2. By utilizing a unique photon energy range and scattering geometry we resolve the details of the single particle dynamics of interacting electrons on the central Fermi surfaces of this series which shows overall strong coupling behavior (2D/kBTc = 6). Quasiparticle dispersion kinks are observed in a binding energy range of 15 to 50 meV which matches the magnetic excitation energy scales (parameterized by J1,J2). The size of the Cooper pair wavefunction is found to be less than 20A indicating a short in-plane scale uncharacteristic of a BCS-phonon scenario but suggestive of a phase factor in the global order parameter. The kink likely reflects contributions from the strongly frustrated fluctuating spin excitations and the soft phonons around 20-40 meV. Our results provide important clue to the nature of the pairing potential realized in these superconductors., Comment: 4 Figures, 5 Pages
- Published
- 2008
- Full Text
- View/download PDF
48. Reciprocal salt flux growth of LiFePO4 single crystals with controlled defect concentrations
- Author
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Janssen, Y, Santhanagopalan, D, Qian, D, Chi, M, Wang, X, Hoffmann, C, Meng, YS, and Khalifah, PG
- Subjects
olivine ,sarcopside ,endotaxy ,defects ,single crystal ,reciprocal salt ,LiFePO4 ,Fe-3(PO4)(2) ,Li3PO4 ,Fe2ClPO4 ,Chemical Sciences ,Engineering ,Materials - Abstract
Improved methods for the flux growth of single crystals of the important battery material LiFePO4 have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li1-2xFe x)FePO4 partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO4 stoichiometry. The LiFePO4 defects are shown to be sarcopside-like (2 Li+ → Fe2+ + vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO4). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO4 and sarcopside Fe3(PO4)2 in a manner that minimizes the detrimental influence of FeLi defects on the rate of Li-ion transport within crystallites. © 2013 American Chemical Society.
- Published
- 2013
49. Anomalous metallic state of Cu$_{0.07}$TiSe$_2$: an optical spectroscopy study
- Author
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Li, G., Hu, W. Z., Dong, J., Qian, D., Hsieh, D., Hasan, M. Z., Morosan, E., Cava, R. J., and Wang, N. L.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We report an optical spectroscopy study on the newly discovered superconductor Cu$_{0.07}$TiSe$_2$. Consistent with the development from a semimetal or semiconductor with a very small indirect energy gap upon doping TiSe$_2$, it is found that the compound has a low carrier density. Most remarkably, the study reveals a substantial shift of the "screened" plasma edge in reflectance towards high energy with decreasing temperature. This phenomenon, rarely seen in metals, indicates either a sizeable increase of the conducting carrier concentration or/and a decrease of the effective mass of carriers with reducing temperature. We attribute the shift primarily to the later effect., Comment: 4 figures, 4+ pages
- Published
- 2007
- Full Text
- View/download PDF
50. Anisotropic softening of collective charge modes in the vicinity of critical doping in a doped Mott insulator
- Author
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Li, Y. W., Qian, D., Wray, L., Hsieh, D., Kaga, Y., Sasagawa, T., Takagi, H., Markiewicz, R. S., Bansil, A., Eisaki, H., Uchida, S., and Hasan, M. Z.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Superconductivity - Abstract
Momentum resolved inelastic resonant x-ray scattering is used to map the evolution of charge excitations over a large range of energies, momenta and doping levels in the electron doped Mott insulator class Nd$_{2-x}$Ce$_x$CuO$_4$. As the doping induced AFM-SC (antiferromagnetic-superconducting) transition is approached, we observe an anisotropic softening of collective charge modes over a large energy scale along the Gamma to (\pi,\pi)-direction, whereas the modes exhibit broadening ($\sim$ 1 eV) with relatively little softening along Gamma to (\pi,0) with respect to the parent Mott insulator (x=0). Our study indicates a systematic collapse of the gap consistent with the scenario that the system dopes uniformly with electrons even though the softening of the modes involves an unusually large energy scale., Comment: 5 pages + 5 Figures
- Published
- 2007
- Full Text
- View/download PDF
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