42 results on '"Yanfeng GUO"'
Search Results
2. Charge fluctuations above TCDW revealed by glasslike thermal transport in kagome metals AV3Sb5 (A=K,Rb,Cs)
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Kunya Yang, Wei Xia, Xinrun Mi, Long Zhang, Yuhan Gan, Aifeng Wang, Yisheng Chai, Xiaoyuan Zhou, Xiaolong Yang, Yanfeng Guo, and Mingquan He
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- 2023
3. Electrical and thermal transport properties of the kagome metals ATi3Bi5(A=Rb,Cs)
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Xintong Chen, Xiangqi Liu, Wei Xia, Xinrun Mi, Luyao Zhong, Kunya Yang, Long Zhang, Yuhan Gan, Yan Liu, Guiwen Wang, Aifeng Wang, Yisheng Chai, Junying Shen, Xiaolong Yang, Yanfeng Guo, and Mingquan He
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- 2023
4. Magnetization tunable Weyl states in EuB6
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Jian Yuan, Xianbiao Shi, Hao Su, Xin Zhang, Xia Wang, Na Yu, Zhiqiang Zou, Weiwei Zhao, Jianpeng Liu, and Yanfeng Guo
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- 2022
5. Persistent exchange splitting in the chiral helimagnet Cr1/3NbS2
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Na Qin, Cheng Chen, Shiqiao Du, Xian Du, Xin Zhang, Zhongxu Yin, Jingsong Zhou, Runzhe Xu, Xu Gu, Qinqin Zhang, Wenxuan Zhao, Yidian Li, Sung-Kwan Mo, Zhongkai Liu, Shilei Zhang, Yanfeng Guo, Peizhe Tang, Yulin Chen, and Lexian Yang
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- 2022
6. Colossal angular magnetoresistance in the antiferromagnetic semiconductor EuTe2
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Huali Yang, Qing Liu, Zhaoliang Liao, Liang Si, Peiheng Jiang, Xiaolei Liu, Yanfeng Guo, Junjie Yin, Meng Wang, Zhigao Sheng, Yuxin Zhao, Zhiming Wang, Zhicheng Zhong, and Run-Wei Li
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- 2021
7. Observation of electronic structure and electron-boson coupling in the low-dimensional superconductor Ta4Pd3Te16
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Yiwei Li, Kun Huang, J. Y. Zhang, Simin Nie, Yulin Chen, Meixiao Wang, L. X. Yang, Wujun Shi, H. F. Yang, Xuerong Liu, H. J. Zheng, Zhe Liu, Yanfeng Guo, and Aiji Liang
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Coupling ,Superconductivity ,Physics ,Condensed matter physics ,Electronic structure ,Electron ,Boson - Published
- 2021
8. Magneto-Seebeck effect and ambipolar Nernst effect in the CsV3Sb5 superconductor
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Xinrun Mi, Mingquan He, Yuhan Gan, Aifeng Wang, Xiaoyuan Zhou, W. Xia, Yanfeng Guo, Yisheng Chai, Kunya Yang, and Long Zhang
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Superconductivity ,symbols.namesake ,Materials science ,Condensed matter physics ,Ambipolar diffusion ,Thermoelectric effect ,symbols ,Magneto ,Nernst effect - Published
- 2021
9. Magnetic structure of the topological semimetal YbMnSb2
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Ivica Zivkovic, Bachir Ouladdiaf, Hao Su, K. Beauvois, J. Alberto Rodríguez-Velamazán, Jian-Rui Soh, Yanfeng Guo, Siobhan M. Tobin, Andrew T. Boothroyd, and Anne Stunault
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Physics ,symbols.namesake ,Magnetic structure ,Fermi level ,Dirac (software) ,symbols ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Fermi energy ,Fermion ,Symmetry breaking ,Topology ,Néel temperature - Abstract
The antiferromagnetic (AFM) semimetal YbMnSb2 has recently been identified as a candidate topological material, driven by time-reversal symmetry breaking. Depending on the ordered arrangement of Mn spins below the Néel temperature, TN = 345 K, the electronic bands near the Fermi energy can either have a Dirac node, a Weyl node, or a nodal line. We have investigated the ground state magnetic structure of YbMnSb2 using unpolarized and polarized single crystal neutron diffraction. We find that the Mn moments lie along the c axis of the P4/nmm space group and are arranged in a C-type AFM structure, which implies the existence of gapped Dirac nodes near the Fermi level. The results highlight how different magnetic structures can critically affect the topological nature of fermions in semimetals.
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- 2021
10. Layer-locked spin states revealed in the centrosymmetric nodal-line semimetal HfSiS
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Mao Ye, Ding-Sheng Wang, Yanfeng Guo, X. P. Shen, Qi Jiang, Haijie Qian, C. M. Liu, Shan Qiao, Xun Zhang, Wanling Liu, and H. M. Zha
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Physics ,Spin states ,Condensed matter physics ,Dirac (software) ,Condensed Matter::Strongly Correlated Electrons ,Density functional theory ,Lambda ,Coupling (probability) ,Semimetal ,Line (formation) ,Spin-½ - Abstract
The spin-polarized bulk states in the centrosymmetric nodal-line semimetal HfSiS were observed by spin- and angle-resolved photoelectron spectroscopy. Combining with density functional theory calculations and the tight-binding model, the layer-locked spin states' nature of the observed $\mathrm{\ensuremath{\Lambda}}$-shaped bulk bands was revealed and the tight-binding model shows the importance of the next-nearest-neighbor term of spin-orbit coupling in the spin reversal of the bands along the $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\mathit{M}}$ direction. Furthermore, the topological essence of attractive Dirac node arc states was confirmed.
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- 2021
11. Electronic structure of the layered room-temperature antiferromagnet AlMn2B2
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Dawei Shen, Xiangle Lu, Zhengtai Liu, Jiacheng Gao, Yanfeng Guo, Hao Su, Zhonghao Liu, Liqin Zhou, Hongming Weng, Yaobo Huang, Shancai Wang, Man Li, and Jian Yuan
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Physics ,Condensed matter physics ,Electronic correlation ,Fermi energy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic orbital ,Ferromagnetism ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Ternary operation - Abstract
Using angle-resolved photoemission spectroscopy and band structure calculation, we have investigated the three-dimensional nature and the orbital character of the low-energy electronic structure in the layered ternary boride ${\mathrm{AlMn}}_{2}{\mathrm{B}}_{2}$, in which ferromagnetic Mn $ab$ layers couple antiferromagnetically along the $c$ axis (N\'eel temperature ${\mathrm{T}}_{\mathrm{N}}\ensuremath{\sim}320\phantom{\rule{0.28em}{0ex}}\mathrm{K}$). The calculation indicates that electronic bands in the vicinity of the Fermi energy ${E}_{\mathrm{F}}$ are dominated by the Mn $3d$ orbitals. The ${e}_{g}$ orbitals especially contribute high density of states (DOS) with large effective electron masses near ${E}_{\mathrm{F}}$. The calculated bands are renormalized by a factor of $\ensuremath{\sim}1.5$ to match the overall experimental observations, indicating moderate electronic correlation. Considering that the neighbor compound ${\mathrm{AlFe}}_{2}{\mathrm{B}}_{2}$, with one more $3d$ electron, is ferromagnetic, the high DOS near ${E}_{\mathrm{F}}$ from the different $3d$ orbitals should be associated with the different magnetic orders along the special directions in these layered ternary borides. On the other hand, our studies of electronic structure of ${\mathrm{AlMn}}_{2}{\mathrm{B}}_{2}$ would further prompt its potential applications as a layered room-temperature antiferromagnetic material.
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- 2021
12. Evidence of a topological edge state in a superconducting nonsymmorphic nodal-line semimetal
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Kui Huang, Meixiao Wang, Xun Zhang, S.M. Liu, Tao Deng, Lexian Yang, Gang Li, Lixuan Xu, Chang-Ying Wang, Yuanjun Chen, Zhongkai Liu, W. Xia, Yulin Chen, L.Y. Wei, Y. W. Li, Aiji Liang, H. J. Zheng, Yunyouyou Xia, Hongyuan Wang, H. F. Yang, and Yanfeng Guo
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Physics ,Superconductivity ,Condensed Matter - Materials Science ,Spintronics ,Photoemission spectroscopy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,Semimetal ,law.invention ,Condensed Matter::Materials Science ,law ,Condensed Matter::Superconductivity ,Topological insulator ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology - Abstract
Topological materials host fascinating low dimensional gapless states at the boundary. As a prominent example, helical topological edge states (TESs) of two-dimensional topological insulators (2DTIs) and their stacked three-dimensional (3D) equivalent, weak topological insulators (WTIs), have sparked research enthusiasm due to their potential application in the next generation of electronics/spintronics with low dissipation. Here, we propose layered superconducting material CaSn as a WTI with nontrivial Z2 as well as nodal line semimetal protected by crystalline non-symmorphic symmetry. Our systematic angle-resolved photoemission spectroscopy (ARPES) investigation on the electronic structure exhibits excellent agreement with the calculation. Furthermore, scanning tunnelling microscopy/spectroscopy (STM/STS) at the surface step edge shows signatures of the expected TES. These integrated evidences from ARPES, STM/STS measurement and corresponding ab initio calculation strongly support the existence of TES in the non-symmorphic nodal line semimetal CaSn, which may become a versatile material platform to realize multiple exotic electronic states as well as topological superconductivity.
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- 2021
13. Multiple Weyl fermions in the noncentrosymmetric semimetal LaAlSi
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Li Pi, Yimin Wan, Xia Wang, Xianbiao Shi, Shiyan Li, Yanfeng Guo, Hao Su, Zhiqiang Zou, Na Yu, Chuanying Xi, Weiwei Zhao, Jian Yuan, and Erjian Cheng
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Physics ,Zeeman effect ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Magnetism ,Fermi level ,FOS: Physical sciences ,02 engineering and technology ,Fermion ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semimetal ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,High magnetic field ,Fermi Gamma-ray Space Telescope - Abstract
The noncentrosymmetric RAlPn (R = rare earth, Pn = Si, Ge) family, predicted to host nonmagnetic and magnetic Weyl states, provide an excellent platform for investigating the relation between magnetism and Weyl physics. By using high field magnetotransport measurements and first principles calculations, we have unveiled herein both type-I and type-II Weyl states in the nonmagnetic LaAlSi. By a careful comparison between experimental results and theoretical calculations, nontrivial Berry phases associated with the Shubnikov-de Haas oscillations are ascribed to the electron Fermi pockets related to both types of Weyl points located ~ 0.1 eV above and exactly on the Fermi level, respectively. Under high magnetic field, signatures of Zeeman splitting are also observed. These results indicate that, in addition to the importance for exploring intriguing physics of multiple Weyl fermions, LaAlSi as a comparison with magnetic Weyl semimetals in the RAlPn family would also yield valuable insights into the relation between magnetism and Weyl physics., Comment: 18 pages, 5 figures, 1 table
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- 2021
14. Measurement of electronic structure and surface reconstruction in the superionic Cu2−xTe
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Yulin Chen, Zhongkai Liu, Yanfeng Guo, Juan Jiang, Meixiao Wang, Kui Huang, Yuanjun Chen, H. J. Zheng, Aiji Liang, Ding Pei, H. F. Yang, L. X. Yang, Zhang Jing, Tao Deng, S.M. Liu, and W. Xia
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Materials science ,Fluids & Plasmas ,FOS: Physical sciences ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,Engineering ,law ,Condensed Matter::Superconductivity ,0103 physical sciences ,Thermoelectric effect ,010306 general physics ,Electronic band structure ,Spectroscopy ,Condensed Matter - Materials Science ,Condensed matter physics ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Physical Sciences ,Chemical Sciences ,Scanning tunneling microscope ,0210 nano-technology ,Single crystal ,Surface reconstruction - Abstract
Recently, layered copper chalcogenides ${\mathrm{Cu}}_{2}X$ family $(X=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ has attracted tremendous research interests due to their high thermoelectric performance, which is partly due to the superionic behavior of mobile Cu ions, making these compounds ``phonon liquids.'' Here, we systematically investigate the electronic structure and its temperature evolution of the less studied single crystal ${\mathrm{Cu}}_{2\ensuremath{-}x}\mathrm{Te}$ by the combination of angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscope/spectroscopy (STM/STS) experiments. While the band structure of the ${\mathrm{Cu}}_{2\ensuremath{-}x}\mathrm{Te}$ shows agreement with the calculations, we clearly observe a $2\ifmmode\times\else\texttimes\fi{}2$ surface reconstruction from both our low temperature ARPES and STM/STS experiments which survives up to room temperature. Interestingly, our low temperature STM experiments further reveal multiple types of reconstruction patterns, which suggests the origin of the surface reconstruction being the distributed deficiency of liquidlike Cu ions. Our findings reveal the electronic structure and impurity level of ${\mathrm{Cu}}_{2}\mathrm{Te}$, which provides knowledge about its thermoelectric properties from the electronic degree of freedom.
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- 2021
15. Pressure-induced superconductivity and structural transition in ferromagnetic CrSiTe3
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Meng Wang, Ying Liu, W. Xia, Hui Liu, Yanfeng Guo, Yu Gong, Dao-Xin Yao, Wanping Cai, Changwei Wu, and Hualei Sun
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Physics ,Superconductivity ,Diffraction ,Condensed matter physics ,Magnetoresistance ,Magnetism ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Paramagnetism ,Ferromagnetism ,Hall effect ,Condensed Matter::Superconductivity ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,van der Waals force ,010306 general physics ,0210 nano-technology - Abstract
Layered structural materials have been a fertile playground to investigate mechanisms of fundamental physics and explore potential applications. Here, we report investigations on ferromagnetic van der Waals $\mathrm{Cr}\mathrm{Si}{\mathrm{Te}}_{3}$ via high-pressure synchrotron x-ray diffraction, electrical resistance, and magnetoresistance measurements. Under compression, $\mathrm{Cr}\mathrm{Si}{\mathrm{Te}}_{3}$ undergoes an insulator-metal transition and a structural transition at $\ensuremath{\sim}7.5$ GPa. Concomitantly with the structural transition, the magnetoresistance changes sign, the negative Hall coefficient increases dramatically, and superconductivity emerges at 3 K. The superconductivity persists up to the highest measured pressure of 47.1 GPa with a maximum ${T}_{c}\ensuremath{\approx}$ 4.5 K at $\ensuremath{\sim}30$ GPa. Our results suggest that $\mathrm{Cr}\mathrm{Si}{\mathrm{Te}}_{3}$ is paramagnetic in the pressure range of superconductivity. The discoveries of superconductivity and magnetic transition in ferromagnetic $\mathrm{Cr}\mathrm{Si}{\mathrm{Te}}_{3}$ under pressure provide new perspectives to explore the interplay between superconductivity and magnetism in Cr-based two-dimensional van der Waals materials.
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- 2020
16. Coupled magnetic and structural phase transitions in the antiferromagnetic polar metal Pb2CoOsO6 under pressure
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Jianping Sun, Yoshiya Uwatoko, Jinguang Cheng, Zhenhai Yu, Yuanyuan Jiao, Hai L. Feng, Kazunari Yamaura, Yanfeng Guo, Pengfei Shan, Yue-Wen Fang, Hanming Ma, Bosen Wang, and Hanghui Chen
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Physics ,Magnetic moment ,Point reflection ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Metal ,Crystallography ,Electrical resistivity and conductivity ,visual_art ,0103 physical sciences ,visual_art.visual_art_medium ,Antiferromagnetism ,Polar ,Condensed Matter::Strongly Correlated Electrons ,Anomaly (physics) ,010306 general physics ,0210 nano-technology ,Ambient pressure - Abstract
${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$ is a newly synthesized polar metal in which inversion symmetry is broken by the magnetic frustration in an antiferromagnetic ordering of Co and Os sublattices. The coupled magnetic and structural transition occurs at 45 K at ambient pressure. Here, we perform transport measurements and first-principles calculations to study the pressure effects on the magnetic/structural coupled transition of ${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$. Experimentally, we monitor the resistivity anomaly at ${T}_{N}$ under various pressures up to 11 GPa in a cubic anvil cell apparatus. We find that ${T}_{N}$ determined from the resistivity anomaly first increases quickly with pressure in a large slope of $d{T}_{N}/dP=+6.8(8)\phantom{\rule{0.28em}{0ex}}\mathrm{K}/\mathrm{GPa}$ for $Pl4\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ and, then, increases with a much reduced slope of 1.8(4) K/GPa above 4 GPa. Our first-principles calculations suggest that the observed discontinuity of $d{T}_{N}/dP$ around 4 GPa may be attributed to the vanishing of the Os magnetic moment under pressure. Pressure substantially reduces the Os moment and completely suppresses it above a critical value, which relieves the magnetic frustration in the antiferromagnetic ordering of ${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$. The Co and Os polar distortions decrease with the increasing pressure and simultaneously vanish at the critical pressure. Therefore, above the critical pressure, a new centrosymmetric antiferromagnetic state emerges in ${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$, distinct from the one under ambient pressure, thus, showing a discontinuity in $d{T}_{N}/dP$.
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- 2020
17. Electronic structure of the Si-containing topological Dirac semimetal CaAl2Si2
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Zhi Liu, Shengtao Cui, Eli Rotenberg, Hao Su, Cheng Chen, Yulin Chen, Junyi He, Yanfeng Guo, Zhongkai Liu, Kui Huang, Gang Xu, Tao Deng, Aiji Liang, Aaron Bostwick, Chengwei Wang, Lexian Yang, Chris Jozwiak, H. F. Yang, Donghui Lu, and Makoto Hashimoto
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Physics ,Photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,Semimetal ,chemistry.chemical_compound ,chemistry ,Ab initio quantum chemistry methods ,Quantum state ,Ternary compound ,Topological insulator ,0103 physical sciences ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
There has been an upsurge in the discovery of topological quantum materials, where various topological insulators and semimetals have been theoretically predicted and experimentally observed. However, very few of them contain silicon, the most widely used element in the electronics industry. Recently, ternary compound $\mathrm{CaA}{\mathrm{l}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ has been predicted to be a topological Dirac semimetal, hosting Lorentz-symmetry-violating quasiparticles with a strongly tilted conical band dispersion. In this work, by using high-resolution angle-resolved photoemission spectroscopy, we investigated the comprehensive electronic structure of $\mathrm{CaA}{\mathrm{l}}_{2}\mathrm{S}{\mathrm{i}}_{2}$. A pair of topological Dirac crossings is observed along the ${k}_{z}$ direction, in good agreement with the ab initio calculations, confirming the topological Dirac semimetal nature of the compound. Our study expands the topological material family on Si-containing compounds, which have great application potential in realizing low-cost, nontoxic electronic devices with topological quantum states.
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- 2020
18. Resonant x-ray scattering study of diffuse magnetic scattering from the topological semimetals EuCd2As2 and EuCd2Sb2
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Hao Su, D. Prabhakaran, Yanfeng Guo, Eugen Weschke, Y. G. Shi, J.-R. Soh, Enrico Schierle, Donghang Yan, and Andrew T. Boothroyd
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Physics ,Condensed matter physics ,Scattering ,X-ray ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semimetal ,Paramagnetism ,Diffuse scattering ,Ferromagnetism ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Isostructural ,010306 general physics ,0210 nano-technology ,Order of magnitude - Abstract
We have investigated the magnetic correlations in the candidate Weyl semimetals ${\mathrm{EuCd}}_{2}P{n}_{2}$ ($Pn=\mathrm{As}$, Sb) by resonant elastic x-ray scattering at the ${\mathrm{Eu}}^{2+}$ ${M}_{5}$ edge. The temperature and field dependence of the diffuse scattering of ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$ provide direct evidence that the Eu moments exhibit slow ferromagnetic (FM) correlations well above the N\'eel temperature. By contrast, the diffuse scattering in the paramagnetic phase of isostructural ${\mathrm{EuCd}}_{2}{\mathrm{Sb}}_{2}$ is at least an order of magnitude weaker. The FM correlations present in the paramagnetic phase of ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$ could create short-lived Weyl nodes.
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- 2020
19. Non-Coulomb strong electron-hole binding in Ta2NiSe5 revealed by time- and angle-resolved photoemission spectroscopy
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Yanfeng Guo, Tianwei Tang, Wentao Zhang, Yuanyuan Yang, Hongyuan Wang, Chaozhi Huang, Shaofeng Duan, and Dong Qian
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Phase transition ,Valence (chemistry) ,Materials science ,Far-infrared laser ,Physics::Optics ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electron hole ,021001 nanoscience & nanotechnology ,01 natural sciences ,Fluence ,Excited state ,0103 physical sciences ,Coulomb ,Condensed Matter::Strongly Correlated Electrons ,Atomic physics ,010306 general physics ,0210 nano-technology - Abstract
We reveal an ultrafast purely electronic phase transition in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$, which is a plausible excitonic insulator, after excited by an ultrafast infrared laser pulse. Specifically, the order parameter of the strong electron-hole binding shrinks with enhancing the pump pulse, and above a critical pump fluence, a photoexcited semimetallic state is experimentally identified with the absence of ultrafast structural transition. In addition, the bare valence and conduction bands and also the effective masses in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ are determined. These findings and detailed analysis suggest a bare nonequilibrium semimetallic phase in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ and the strong electron-hole binding cannot be exclusively driven by Coulomb interaction.
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- 2020
20. Non-Fermi-liquid behavior and saddlelike flat band in the layered ferromagnet AlFe2B2
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Dawei Shen, Zhengtai Liu, Liqin Zhou, Hao Su, Jiacheng Gao, Shancai Wang, Yanfeng Guo, Hongming Weng, Xiangle Lu, Yaobo Huang, Zhonghao Liu, and Shuai Yang
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Physics ,Condensed matter physics ,Anomalous scattering ,Fermi energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Orientation (vector space) ,Ferromagnetism ,0103 physical sciences ,Curie temperature ,Fermi liquid theory ,010306 general physics ,0210 nano-technology ,Ternary operation ,Spin-½ - Abstract
${\mathrm{AlFe}}_{2}{\mathrm{B}}_{2}$, a layered ferromagnet with a Curie temperature near room temperature (${T}_{c}\ensuremath{\sim}270$ K), has attracted growing attention recently in condensed-matter physics and materials science. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, we provide evidence of a linear band and a saddlelike flat band in the vicinity of the Fermi energy (${E}_{F}$) in ${\mathrm{AlFe}}_{2}{\mathrm{B}}_{2}$, consisting of slabs of ${\mathrm{Fe}}_{2}{\mathrm{B}}_{2}$ atoms separated by layers of Al. The anomalous scattering rate of the linear band varies linearly with the kinetic energy up to 120 meV, showing non-Fermi-liquid behavior consistent with T-linear dependence of resistivity. The flat band with ${d}_{xy}$ orbital character and with strong ${k}_{y}$ dispersion may be associated with spin orientation along the $a$ axis in layered ${\mathrm{AlFe}}_{2}{\mathrm{B}}_{2}$. Electronic and magnetic correlation can be modulated by tuning the flat band near ${E}_{F}$ in layered ternary borides. Our findings have important implications to exploit emergent physics and quantum phases in $3d$ transition metals.
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- 2020
21. Magnetotransport and ab initio calculation studies on the layered semimetal CaAl2Si2 hosting multiple nontrivial topological states
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Weiwei Zhao, Xia Wang, Xianbiao Shi, Wei Xia, Yanfeng Guo, Gang Xu, Zhenhai Yu, Hao Su, Xuesong Hanli, Na Yu, Zhiqiang Zou, and Hongyuan Wang
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Physics ,Fermi level ,Ab initio ,Fermi surface ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Topology ,Coupling (probability) ,01 natural sciences ,Brillouin zone ,symbols.namesake ,Ab initio quantum chemistry methods ,Topological insulator ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Connection (algebraic framework) ,010306 general physics ,0210 nano-technology - Abstract
We report herein the results of magnetotransport measurements and ab initio calculations on single crystalline $\mathrm{CaA}{\mathrm{l}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ semimetal. The transport properties could be understood in connection with the two-band model, agreeing well with the theoretical calculations indicating four main sheets of Fermi surface consisting of three hole pockets centered at the $\mathrm{\ensuremath{\Gamma}}$ point and one electron pocket centered at the $M$ point in the Brillouin zone. Magnetotransport measurements showed striking Shubnikov--de Haas oscillations associated with a nontrivial Berry phase, which originate from a hole Fermi pocket indicated by the ab initio calculations. The calculations also unveiled that the hole Fermi surface encloses a nodal line setting around the $\mathrm{\ensuremath{\Gamma}}$ point close to the Fermi level without considering the spin-orbit coupling (SOC). Once the SOC is included, the fragile nodal-line will be gapped and a pair of Dirac points emerge along the high symmetric $\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}A$ direction located at the Brillouin zone coordinates (0, 0, ${k}_{z}^{D}\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}0.278\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}\frac{2\ensuremath{\pi}}{c}$), about 1.22 eV below the Fermi level. In addition, the SOC can also induce a topological insulator state along the $\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}A$ direction with a gap of about 3 meV. The results demonstrate $\mathrm{CaA}{\mathrm{l}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ as an excellent platform for the study of novel topological physics with multiple nontrivial topological states.
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- 2020
22. Signature for non-Stoner ferromagnetism in the van der Waals ferromagnet Fe3GeTe2
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Yiwei Li, Gang Li, Jiun-Haw Chu, Lei Kang, Paul Malinowski, Shilei Zhang, Aiji Liang, Yulin Chen, L. X. Yang, Yanfeng Guo, Cheng Chen, X. Xu, W. Xia, Yong Xu, Shaorong Duan, Zhongkai Liu, Yuanjun Chen, and Xiaodong Xu
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Physics ,Condensed matter physics ,Magnetic moment ,Photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Ferromagnetism ,0103 physical sciences ,Quasiparticle ,symbols ,Condensed Matter::Strongly Correlated Electrons ,van der Waals force ,Itinerant magnetism ,010306 general physics ,0210 nano-technology - Abstract
The van der Waals ferromagnet $\mathrm{F}{\mathrm{e}}_{3}\mathrm{GeT}{\mathrm{e}}_{2}$ has attracted great research attention recently due to its extraordinary properties. Here, using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the temperature evolution of the electronic structure of bulk $\mathrm{F}{\mathrm{e}}_{3}\mathrm{GeT}{\mathrm{e}}_{2}$. We observe largely dispersive energy bands with exchange splitting that are in overall agreement with our density-functional theory calculation. Interestingly, the band dispersions barely change upon heating towards the ferromagnetic transition near 225 K, except for the reduction of quasiparticle coherence, which strongly deviates from the itinerant Stoner model. We suggest that the local magnetic moments may play a crucial role in the ferromagnetic ordering and the electronic structure of $\mathrm{F}{\mathrm{e}}_{3}\mathrm{GeT}{\mathrm{e}}_{2}$, which will shed light on the generic understanding of itinerant magnetism in correlated materials.
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- 2020
23. Bulk Fermi surface of the layered superconductor TaSe3 with three-dimensional strong topological state
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Linchao Ding, Zengwei Zhu, Weiwei Zhao, Leiming Chen, Li Pi, Yanfeng Guo, Yufeng Hao, Xianbiao Shi, Xufeng Kou, Wei Xia, Yong Zhang, Zhiqiang Zou, Bin Li, Na Yu, Qin Wang, Hao Su, and Xia Wang
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Superconductivity ,Physics ,Texture (cosmology) ,Quantum oscillations ,Fermi surface ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,Brillouin zone ,Ab initio quantum chemistry methods ,0103 physical sciences ,Bound state ,010306 general physics ,0210 nano-technology ,Spin-½ - Abstract
High-magnetic-field transport measurements and ab initio calculations on the layered superconductor TaSe3 have provided evidence for the existence of a three-dimensional strong topological state. Longitudinal magnetotransport measurements up to similar to 33 T unveiled striking Shubnikov-de Haas oscillations with two fundamental frequencies at 100 and 175 T corresponding to a nontrivial hole Fermi pocket at the Gamma point and a nontrivial electron Fermi pocket at the B point, respectively, in the Brillouin zone. However, calculations revealed one more electron pocket at the B point which was not detected by the magnetotransport measurements, presumably due to the limited carrier momentum relaxation time. Angle-dependent quantum oscillations by rotating the sample with respect to the magnetic field revealed clear changes in the two fundamental frequencies, indicating anisotropic electronic Fermi pockets. The ab initio calculations gave the topological Z(2) invariant of (1; 100) and revealed a single Dirac cone on the (1 0 -1) surface at the (X) over bar point with helical spin texture at a constant energy contour, suggesting a strong topological state. The results demonstrate TaSe3 as an excellent platform to study the interplay between the topological phase and superconductivity and a promising system for the exploration of topological superconductivity.
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- 2020
24. Direct observation of sixfold exotic fermions in the pyrite-structured topological semimetal PdSb2
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Dawei Shen, Zheng-Zhi Sun, Shan Qiao, Xuerong Liu, Mao Ye, Zhehong Liu, Yanfeng Guo, Jie Liu, C. Q. Hua, Yunhao Lu, and Zi Hong Liu
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Physics ,Condensed matter physics ,Photoemission spectroscopy ,Dirac (software) ,Degenerate energy levels ,02 engineering and technology ,Fermion ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Symmetry (physics) ,Semimetal ,Brillouin zone ,0103 physical sciences ,010306 general physics ,0210 nano-technology - Abstract
Pyrite-structured PdSb2 with the nonsymmorphic crystalline symmetry, has long been predicted to host sixfold-degenerate exotic fermions beyond Dirac and Weyl. Although magnetotransport measurements on PdSb2 have suggested its topologically nontrivial character, the direct spectroscopic evidence still remains absent. By utilizing high-resolution angle-resolved photoemission spectroscopy, we present a systematic study on the low-energy bulk and surface electronic structure of pyrite-structured PdSb2. Through careful comparison with first-principles calculations, we verify the existence of sixfold fermions in this compound, which are formed by three doubly degenerate bands centered at the R point in the Brillouin zone. These bands exhibit parabolic dispersion close to sixfold fermion nodes, in sharp contrast to previously reported sixfold double spin-1 chiral fermions. Furthermore, our findings reveal no protected Fermi arcs in PdSb2, which is compatible with its achiral structure. Our findings suggest that pyrite-structured PdSb2 provides an ideal platform for the investigation of fermions and their potential applications.
- Published
- 2020
25. Three-dimensional and temperature-dependent electronic structure of the heavy-fermion compound CePt2In7 studied by angle-resolved photoemission spectroscopy
- Author
-
Qi-Yi Wu, Tomasz Durakiewicz, Jianqiao Meng, Yanfeng Guo, Peter M. Oppeneer, Yu-Xia Duan, Jun He, Yaobo Huang, Shiyong Tan, Fan-Ying Wu, Yin-Zou Zhao, Haiyun Liu, Ya-Hua Yuan, Shuang-Xing Zhu, Yi Liu, Jiao-Jiao Song, Weixing Xia, Zhe Sun, Cheng Zhang, Yang Luo, Hao Liu, Jan Rusz, and Xiao-Fang Tang
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Photoemission spectroscopy ,Fermi surface ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,Photon energy ,021001 nanoscience & nanotechnology ,01 natural sciences ,0103 physical sciences ,Quasiparticle ,010306 general physics ,0210 nano-technology ,Excitation - Abstract
The three-dimensional and temperature-dependent electronic structures of the heavy-fermion superconductor ${\mathrm{CePt}}_{2}{\mathrm{In}}_{7}$ are investigated. Angle-resolved photoemission spectroscopy using variable photon energy establishes the existence of quasi-two- and three-dimensional Fermi surface topologies. Temperature-dependent $4d\text{\ensuremath{-}}4f$ on-resonance photoemission spectroscopies data reveal that heavy quasiparticle bands begin to form at a temperature well above the characteristic (coherence) temperature ${T}^{*}$. The emergence of low-lying crystal electric field excitation may be responsible for the ``relocalization'' or the precursor to the establishment of heavy electrons coherence in heavy-fermion compounds. These findings provide critical insight into understanding the hybridization in heavy-fermion systems.
- Published
- 2020
26. Magnetic structure and excitations of the topological semimetal YbMnBi2
- Author
-
Hongyuan Wang, Andrew T. Boothroyd, Yanfeng Guo, Zili Feng, Bachir Ouladdiaf, Hao Su, Alexandre S. Ivanov, Andrea Piovano, Youguo Shi, Tim Tejsner, J.-R. Soh, and Henrik Jacobsen
- Subjects
Physics ,Magnetic structure ,Spins ,Strongly Correlated Electrons (cond-mat.str-el) ,Magnon ,FOS: Physical sciences ,02 engineering and technology ,Neutron scattering ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,Inelastic neutron scattering ,Semimetal ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Antiferromagnetism ,Charge carrier ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
We investigated the magnetic structure and dynamics of YbMnBi$_2$, with elastic and inelastic neutron scattering, to shed light on the topological nature of the charge carriers in the antiferromagnetic phase. We confirm C-type antiferromagnetic ordering of the Mn spins below $T_{\rm N} = 290$ K, and determine that the spins point along the $c$-axis to within about $3^\circ$. The observed magnon spectrum can be described very well by the same effective spin Hamiltonian as was used previously to model the magnon spectrum of CaMnBi$_2$. Our results show conclusively that the creation of Weyl nodes in YbMnBi$_2$ by the time-reversal-symmetry breaking mechanism can be excluded in the bulk.
- Published
- 2019
27. Quantum oscillations and nontrivial topological state in a compensated semimetal TaP2
- Author
-
Hongyuan Wang, Wei Xia, Na Yu, Jiuyang Zhang, Xiaofei Hou, Zhenhai Yu, Xia Wang, Yanfeng Guo, Qifeng Liang, Yishi Lin, Xiaolei Liu, Yuhua Zhen, Zhiqiang Zou, Hao Su, and Yihua Wang
- Subjects
Chiral anomaly ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Mesoscale and Nanoscale Physics ,Magnetoresistance ,FOS: Physical sciences ,Quantum oscillations ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,Brillouin zone ,Condensed Matter - Strongly Correlated Electrons ,Geometric phase ,Ab initio quantum chemistry methods ,Topological insulator ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
We report systematic magneto-transport measurements and ab initio calculations on single-crystalline TaP2, a new member of the transition-metal dipnictides. We observed unsaturated magnetoresistance (MR) reaching ~ 700% at a magnetic field (B) of 9 T at 2 K along with striking Shubnikov-de Hass (SdH) oscillations. Our analysis on the SdH oscillations reveals nonzero Berry phase, indicating nontrivial band topology. The analysis also uncovers three fundamental magnetic oscillation frequencies of 72 T, 237 T, and 356 T, consistent with the theoretical calculations which reveal one hole pocket and two electron pockets at the L point and one electron pocket at the Z point of the Brillouin zone. We also found negative longitudinal MR (n-MR) within a narrow window of the angles between B and the electric current (I). The n-MR could be fitted with the Adler-Bell-Jackiw chiral anomaly equation but the origin remains yet ambiguous. The ab inito calculations suggest TaP2 as a weak topological insulator with the Z2 indices of (0; 111), which exhibits topological surface states on the (001) surface., 22 pages, 6 figures, 1 table
- Published
- 2019
28. High- Tc iron phosphide superconductivity enhanced by reemergent antiferromagnetic spin fluctuations in [Sr4Sc2O6]Fe2(As1−xPx)2 probed by NMR
- Author
-
T. Kouchi, Akira Iyo, Kazunari Yamaura, Hidekazu Mukuda, F. Engetsu, T. Shiota, Kohji Nakamura, Mamoru Yogi, Eiji Takayama-Muromachi, Mitsuharu Yashima, R. Horikawa, Yanfeng Guo, Setsuko Tajima, Katsuhiro Suzuki, Shigeki Miyasaka, and F. Sakano
- Subjects
Superconductivity ,High-temperature superconductivity ,Materials science ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,chemistry.chemical_compound ,Iron phosphide ,Lattice constant ,chemistry ,law ,Lattice (order) ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology ,Ground state ,Pnictogen - Abstract
We report a systematic NMR study on [Sr4Sc2O6]Fe-2(As1-xPx)(2), for which the local lattice parameters of the iron-pnictogen (FePn) layer are similar to those of the series LaFe(As1-x'Px')O, which exhibits two segregated antiferromagnetic (AFM) order phases, AFM1 at x' = 0 - 0.2 and AFM2 at x' = 0.4 - 0.7. Our results reveal that the parent AFM1 phase at x = 0 disappears at x = 0.3 - 0.4, corresponding to a pnictogen height (h(pn)) from the Fe plane of 1.3-1.32 angstrom, which is similar to that of LaFe(As1-x'Px')O and various parent Fe pnictides. By contrast, the AFM2 order reported for LaFe(As0.4P0.6)O does not appear at x similar to 0.8, although the local lattice parameters of the FePn layer and the microscopic electronic states are quite similar. Despite the absence of the static AFM2 order, reemergent dynamical AFM spin fluctuations were observed at approximately x similar to 0.8, which can be attributed to the instability of the AFM2 phase. We suggest this re-enhancement of AFM spin fluctuations plays a significant role in enhancing the T-c to 17 K for x = 0.8 - 1. Finally, we discuss the universality and diversity of the complicated magnetic ground states from a microscopic point of view, including the difference in the origins of the AFM1 and AFM2 phases, and their relations with the high superconducting transitions in Fe pnictides.
- Published
- 2019
29. Evidence for a Jeff=0 ground state and defect-induced spin glass behavior in the pyrochlore osmate Y2Os2O7
- Author
-
Yanfeng Guo, Donghang Yan, Henrik Jacobsen, I. da Silva, Craig V. Topping, Andrew T. Boothroyd, Y. G. Shi, Ch. J. Sahle, A. J. Princep, Franziska K. K. Kirschner, N. R. Davies, S. J. Blundell, Peter J. Baker, D. F. McMorrow, Matthew Bristow, M. C. Rahn, and J. G. Vale
- Subjects
Physics ,Spin glass ,Pyrochlore ,02 engineering and technology ,engineering.material ,Muon spin spectroscopy ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Heat capacity ,Magnetization ,Paramagnetism ,Crystallography ,0103 physical sciences ,engineering ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Ground state - Abstract
We present AC and DC magnetometry, heat capacity, muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), and resonant inelastic x-ray scattering (RIXS) studies of the pyrochlore osmate ${\mathrm{Y}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$. Consistent with previous results, we observe a small Curie-Weiss effective moment of approximately 0.4 ${\ensuremath{\mu}}_{\mathrm{B}}$ and spin freezing at a temperature ${T}_{f}\ensuremath{\simeq}5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. On the other hand, our analysis of the RIXS spectra with single-ion energy-level calculations implies a nonmagnetic ${J}_{\mathrm{eff}}=0$ ground state on the ${\mathrm{Os}}^{4+}$ sites, with the spin-orbit interaction, Hund's coupling, and trigonal distortion of ${\mathrm{OsO}}_{6}$ octahedra, all important in modeling the observed spectra. From high-field magnetization data, we show that the paramagnetic moment is most likely due to large moments ${\ensuremath{\mu}}_{\mathrm{eff}}\ensuremath{\simeq}3\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ on only a small fraction $f\ensuremath{\simeq}0.02$ of Os sites. We suggest disorder-related effects, such as oxygen nonstoichiometry or site interchange between Os and Y ions, as the most likely explanation for the magnetic response of this material.
- Published
- 2019
30. Ideal Weyl semimetal induced by magnetic exchange
- Author
-
Timur K. Kim, J. N. Blandy, Yanfeng Guo, Yulin Chen, Matthew Bristow, Juan Jiang, Steven H. Simon, Youguo Shi, Dayu Yan, Pascal Reiss, Amalia I. Coldea, M. C. Rahn, F. de Juan, Andrew T. Boothroyd, Alix McCollam, J.-R. Soh, Maia G. Vergniory, and Niels B. M. Schröter
- Subjects
Physics ,Condensed matter physics ,Spins ,Strongly Correlated Electrons (cond-mat.str-el) ,Fermi level ,Weyl semimetal ,FOS: Physical sciences ,Correlated Electron Systems ,Fermi surface ,Correlated Electron Systems / High Field Magnet Laboratory (HFML) ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Brillouin zone ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Effective mass (solid-state physics) ,0103 physical sciences ,symbols ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,Mathematics::Representation Theory ,010306 general physics ,0210 nano-technology - Abstract
Weyl semimetals exhibit exceptional quantum electronic transport due to the presence of topologically-protected band crossings called Weyl nodes. The nodes come in pairs with opposite chirality, but their number and location in momentum space is otherwise material specific. Following the initial discoveries there is now a need for better material realizations, ideally comprising a single pair of Weyl nodes located at or very close to the Fermi level and in an energy window free from other overlapping bands. Here we propose the layered intermetallic EuCd$_2$As$_2$ to be such a system. We show that Weyl nodes in EuCd$_2$As$_2$ are magnetically-induced via exchange coupling, emerging when the Eu spins are aligned by a small external magnetic field. The identification of EuCd$_2$As$_2$ as a model magnetic Weyl semimetal, evidenced here by ab initio calculations, photoemission spectroscopy, quantum oscillations and anomalous Hall transport measurements, opens the door to fundamental tests of Weyl physics.
- Published
- 2019
31. Coupling of magnetic order and charge transport in the candidate Dirac semimetal EuCd2As2
- Author
-
J. Strempfer, Yanfeng Guo, Sonia Francoual, M. C. Rahn, Andrew T. Boothroyd, L. S. I. Veiga, Donghang Yan, J.-R. Soh, Y. G. Shi, and J. R. L. Mardegan
- Subjects
Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Magnetic structure ,Magnetoresistance ,Magnetic moment ,Dirac (software) ,FOS: Physical sciences ,Charge (physics) ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology - Abstract
We use resonant elastic x-ray scattering to determine the evolution of magnetic order in EuCd$_2$As$_2$ below $T_\textrm{N}=9.5$\,K, as a function of temperature and applied magnetic field. We find an A-type antiferromagneticstructure with in-plane magnetic moments, and observe dramatic magnetoresistive effects associated with field-induced changes in the magnetic structure and domain populations. Our \textit{ab initio} electronic structure calculations indicate that the Dirac dispersion found in the nonmagnetic Dirac semimetal Cd$_3$As$_2$ is also present in EuCd$_2$As$_2$, but is gapped for $T < T_\textrm{N}$ due to the breaking of $C_3$ symmetry by the magnetic structure., Supplemental information attached to preprint
- Published
- 2018
32. Continuous critical temperature enhancement with gradual hydrogen doping in LaFeAsO0.85Hx(x=0--0.85)
- Author
-
Eiji Takayama-Muromachi, Yoshihiro Tsujimoto, Ying Sun, Xia Wang, Alexei A. Belik, Yanfeng Guo, Kazunari Yamaura, Yoshitaka Matsushita, and Jun Li
- Subjects
Physics ,Superconductivity ,Condensed matter physics ,Doping ,Fermi level ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Lattice constant ,Molecular geometry ,Hall effect ,symbols ,Density of states ,Ideal (ring theory) - Abstract
A gradual increase of the hydrogen content in LaFeAsO${}_{0.85}$H${}_{x}$ ($x$ = 0--0.85) resulted in a continuous ${T}_{\mathrm{c}}$ enhancement behavior. ${T}_{\mathrm{c}}$ increased significantly from \ensuremath{\sim}26 K ($x$ = 0) to a value of \ensuremath{\sim}35.5 K ($x$ = 0.85). As the ${T}_{\mathrm{c}}$ was enhanced, structure analysis revealed a coupled gradual contraction of the lattice constants and a reduction of the As-Fe-As bond angle towards the ideal value of 109.5\ifmmode^\circ\else\textdegree\fi{} of the regular tetrahedron. Since the Hall coefficient measurement detected no substantial change in the carrier number, optimization of structural parameters rather than carrier doping is likely to have played the leading role in the ${T}_{\mathrm{c}}$ enhancement, which could provide an important clue to the strong correlation between superconductivity and the structural parameters of iron-based superconductors. Some key phenomenological parameters, including the lower and the upper critical magnetic fields, critical current density, the density of states at the Fermi level of hydrogen-free and substituted samples, were also compared based on the magnetic and electrical characterizations, but no substantial changes were found to be associated with the hydrogen addition.
- Published
- 2012
33. Superconductivity suppression of Ba0.5K0.5Fe2−2xM2xAs2single crystals by substitution of transition metal (M = Mn, Ru, Co, Ni, Cu, and Zn)
- Author
-
Jun Li, E. Takayama-Muromachiu, Kazunari Yamaura, Hiroshi Kontani, Xia Wang, Shan Yu, Jie Yuan, S. B. Zhang, Yanfeng Guo, Ying Sun, Wei Yi, Yuichi Shirako, Yoshihiro Tsujimoto, Masaki Akaogi, and Clastin I. Sathish
- Subjects
Superconductivity ,Crystallography ,Materials science ,Transition metal ,Condensed matter physics ,Impurity ,Electrical resistivity and conductivity ,Doping ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Abstract
We investigated the doping effects of magnetic and nonmagnetic impurities in single-crystalline $p$-type Ba${}_{0.5}$K${}_{0.5}$Fe${}_{2\ensuremath{-}2x}{M}_{2x}$As${}_{2}$ ($M$ = Mn, Ru, Co, Ni, Cu, and Zn) superconductors. The superconductivity is maintained robustly with the impurity Ru, and weakly with the impurities Mn, Co, Ni, Cu, and Zn. However, the present ${T}_{c}$ suppression rate of both magnetic and nonmagnetic impurities remains much lower than what was expected for the s${}_{\ifmmode\pm\else\textpm\fi{}}$-wave model. The temperature dependence of resistivity data shows an obvious low-$T$ upturn for the crystals doped with high levels of impurity, which is due to the occurrence of localization. Thus, the relatively weak ${T}_{c}$ suppression effect from Mn, Co, Ni, Cu, and Zn is considered to be a result of localization rather than the pair-breaking effect in the ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave model.
- Published
- 2012
34. Linear decrease of critical temperature with increasing Zn substitution in the iron-based superconductor BaFe1.89−2xZn2xCo0.11As2
- Author
-
Shan Yu, Kazunari Yamaura, Eiji Takayama-Muromachi, Yanfeng Guo, Yoshihiro Tsujimoto, Hiroshi Kontani, S. B. Zhang, and Jun Li
- Subjects
Superconductivity ,Physics ,Iron-based superconductor ,Condensed matter physics ,Impurity effect ,Condensed Matter Physics ,Zn doping ,Phenomenology (particle physics) ,Electronic, Optical and Magnetic Materials - Abstract
The nonmagnetic impurity effect is studied on the Fe-based BaFe${}_{1.89\ensuremath{-}2x}$Co${}_{0.11}$As${}_{2}$ superconductor (${T}_{c}$ $=$ 25 K) with Zn substitution for Fe up to 8 at. %, which is achieved by means of high-pressure and high-temperature heating. ${T}_{c}$ decreases almost linearly with increasing Zn content and disappears at \ensuremath{\sim}8 at. %. It is different in the shared phenomenology of the early Zn doping studies, where ${T}_{c}$ decreased little. The decreasing ${T}_{c}$ rate, however, remains much lower (3.63 K/%) than what is expected for the ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave model, implying the model is inaccurate. Another symmetry model such as the non-sign-reversal $s$-wave model may better account for the result.
- Published
- 2011
35. Publisher’s Note: Integer spin-chain antiferromagnetism of the4doxide CaRuO3with post-perovskite structure [Phys. Rev. B83, 174411 (2011)]
- Author
-
Masao Arai, Xia Wang, Tetsuhiro Katsumata, Hiroshi Kojitani, Yoshiyuki Inaguma, H. Satsukawa, Yanfeng Guo, Ko-ichi Hiraki, Jun Li, Toshihiro Takahashi, Masashi Yoshida, Masaki Akaogi, Kazunari Yamaura, and Yuichi Shirako
- Subjects
Physics ,chemistry.chemical_compound ,chemistry ,Condensed matter physics ,Post-perovskite ,Structure (category theory) ,Oxide ,Antiferromagnetism ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Integer (computer science) ,Spin chain - Published
- 2011
36. Nonmagnetic pair-breaking effect in La(Fe1−xZnx)AsO0.85studied byAs75andLa139NMR and NQR
- Author
-
Keiichi Ishida, Tetsuya Iye, Kazunari Yamaura, Youguo Shi, Yoshio Nakai, Yanfeng Guo, Susumu Kitagawa, and Eiji Takayama-Muromachi
- Subjects
Superconductivity ,Crystallography ,Materials science ,Condensed matter physics ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,Crystal structure ,Normal state ,Condensed Matter Physics ,Nuclear quadrupole resonance ,Spectral line ,Electronic, Optical and Magnetic Materials ,Electronic states - Abstract
$^{75}\mathrm{As}$ and $^{139}\mathrm{La}$ NMR and nuclear quadrupole resonance (NQR) studies on Zn-substituted LaFeAsO${}_{0.85}$ have been performed to microscopically investigate the Zn-impurity effects. Although superconductivity in LaFeAsO${}_{0.85}$ disappears by 3% Zn substitution, we found that NMR/NQR spectra and NMR physical quantities in the normal state are hardly changed, indicating that the crystal structure and electronic states are not modified by Zn substitution. Our results suggest that the suppression of superconductivity by Zn substitution is not due to the change of the normal-state properties, but due to strong nonmagnetic pair-breaking effect to superconductivity.
- Published
- 2011
37. Integer spin-chain antiferromagnetism of the 4doxide CaRuO3with post-perovskite structure
- Author
-
Masao Arai, Xia Wang, Masaki Akaogi, Tetsuhiro Katsumata, Toshihiro Takahashi, Yuichi Shirako, Masashi Yoshida, Hiroshi Kojitani, Yanfeng Guo, H. Satsukawa, Ko-ichi Hiraki, Kazunari Yamaura, Yoshiyuki Inaguma, and Jun Li
- Subjects
Physics ,Condensed matter physics ,Integer ,Superexchange ,Magnetism ,Post-perovskite ,Antiferromagnetism ,Electron ,Condensed Matter Physics ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials ,Perovskite (structure) - Abstract
A quasi-one-dimensional magnetism was discovered in the post-perovskite CaRuO${}_{3}$ (Ru${}^{4+}$: $4{d}^{4}$, Cmcm), which is isocompositional with the perovskite CaRuO${}_{3}$ (Pbnm). An antiferromagnetic (AFM) spin-chain function with \ensuremath{-}$J$/${k}_{\mathrm{B}}$ $=$ 350 K reproduces the experimental curve of the magnetic susceptibility vs temperature well, suggesting long-range AFM correlations. The anisotropic magnetism is probably owed to the ${d}_{\mathit{yz}}$-$2{p}_{\mathrm{\ensuremath{\pi}}}$-${d}_{\mathit{zx}}$ and ${d}_{\mathit{zx}}$-$2{p}_{\mathrm{\ensuremath{\pi}}}$-${d}_{\mathit{yz}}$ superexchange bonds along the $a$ axis. The Sommerfeld coefficient of the specific heat is fairly small, 0.16(2) mJ mol${}^{\ensuremath{-}1}$ ${\mathrm{K}}^{\ensuremath{-}2}$, indicating that the magnetism reflects the localized nature of the 4$d$ electrons. This is an observation of an integer ($S$ $=$ 1) spin-chain AFM in the 4$d$ electron system.
- Published
- 2011
38. Structure and magnetism of the postlayered perovskite Sr3Co2O6: A possible frustrated spin-chain material
- Author
-
Xia Wang, Kazunari Yamaura, Masahiko Tanaka, S. B. Zhang, Yanfeng Guo, Yoshitaka Matsushita, Eiji Takayama-Muromachi, Yoshihiro Tsujimoto, Yong Shi, Jun Li, Yoshio Katsuya, and Keisuke Kobayashi
- Subjects
Class (set theory) ,Materials science ,Condensed matter physics ,Magnetism ,Structure (category theory) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Spin chain ,Perovskite (structure) - Abstract
For thesereasons, investigation of this class of oxides is of interestboth for materials science as well as for geological scienceand, in fact, studies aimed at developing materials that exhibitunusualsuperconductivityviacarrierdopingoftheanisotropicelectronic states are ongoing.Herein we report the successful synthesis of a denserphase of Sr
- Published
- 2011
39. Magnetic and electrical properties and carrier doping effects on the iron-based host compound Sr2ScFeAsO3
- Author
-
Masao Arai, Xia Wang, Jun Li, Kazunari Yamaura, Shan Yu, S. B. Zhang, Yanfeng Guo, Eiji Takayama-Muromachi, and Youguo Shi
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,Magnetoresistance ,Hall effect ,Electrical resistivity and conductivity ,Doping ,Charge carrier ,Conductivity ,Condensed Matter Physics ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials - Abstract
Additional charge carriers were introduced to the iron oxyarsenide Sr${}_{2}$ScFeAsO${}_{3}$ under a high-pressure condition, followed by measurements of electrical resistivity, the Hall coefficient, and magnetic susceptibility. The host compound Sr${}_{2}$ScFeAsO${}_{3}$ shows metallic conductivity down to \ensuremath{\sim}200 K and turns to show a semiconducting-like conductivity accompanied by a positive magnetoresistance ($22%$ at 70 kOe). Although the carrier density is comparable at 300 K ($5.9\ifmmode\times\else\texttimes\fi{}{10}^{21}$ cm${}^{\ensuremath{-}3}$) with that of the other Fe-based superconductors, no superconductivity appears down to 2 K. This is primarily because the net carrier density decreases over three orders of magnitude on cooling and additionally a possible magnetic order at \ensuremath{\sim}120 K prevents carriers from pairing. The properties were altered largely by introducing the additional carriers.
- Published
- 2011
40. Large decrease in the critical temperature of superconductingLaFeAsO0.85compounds doped with 3% atomic weight of nonmagnetic Zn impurities
- Author
-
E. Takayama-Muromachi, Israel Felner, Israel Nowik, Yanfeng Guo, Yoshitaka Matsushita, Shan Yu, Masahiko Tanaka, Alexei A. Belik, Keisuke Kobayashi, V. P. S. Awana, Yong Shi, Kazunari Yamaura, and Yoshio Katsuya
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Impurity ,Hall effect ,Electrical resistivity and conductivity ,Scattering ,Doping ,Condensed Matter Physics ,Spectroscopy ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials - Abstract
We observed a large decrease in ${T}_{\text{c}}$ by no more than $3\text{ }\text{at}\text{.}\text{ }\mathrm{%}$ of Zn doped into the ${T}_{\text{c}}$-optimized superconductor ${\text{LaFeAsO}}_{0.85}$ $({T}_{\text{c}}=26\text{ }\text{K})$, confirmed by measurements of electrical resistivity, magnetic susceptibility, specific heat, M\"ossbauer spectroscopy, Hall coefficient, and an electron probe microanalysis. The rate $\ensuremath{\sim}9\text{ }\text{K}/\mathrm{%}$ is remarkably higher than others achieved by nonmagnetic impurities. The ${T}_{\text{c}}$ suppression is likely due to pair breaking caused by scattering associated with the highly localized electronic state of Zn in the ${\text{Fe}}_{2}{\text{As}}_{2}$ layer. If this is true, the present result well accords with the theoretical prediction that suggests a sign reversal $s$-wave pairing model for the Fe-pnictide superconductors.
- Published
- 2010
41. Publisher's Note: Continuous metal-insulator transition of the antiferromagnetic perovskiteNaOsO3[Phys. Rev. B80, 161104(R) (2009)]
- Author
-
Tamas Varga, Yanfeng Guo, Akira Sato, Yong Shi, Masao Arai, John F. Mitchell, Alexei A. Belik, Hai-Jun Tian, J. Q. Li, H. X. Yang, E. Takayama-Muromachi, Shan Yu, Satoshi Okamoto, and Kazunari Yamaura
- Subjects
Materials science ,Condensed matter physics ,Antiferromagnetism ,Metal–insulator transition ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Perovskite (structure) - Published
- 2009
42. Continuous metal-insulator transition of the antiferromagnetic perovskiteNaOsO3
- Author
-
Masao Arai, Tamas Varga, Eiji Takayama-Muromachi, John F. Mitchell, Yanfeng Guo, Akira Sato, H. X. Yang, Satoshi Okamoto, J. Q. Li, Hai-Jun Tian, Kazunari Yamaura, Youguo Shi, Shan Yu, and Alexei A. Belik
- Subjects
Condensed Matter - Materials Science ,Materials science ,Strongly Correlated Electrons (cond-mat.str-el) ,Specific heat ,Condensed matter physics ,Band gap ,Transition temperature ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Metal ,Condensed Matter - Strongly Correlated Electrons ,Lattice (order) ,visual_art ,visual_art.visual_art_medium ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Metal–insulator transition ,Fermi gas - Abstract
Newly synthesized perovskite NaOsO3 shows Curie-Weiss metallic nature at high temperature and suddenly goes into an antiferromagnetically insulating state at 410 K on cooling. Electronic specific heat at the low temperature limit is absent, indicating that the band gap fully opens. In situ observation in electron microscopy undetected any lattice anomalies in the vicinity of the transition temperature. It is most likely that the antiferromagnetic correlation plays an essential role of the gap opening., 13 pages, 5 figures, PHYS. REV. B 80, 161104(R),(2009)
- Published
- 2009
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