26 results on '"Ying-Shuang Fu"'
Search Results
2. Charge Transfer Gap Tuning via Structural Distortion in Monolayer 1T-NbSe2
- Author
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Hu Shi, Hui-Nan Xia, Zi-Heng Ling, Liao Xin, Ying-Shuang Fu, Qiao-Yin Tang, Zhen-Yu Liu, Shuang Qiao, Wen-Hao Mao, Wen-Hao Zhang, Jing-Tao Lü, Gui-Lin Zhu, and Bing Huang
- Subjects
Materials science ,Condensed matter physics ,Mechanical Engineering ,Bilayer ,Bioengineering ,Charge (physics) ,General Chemistry ,Condensed Matter Physics ,law.invention ,Coupling (electronics) ,law ,Condensed Matter::Superconductivity ,Distortion ,Monolayer ,Coulomb ,General Materials Science ,Density functional theory ,Scanning tunneling microscope - Abstract
The Mott state in 1T-TaS2 is predicted to host quantum spin liquids (QSLs). However, its insulating mechanism is controversial due to complications from interlayer coupling. Here, we study the charge transfer state in monolayer 1T-NbSe2, an electronic analogue to TaS2 exempt from interlayer coupling, using spectroscopic imaging scanning tunneling microscopy and first-principles calculations. Monolayer NbSe2 surprisingly displays two types of star of David (SD) motifs with different charge transfer gap sizes, which are interconvertible via temperature variation. In addition, bilayer 1T-NbSe2 shows a Mott collapse by interlayer coupling. Our calculation unveils that the two types of SDs possess distinct structural distortions, altering the effective Coulomb energies of the central Nb orbital. Our calculation suggests that the charge transfer gap, the same parameter for determining the QSL regime, is tunable with strain. This finding offers a general strategy for manipulating the charge transfer state in related systems, which may be tuned into the potential QSL regime.
- Published
- 2021
3. Observation of short-range Yu-Shiba-Rusinov states with threefold symmetry in layered superconductor 2H-NbSe2
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Emi Minamitani, Xing Yang, Lang Peng, Yuan Yuan, Wen-Hao Zhang, Yang Peng, Ying-Shuang Fu, and Jing-Jing Xian
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Physics ,Superconductivity ,Condensed matter physics ,Fermi level ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,symbols.namesake ,Impurity ,law ,Condensed Matter::Superconductivity ,Lattice (order) ,0103 physical sciences ,symbols ,General Materials Science ,Density functional theory ,Surface layer ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology ,Spectroscopy - Abstract
Yu-Shiba-Rusinov (YSR) states arise when magnetic impurities interact with superconductivity. The intricacy of coupling and the nature of the superconductivity determine the behavior of the YSR state, whose detailed correlations are not yet fully understood. Here, we study the YSR state of a single Fe adatom on the surface of 2H-NbSe2 with combined low temperature scanning tunneling microscopy/spectroscopy, density functional theory calculations and tight-binding modeling. It is found that the Fe adatom occupies the hollow site of the Se surface layer. A prominent YSR state close to the Fermi level is observed. The YSR state exhibits a threefold symmetry along the diagonal direction of the Se lattice. The spatial decay of the YSR state follows a behavior in three-dimensional superconductivity. This behavior contrasts with a previous study of imbedded Fe impurities, whose YSR state shows a six-fold symmetry and a two-dimensional long-range decay. According to our theoretical modeling, the coupling configurations affect the adatom-substrate hopping and the interlayer coupling of the substrate. Both factors are crucial for the consequent behavior of the YSR state.
- Published
- 2020
4. Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na3Bi Films
- Author
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Lang Peng, Hui-Nan Xia, Yang Li, Wenhui Duan, Nianlong Zou, Ying-Shuang Fu, Wen-Hao Zhang, Min Cai, Yong Xu, and Le Qin
- Subjects
FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,Quantum phases ,010402 general chemistry ,01 natural sciences ,law.invention ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Topological order ,General Materials Science ,Physics ,Condensed Matter - Materials Science ,Potential well ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Graphene ,General Engineering ,Materials Science (cond-mat.mtrl-sci) ,Fermi energy ,021001 nanoscience & nanotechnology ,Semimetal ,0104 chemical sciences ,Topological insulator ,Scanning tunneling microscope ,0210 nano-technology - Abstract
Three-dimensional (3D) topological Dirac semimetal, when thinned down to 2D few layers, is expected to possess gapped Dirac nodes via quantum confinement effect and concomitantly display the intriguing quantum spin Hall (QSH) insulator phase. However, the 3D-to-2D crossover and the associated topological phase transition, which is valuable for understanding the topological quantum phases, remain unexplored. Here, we synthesize high-quality Na3Bi thin films with R3*R3 reconstruction on graphene, and systematically characterize their thickness-dependent electronic and topological properties by scanning tunneling microscopy/spectroscopy in combination with first-principles calculations. We demonstrate that Dirac gaps emerge in Na3Bi films, providing spectroscopic evidences of dimensional crossover from a 3D semimetal to a 2D topological insulator. Importantly, the Dirac gaps are revealed to be of sizable magnitudes on 3 and 4 monolayers (72 and 65 meV, respectively) with topologically nontrivial edge states. Moreover, the Fermi energy of a Na3Bi film can be tuned via certain growth process, thus offering a viable way for achieving charge neutrality in transport. The feasibility of controlling Dirac gap opening and charge neutrality enables realizing intrinsic high-temperature QSH effect in Na3Bi films and achieving potential applications in topological devices., 28 pages, 4 figures
- Published
- 2019
5. Realization of AlSb in the double layer honeycomb structure: a robust new class of two-dimensional material
- Author
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Kai Fan, Qiao-Yin Tang, Qinghua Zhang, Fanqi Meng, Wen-Hao Zhang, Damien West, Le Qin, Ying-Shuang Fu, Zhi-Hao Zhang, Hui-Nan Xia, Zeyu Jiang, Shengbai Zhang, and Lin Gu
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Materials science ,Band gap ,FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,01 natural sciences ,law.invention ,symbols.namesake ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Scanning transmission electron microscopy ,General Materials Science ,Condensed Matter - Materials Science ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,General Engineering ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Honeycomb structure ,Semiconductor ,symbols ,van der Waals force ,Scanning tunneling microscope ,0210 nano-technology ,business ,Molecular beam epitaxy - Abstract
Exploring new two-dimensional (2D) van der Waals (vdW) systems is at the forefront of materials physics. Here, through molecular beam epitaxy on graphene-covered SiC(0001), we report successful growth of AlSb in the double-layer honeycomb (DLHC) structure, a 2D vdW material which has no direct analogue to its 3D bulk and is predicted kinetically stable when freestanding. The structural morphology and electronic structure of the experimental 2D AlSb are characterized with spectroscopic imaging scanning tunneling microscopy and cross-sectional imaging scanning transmission electron microscopy, which compare well to the proposed DLHC structure. The 2D AlSb exhibits a bandgap of 0.93 eV versus the predicted 1.06 eV, which is substantially smaller than the 1.6 eV of bulk. We also attempt the less-stable InSb DLHC structure; however, it grows into bulk islands instead. The successful growth of a DLHC material here opens the door for the realization of a large family of novel 2D DLHC traditional semiconductors with unique excitonic, topological, and electronic properties., 21 pages, 6 figures
- Published
- 2021
6. Possible Phason-Polaron Effect on Purely One-Dimensional Charge Order of Mo6Se6 Nanowires
- Author
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Jing-Tao Lü, Le Qin, Jing-Jing Xian, Gang Li, Xing Yang, Naoto Nagaosa, Wen-Hao Zhang, Ying-Shuang Fu, and Zhi-Mo Zhang
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Materials science ,Condensed matter physics ,Nanowire ,General Physics and Astronomy ,Charge (physics) ,Electron ,Polaron ,01 natural sciences ,010305 fluids & plasmas ,law.invention ,law ,0103 physical sciences ,Monolayer ,Phason ,Scanning tunneling microscope ,010306 general physics ,Charge density wave - Abstract
In one-dimensional (1D) metallic systems, the diverging electron susceptibility and electron-phonon coupling collaboratively drive the electrons into a charge density wave (CDW) state. However, a strictly 1D system is unstable against perturbations, whose effect on CDW order requires clarification ideally with altered coupling to surroundings. Here, we fabricate such a system with nanowires of Mo6Se6 bundles, which are either attached to edges of monolayer MoSe2 or isolated freely, by postannealing the preformed MoSe2. Using scanning tunneling microscopy, we visualize charge modulations and CDW gaps with prominent coherent peaks in the edge-attached nanowires. Astonishingly, the CDW order becomes suppressed in the isolated nanowires, showing CDW correlation gaps without coherent peaks. The contrasting behavior, as revealed with theoretical modeling, is interpreted as the effect of phason polarons on the 1D CDW state. Our work elucidates a possibly unprecedented many-body effect that may be generic to strictly 1D system but undermined in a quasi-1D system.
- Published
- 2020
7. Valley dependent superconducting proximity effect in a twisted van der Waals heterojunction
- Author
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Li Chen, Jingsi Qiao, Lang Peng, Rui Li, Xin Liu, Min Cai, Wen-Hao Zhang, Jing-Jing Xian, and Ying-Shuang Fu
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Superconductivity ,Condensed Matter::Materials Science ,symbols.namesake ,Materials science ,Condensed matter physics ,Condensed Matter::Superconductivity ,Proximity effect (superconductivity) ,symbols ,Heterojunction ,Substrate (electronics) ,van der Waals force ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - Abstract
The authors uncover a valley dependent superconducting proximity effect in a heterostructure, realized by growth of multi-domain Bi(111) films on NbSe${}_{2}$ substrate, with twisted overlapping.
- Published
- 2020
8. Unusual Electronic States and Superconducting Proximity Effect of Bi Films Modulated by a NbSe2 Substrate
- Author
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Wei Ji, Jingsi Qiao, Yuhao Pan, Jing-Jing Xian, Ying-Shuang Fu, Wen-Hao Zhang, and Lang Peng
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Superconductivity ,Materials science ,Condensed matter physics ,General Engineering ,General Physics and Astronomy ,Heterojunction ,02 engineering and technology ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Characterization (materials science) ,law ,Condensed Matter::Superconductivity ,Proximity effect (superconductivity) ,Density of states ,General Materials Science ,Scanning tunneling microscope ,0210 nano-technology ,Spectroscopy - Abstract
Heterostructures of two-dimensional layered materials can be functionalized with exotic phenomena that are unpresented with each constituting component. The interface effect plays a key role in determining the electronic properties of the heterostructure, whose characterization requires a correlation with the morphology with atomic-scale precision. Here, we report an investigation on the electronic properties of few-layer Bi(110) films mediated by a NbSe2 substrate. By utilizing scanning tunneling microscopy and spectroscopy, we show a significant variation of the density of states at different Bi film thicknesses, resulting in an unusual superconducting proximity effect that deviates from the conventional monotonous decay behavior. Moreover, the electronic states of the Bi films are also prominently modulated by the Moire pattern spatially. With first-principles calculations, we illuminate these findings as the results of covalent-like quasi-bonds formed at the Bi/NbSe2 interface, which profoundly alter ...
- Published
- 2019
9. Mott phase in a van der Waals transition-metal halide at single layer limit
- Author
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Yuan Yuan, Min Cai, Zeng-Wei Zhu, Jianzhou Zhao, Zhen-Yu Liu, Ying-Shuang Fu, Gang Xu, Hui-Nan Xia, Tao Xiang, Lingxiao Zhao, Wen-Hao Zhang, Lang Peng, and Gui-Yuan Hua
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Condensed Matter::Quantum Gases ,Condensed Matter - Materials Science ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Band gap ,Mott insulator ,Scanning tunneling spectroscopy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Crystal ,symbols.namesake ,Condensed Matter::Materials Science ,Transition metal ,Mean field theory ,Phase (matter) ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,symbols ,van der Waals force - Abstract
Two-dimensional materials offer opportunities for unravelling unprecedented ordered states at single layer limit. Among such ordered states, Mott phase is rarely explored. Here, we report the Mott phase in van der Waals chromium (II) iodide (CrI2) films. High quality CrI2 films with atomically flat surface and macro size are grown on graphitized 6H-SiC(0001) substrate by molecular beam epitaxy. By in situ low temperature scanning tunneling microscopy and spectroscopy (STM/STS), we reveal that the film has a band gap as large as ~3.2 eV, which is nearly thickness independent. Density functional plus dynamic mean field theory calculations suggest that CrI2 films may be a strong Mott insulator with a ferromagnetically ordered ground state. The Mott phase is corroborated by the spectral band splitting, that is consistent with the extended Hubbard model, and gap reduction at charge dopants. Our study provides a platform for studying correlated electron states at single layer limit., Comment: 18 pages, 4 figures
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- 2019
- Full Text
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10. Quasiparticle interference of Fermi arc states in the type-II Weyl semimetal candidate WTe2
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Zhijun Wang, Xing Yang, Youguo Shi, Jing-Jing Xian, Changjiang Yi, Ying-Shuang Fu, Lang Peng, Yuan Yuan, and Jian Li
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Physics ,Condensed matter physics ,Scattering ,Scanning tunneling spectroscopy ,Weyl semimetal ,02 engineering and technology ,Type (model theory) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semimetal ,0103 physical sciences ,Quasiparticle ,Density functional theory ,010306 general physics ,0210 nano-technology ,Surface states - Abstract
Weyl semimetals possess linear dispersions through pairs of Weyl nodes in three-dimensional momentum spaces, whose hallmark arclike surface states are connected to Weyl nodes with different chirality. $\mathrm{WT}{\mathrm{e}}_{2}$ was recently predicted to be a new type of Weyl semimetal. Here, we study the quasiparticle interference (QPI) of its Fermi arc surface states by combined spectroscopic-imaging scanning tunneling spectroscopy and density functional theory calculations. We observed the electron scattering on two types of $\mathrm{WT}{\mathrm{e}}_{2}$ surfaces unambiguously. Its scattering signal can be ascribed mainly to trivial surface states. We also address the QPI feature of nontrivial surface states from theoretical calculations. The experimental QPI patterns show some features that are likely related to the nontrivial Fermi arc states, whose existence is, however, not conclusive. Our study provides an indispensable clue for studying the Weyl semimetal phase in $\mathrm{WT}{\mathrm{e}}_{2}$.
- Published
- 2018
11. Melting, Expansion Behavior and Electric Transport of In-Filling in MgO Nanotubes
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Tian Ww, Ying-Shuang Fu, Yihua Gao, Jianbo Wang, and Min Sun
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Materials science ,Transmission electron microscopy ,Biomedical Engineering ,Melting point ,General Materials Science ,Bioengineering ,Nanotechnology ,General Chemistry ,Electric transport ,Composite material ,Condensed Matter Physics - Abstract
By using a one-step approach, In-filled MgO nanotubes with diameters of 200-300 nm and lengths of several micrometers are synthesized. A Gatan heating experiment in a transmission electron microscope (TEM) shows that In-filling begins to melt far below the melting point 156.6 degrees C of In and abnormally shrinks upon increasing temperature above 270 degrees C. Massive In-filled MgO nanotubes were pressed into a disk and its resistance starts dramatically decrease upon increasing temperature above -150 degrees C, suggesting a temperature switch with a protective point -150 degrees C. The expansion and I-V characteristics were discussed.
- Published
- 2012
12. Spatially extended underscreened Kondo state from collective molecular spin
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Yousoo Kim, Emi Minamitani, Ying-Shuang Fu, Satoshi Watanabe, and Qi-Kun Xue
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Physics ,Condensed matter physics ,Spin states ,Spin polarization ,Resonance ,Charge (physics) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Intramolecular force ,Kondo effect ,Scanning tunneling microscope ,Spin (physics) - Abstract
The magnetic state and the Kondo effect in Mn phthalocyanine (MnPc) molecules on Pb(111) were investigated using low-temperature scanning tunneling microscopy (STM), density-functional theory, and numerical renormalization group calculations. We found that a unique spin state induced by the strong $\ensuremath{\pi}\ensuremath{-}d$ interaction between the Mn $d$-orbitals and ligand \ensuremath{\pi}-orbitals causes an underscreened Kondo effect observed both at Mn and the ligand. STM observations show that a Kondo resonance extends over the pyrrole ring in the Pc ligand rather than remaining localized at Mn. In gas-phase MnPc, we reveal that the $\ensuremath{\pi}\ensuremath{-}d$ interaction result in an $S=3/2$ collective spin state extended over the Pc ligand with a complex spin polarization inside the molecule. On Pb(111), charge transfer from the substrate reduces the total spin of MnPc from 3/2 to 1 while the intramolecular $\ensuremath{\pi}\ensuremath{-}d$ interaction is maintained. Partial screening of this collective $S=1$ spin state by the conduction electron in Pb(111) makes the Kondo resonance also observed at the ligand part, which is not directly hybridized with the substrate.
- Published
- 2015
13. Imaging two-component nature of Dirac-Landau levels in the topological surface state of Bi2Se3
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Tetsuo Hanaguri, Takao Sasagawa, Ying-Shuang Fu, Hidenori Takagi, Minoru Kawamura, and Kyushiro Igarashi
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Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Topological degeneracy ,Dirac (software) ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Landau quantization ,Topological entropy in physics ,Symmetry protected topological order ,Topological insulator ,Quantum mechanics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Topological order ,Topological quantum number - Abstract
Massless Dirac electrons in condensed matter have attracted considerable attention. Unlike conventional electrons, Dirac electrons are described in the form of two-component wave functions. In the surface state of topological insulators, these two components are associated with the spin degrees of freedom, hence governing the magnetic properties. Therefore, the observation of the two-component wave function provides a useful clue for exploring the novel spin phenomena. Here we show that the two-component nature is manifested in the Landau levels (LLs) whose degeneracy is lifted by a Coulomb potential. Using spectroscopic-imaging scanning tunneling microscopy, we visualize energy and spatial structures of LLs in a topological insulator Bi2Se3. The observed potential-induced LL splitting and internal structures of Landau orbits are distinct from those in a conventional electron system and are well reproduced by a two-component model Dirac Hamiltonian. Our model further predicts non-trivial energy-dependent spin-magnetization textures in a potential variation. This provides a way to manipulate spins in the topological surface state., Comment: Revised version to appear in Nature Physics. Supplementary information is available at http://www.riken.jp/epmrt/Hanaguri/SI/Bi2Se3_2comp/SI.html
- Published
- 2014
- Full Text
- View/download PDF
14. Memory effect in a topological surface state of Bi2Te2Se
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Tetsuo Hanaguri, Hidenori Takagi, Shuhei Yamamoto, Kyushiro Igarashi, Takao Sasagawa, and Ying-Shuang Fu
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Physics ,Condensed matter physics ,Dirac (software) ,General Engineering ,General Physics and Astronomy ,Conductance ,Biasing ,Landau quantization ,Topology ,Magnetic field ,law.invention ,Hysteresis ,law ,Topological insulator ,General Materials Science ,Scanning tunneling microscope - Abstract
We demonstrate the controllable local manipulation of the Dirac surface state in a topological insulator, Bi2Te2Se, which has suppressed bulk carrier density. Using scanning tunneling microscopy/spectroscopy under magnetic fields, we observe Landau levels of the Dirac surface state in the conductance spectra. The Landau levels start to shift in their energy once the bias voltage between the tip and the sample exceeds a threshold value. The amount of shift depends on the history of bias ramping. As a result, conductance spectra show noticeable hysteresis, giving rise to a memory effect. The conductance images exhibit spatially inhomogeneous patterns which can also be controlled by the bias voltage in a reproducible way. On the basis of these observations, we argue that the memory effect is associated with the tip-induced local charging effect which is pinned by the defect-generated random potential. Our study opens up a new avenue to controlling the topological surface state.
- Published
- 2013
15. Spin-resolved splitting of Kondo resonances in the presence of RKKY-type coupling
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Roland Wiesendanger, Ying-Shuang Fu, and Qi-Kun Xue
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Materials science ,Condensed matter physics ,Kondo insulator ,General Physics and Astronomy ,Resonance ,02 engineering and technology ,Electron ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,law ,Impurity ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Kondo effect ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Anderson impurity model - Abstract
We have performed spin-resolved measurements on a Kondo impurity in the presence of RKKY-type exchange coupling. By placing manganese phthalocyanine (MnPc) molecules on Fe-supported Pb islands, a Kondo system is devised which is exchange coupled to a magnetic substrate via conduction electrons in Pb, inducing spin splitting of the Kondo resonance. The spin-polarized nature of the split Kondo resonance and a spin filter effect induced by spin-flip inelastic electron tunneling are revealed by spin-polarized scanning tunneling microscopy and spectroscopy.
- Published
- 2011
16. Probing superexchange interaction in molecular magnets by spin-flip spectroscopy and microscopy
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Xucun Ma, Shuai-Hua Ji, Qi-Kun Xue, Tong Zhang, Xiaolong Zou, Wenhui Duan, Peng Cheng, Jin-Feng Jia, Ying-Shuang Fu, and Xi Chen
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Materials science ,Condensed matter physics ,Inelastic electron tunneling spectroscopy ,Scanning tunneling spectroscopy ,General Physics and Astronomy ,Spin polarized scanning tunneling microscopy ,Electrochemical scanning tunneling microscope ,law.invention ,Condensed Matter::Materials Science ,Superexchange ,law ,Chemical physics ,Condensed Matter::Strongly Correlated Electrons ,Molecular orbital ,Scanning tunneling microscope ,Spectroscopy - Abstract
The superexchange mechanism in cobalt phthalocyanine (CoPc) thin films was studied by a low temperature scanning tunneling microscope. The CoPc molecules were found to form one-dimensional antiferromagnetic chains in the film. Collective spin excitations in individual molecular chains were measured with spin-flip associated inelastic electron tunneling spectroscopy. By spatially mapping the spin-flipping channels with submolecular precision, we are able to explicitly identify the specific molecular orbitals that mediate the superexchange interaction between molecules.
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- 2008
17. Epitaxial growth and quantum well states study of Sn thin films on Sn induced Si(111)-(23×23)R30°surface
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Quan-Tong Shen, Kevin F. Kelly, L. L. Wang, Shuai-Hua Ji, Xiao Ma, Ying-Shuang Fu, Jin-Feng Jia, and Qi-Kun Xue
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Materials science ,Condensed matter physics ,Annealing (metallurgy) ,Band gap ,Fermi level ,Scanning tunneling spectroscopy ,Substrate (electronics) ,Condensed Matter Physics ,Surface energy ,Electronic, Optical and Magnetic Materials ,law.invention ,symbols.namesake ,law ,symbols ,Thin film ,Scanning tunneling microscope - Abstract
Surface morphologies and electronic structures of Sn thin films prepared on Si(111)-$\text{Sn}(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})$ $R30\ifmmode^\circ\else\textdegree\fi{}$ substrate are investigated by low temperature scanning tunneling microscopy/scanning tunneling spectroscopy (STS). A typical Stranski--Krastanov growth is observed at various growth temperatures (95--300 K), and the Sn islands above wetting layers exhibit the preferential thicknesses of odd-numbered atomic layers. STS measurement shows the formation of well-defined quantum well states with an oscillation period of 2 ML, which modulates the surface energy and accounts for the observed preferential thicknesses. Due to the interplay between large lattice mismatch and symmetry difference, a transition from $\ensuremath{\alpha}\text{-Sn}$ to $\ensuremath{\beta}\text{-Sn}$ occurs at 4 ML, which confirms the previous report. From 4 to 11 ML, the mismatch resulted strain manifests the growth via thickness-dependent striplike modulation structures on the surfaces of all Sn islands. Upon room temperature annealing, the as-deposited Sn islands undergo a metal-insulator transition, while the band gaps of wetting layers increase and oppositely shift with respect to the Fermi level for $n$- and $p$-type substrates. The change in electronic property is attributed to the electron transfer at the Sn-Si interface, which also affects the growth and morphologies of films.
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- 2008
18. High-resolution scanning tunneling spectroscopy of magnetic impurity induced bound states in the superconducting gap of Pb thin films
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Xi Chen, Tong Zhang, Shuai-Hua Ji, Wenhui Duan, Jia Li, Jin-Feng Jia, Xucun Ma, Qi-Kun Xue, and Ying-Shuang Fu
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Superconductivity ,Materials science ,Spin states ,Condensed matter physics ,Magnetism ,Band gap ,Scanning tunneling spectroscopy ,General Physics and Astronomy ,Spin polarized scanning tunneling microscopy ,law.invention ,law ,Condensed Matter::Superconductivity ,Scanning tunneling microscope ,Magnetic impurity - Abstract
Tunneling spectra for individual atoms and dimers of Mn and Cr adsorbed on superconducting Pb thin films were measured by a low temperature scanning tunneling microscope. Multiple-resonance structures within the superconducting gap on the adsorbates were resolved and interpreted as the magnetic impurity-induced bound states associated with different scattering channels. The experiment demonstrates a spectroscopic approach to characterizing the spin states of magnetic structures and exploring the competition between superconductivity and magnetism at the nanometer scale.
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- 2007
19. Manipulating the Kondo resonance through quantum size effects
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Qi-Kun Xue, Rui Wu, Chenchen Wang, Jin-Feng Jia, Bo Sun, Ying-Shuang Fu, Xi Chen, Ping Zhang, Wenhui Duan, Shuai-Hua Ji, Xiaohui Qiu, and Xucun Ma
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Materials science ,Condensed matter physics ,Kondo insulator ,Scanning tunneling spectroscopy ,General Physics and Astronomy ,Resonance ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,law.invention ,Condensed Matter::Materials Science ,law ,Quantum dot ,Condensed Matter::Strongly Correlated Electrons ,Kondo effect ,Thin film ,Scanning tunneling microscope ,Spin (physics) - Abstract
Manipulating the Kondo effect by quantum confinement has been achieved by placing magnetic molecules on silicon-supported nanostructures. The Kondo resonance of individual manganese phthalocyanine (MnPc) molecules adsorbed on the top of Pb islands was studied by scanning tunneling spectroscopy. Oscillating Kondo temperatures as a function of film thickness were observed and attributed to the formation of the thickness-dependent quantum-well states in the host Pb islands. The present approach provides a technologically feasible way for single spin manipulation by precise thickness control of thin films.
- Published
- 2007
20. The integrated spintronic functionalities of an individual high-spin state spin-crossover molecule between graphene nanoribbon electrodes
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Hua-Hua Fu, L. Zhu, Jin-Hua Gao, Jing-Tao Lü, Feng Zou, Ying-Shuang Fu, Kailun Yao, Guoying Gao, and Menghao Wu
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Spin pumping ,Nanostructure ,Materials science ,Spintronics ,Condensed matter physics ,Spin states ,Graphene ,Mechanical Engineering ,Bioengineering ,Giant magnetoresistance ,General Chemistry ,law.invention ,Mechanics of Materials ,law ,Spin crossover ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Density functional theory ,Electrical and Electronic Engineering - Abstract
The spin-polarized transport properties of a high-spin-state spin-crossover molecular junction with zigzag-edge graphene nanoribbon electrodes have been studied using density functional theory combined with the nonequilibrium Green's-function formalism. The molecular junction presents integrated spintronic functionalities such as negative differential resistance behavior, spin filter and the spin rectifying effect, associated with the giant magnetoresistance effect by tuning the external magnetic field. Furthermore, the transport properties are almost unaffected by the electrode temperature. The microscopic mechanism of these functionalities is discussed. These results represent a step toward multifunctional molecular spintronic devices on the level of the individual spin-crossover molecule.
- Published
- 2015
21. Uniform Pb nanowires of magic thickness on Si(111) controlled by elastic interaction and quantum size effects
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Lili Wang, Jin-Feng Jia, Shuai-Hua Ji, Xucun Ma, Peng Jiang, Ying-Shuang Fu, and Qi-Kun Xue
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Materials science ,Condensed matter physics ,Nanowire ,Nanotechnology ,Condensed Matter Physics ,Width ratio ,Flux rate ,Electronic, Optical and Magnetic Materials ,Quantum size ,Deposition temperature ,law.invention ,law ,Monolayer ,Scanning tunneling microscope ,Single crystal - Abstract
An ordered array of uniform single crystal Pb nanowires with a magic thickness of 9 monolayers (ML) was obtained on Si(111) by a two-step method. The coverage of 6.4 ML is critical for the formation of uniform nanowires at the deposition temperature of 200 K and the flux rate of 1.2 ML/min, while at other coverages elongated islands or interconnected stripes with various thicknesses are formed. The width ratio of the nanowires to the Si(111) substrate terraces is found to be a characteristic value of 0.54. In situ low-temperature scanning tunneling microscopy study reveals that the magic thickness and uniform distribution of the Pb nanowires are governed by the interplay between the electronic quantum size effects along the normal direction and the lateral elastic interaction induced by strain.
- Published
- 2006
22. Dissipation in an ultrathin superconducting single-crystal Pb nanobridge
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Xincheng Xie, Jian Wang, Changzhi Gu, Shuai-Hua Ji, Aizi Jin, Li Lu, Xucun Ma, Ying-Shuang Fu, Qi-Kun Xue, Mingliang Tian, Yun Qi, and Jin-Feng Jia
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Superconductivity ,Materials science ,Ion beam ,Condensed matter physics ,Transition temperature ,Nanowire ,General Physics and Astronomy ,Slip (materials science) ,Electric current ,Thin film ,Ohmic contact - Abstract
The transport property of a superconducting Pb nanobridge, which is carved by focus ion beam technique from an atomically flat single-crystal Pb thin film grown on Si(111) substrate, is investigated. Below the superconducting transition temperature TC, the nanobridge exhibits a series of sharp voltage steps as a function of current. The multiple voltage steps are interpreted as a consequence of spatially localized phase slip centers or hot-spot formation in the bridge. Just below the critical current, the voltages versus current curve shows a power-law behavior in the low temperature region, but Ohmic near the TC. The thermally activated phase slip, quantum phase slip, and imhomogeneity in a one-dimensional superconducting system may contribute to the observed results.
- Published
- 2009
23. Surface morphologies of Pb thin films on Si(111)
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Shuai-Hua Ji, Lili Wang, Xucun Ma, Peng Jiang, Jin-Feng Jia, Ying-Shuang Fu, and Qi-Kun Xue
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Silicon ,Condensed matter physics ,Annealing (metallurgy) ,chemistry.chemical_element ,Atmospheric temperature range ,Condensed Matter Physics ,Microstructure ,Semimetal ,law.invention ,chemistry ,law ,General Materials Science ,Thin film ,Scanning tunneling microscope ,Quantum tunnelling - Abstract
Surface morphologies of Pb films prepared on Si(111)-7 x 7 substrates are investigated by low temperature scanning tunnelling microscopy. Depending on substrate temperature, coverage and post-deposition annealing temperature and duration, three kinds of morphologies, uniform films, interconnected islands and isolated islands, are formed. In all three cases, preferred heights/thicknesses are observed due to the quantum size effect (QSE) along the surface normal direction. The formation and lateral distribution of either isolated islands or interconnected islands are found to be driven by competition between the boundary formation energy and the long range dipolar repulsive interaction between boundaries. With increasing substrate temperature, the critical thickness for stable films increases, which we attribute to the competition between the long range force induced by the QSE and the elastic force associated with thermal annealing.
- Published
- 2007
24. Negative magnetoresistance in fractal Pb thin films on Si(111)
- Author
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Shuai-Hua Ji, Jin-Feng Jia, Yun Qi, Xucun Ma, Jian Wang, Qi-Kun Xue, Li Lu, and Ying-Shuang Fu
- Subjects
Superconductivity ,Condensed Matter::Materials Science ,Materials science ,Fractal ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Magnetoresistance ,Annealing (metallurgy) ,Condensed Matter::Superconductivity ,Vacancy defect ,Superconducting transition temperature ,Perpendicular magnetic field ,Thin film - Abstract
Using a low temperature method, the authors have prepared atomically flat Pb ultrathin films on Si(111)-7×7 surface. Room temperature annealing of the films results in a percolation morphology with fractal vacancy islands where the Si substrate is exposed. The fractal film with a nominal thickness of 23 ML exhibits enhanced onset superconducting transition temperature of 7.0K and negative magnetoresistance with wide magnetoresistance terrace under perpendicular magnetic field when the film is in superconducting state. They attribute the phenomena to the coexistence of two superconducting phases in this fractal film.
- Published
- 2007
25. Atomic-layer-resolved local work functions of Pb thin films and their dependence on quantum well states
- Author
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Yun Qi, Qi-Kun Xue, Shuai-Hua Ji, Xucun Ma, Shengbai Zhang, Jin-Feng Jia, Peng Jiang, and Ying-Shuang Fu
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,law ,Scanning tunneling spectroscopy ,Work function ,Thin film ,Scanning tunneling microscope ,Spectroscopy ,Quantum well ,Quantum tunnelling ,Envelope (waves) ,law.invention - Abstract
The thickness dependence of the local work function (LWF) and its relationship with the quantum well states (QWSs) are studied. The measured LWF shows an oscillatory behavior between adjacent layers with a period of 2 ML and, in addition, an envelope beating pattern with a period of 9 ML. Scanning tunneling spectroscopy investigations reveal that the oscillatory LWF correlates perfectly with the formation of the QWSs: the higher the occupied QWS is, the smaller the LWF is. Through the role of the LWF, this study establishes the importance of quantum size effects in thin films for surface reactions and catalysis.
- Published
- 2007
26. Magnetoresistance oscillations of ultrathin Pb bridges
- Author
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Qi-Kun Xue, Mingliang Tian, Shuai-Hua Ji, Xincheng Xie, Jian Wang, Aizi Jin, Xucun Ma, Li Lu, Changzhi Gu, Ying-Shuang Fu, Jin-Feng Jia, and Yun Qi
- Subjects
Superconductivity ,Materials science ,Magnetoresistance ,Condensed matter physics ,Ion beam ,Nanowire ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,Condensed Matter::Materials Science ,Materials Science(all) ,law ,Condensed Matter::Superconductivity ,General Materials Science ,Thin film ,Scanning tunneling microscope ,Electrical and Electronic Engineering ,Microfabrication ,Molecular beam epitaxy - Abstract
Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb films using low-temperature molecular beam epitaxy and focus ion beam microfabrication techniques. We observed novel magnetoresistance oscillations below the superconducting transition temperature (TC) of the bridges. The oscillations—which were not seen in the crystalline Pb films—may originate from the inhomogeneity of superconductivity induced by the applied magnetic fields on approaching the normal state, or the degradation of film quality by thermal evolution.
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