33 results on '"Jhih-Shih You"'
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2. Symmetry regimes for circular photocurrents in monolayer MoSe2
- Author
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Jorge Quereda, Talieh S. Ghiasi, Jhih-Shih You, Jeroen van den Brink, Bart J. van Wees, and Caspar H. van der Wal
- Subjects
Science - Abstract
Circular photocurrents emerge in atomically thin transition metal dichalcogenides as a result of circular photogalvanic and photon drag effects. Here, the authors identify two different circular photocurrent contributions in monolater MoSe2, dominant at different voltages and with different dependence on illumination wavelength and incidence angles.
- Published
- 2018
- Full Text
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3. Entanglement spectrum and entropy in topological non-Hermitian systems and nonunitary conformal field theory
- Author
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Po-Yao Chang, Jhih-Shih You, Xueda Wen, and Shinsei Ryu
- Subjects
Physics ,QC1-999 - Abstract
We study entanglement properties of free-fermion systems without Hermiticity by use of correlation matrix and overlap matrix in the biorthogonal basis. We find at a critical point in the non-Hermitian Su-Schrieffer-Heeger (SSH) model with parity and time-reversal symmetry (PT symmetry) the entanglement entropy exhibits a logarithmic scaling with corresponding central charge c=−2, signaling the emergence of nonunitary conformal field theory. In addition, we demonstrate that, in the PT-symmetric SSH model and the non-Hermitian Chern insulators, the entanglement spectrum characterizes the topological properties in terms of the existence of mid-gap states.
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- 2020
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4. Creating Weyl nodes and controlling their energy by magnetization rotation
- Author
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Madhav Prasad Ghimire, Jorge I. Facio, Jhih-Shih You, Linda Ye, Joseph G. Checkelsky, Shiang Fang, Efthimios Kaxiras, Manuel Richter, and Jeroen van den Brink
- Subjects
Physics ,QC1-999 - Abstract
As they do not rely on the presence of any crystal symmetry, Weyl nodes are robust topological features of an electronic structure that can occur at any momentum and energy. Acting as sinks and sources of Berry curvature, Weyl nodes have been predicted to strongly affect the transverse electronic response, like in the anomalous Hall or Nernst effects. However, to observe large anomalous effects the Weyl nodes need to be close to or at the Fermi level, which implies the band structure must be tuned by an external parameter, e.g., chemical doping. Here we show that in a ferromagnetic metal tuning of the Weyl node energy and momentum can be achieved by rotation of the magnetization. First, taking as example the elementary magnet hcp-Co, we use electronic structure calculations based on density-functional theory to show that by canting the magnetization away from the easy axis, Weyl nodes can be driven exactly to the Fermi surface. Second, we show that the same phenomenology applies to the kagome ferromagnet Co_{3}Sn_{2}S_{2}, in which we additionally show how the dynamics in energy and momentum of the Weyl nodes affects the calculated anomalous Hall and Nernst conductivities. Our results highlight how the intrinsic magnetic anisotropy can be used to engineer Weyl physics.
- Published
- 2019
- Full Text
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5. Many-body formation and dissociation of a dipolar chain crystal
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Jhih-Shih You and Daw-Wei Wang
- Subjects
dipolar chain ,crystal ,quantum phase transition ,05.30.Rt ,36.20.-r ,67.85.-d ,Science ,Physics ,QC1-999 - Abstract
We propose an experimental scheme to effectively assemble chains of dipolar gases with a uniform length in a multi-layer system. The obtained dipolar chains can form a chain crystal with the system temperature easily controlled by the initial lattice potential and the external field strength during processing. When the density of chains increases, we further observe a second order quantum phase transition for the chain crystal to be dissociated toward layers of 2D crystal, where the quantum fluctuation dominates the classical energy and the compressibility diverges at the phase boundary. The experimental implication of such a dipolar chain crystal and its quantum phase transition is also discussed.
- Published
- 2014
- Full Text
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6. Nonlinear photoconductivities and quantum geometry of chiral multifold fermions
- Author
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Hsiu-Chuan Hsu, Jhih-Shih You, Junyeong Ahn, and Guang-Yu Guo
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Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences - Abstract
Chiral multifold fermions are quasi-particles that appear only in chiral crystals such as transition metal silicides in the cubic B20 structure (i.e., the CoSi family), and they may show exotic physical properties. Here we study the injection and shift photoconductivities and also the related geometrical quantities for several types of chiral multifold fermions, including spin-1/2 as well as pseudospin-1 and -3/2 fermions, dubbed as Kramers Weyl, triple point and Rarita-Schwinger-Weyl (RSW) fermions, respectively. We utilize the minimal symmorphic model to describe the triple point fermions (TPF). We also consider the more realistic model Hamiltonian for the CoSi family including both linear and quadratic terms. We find that circular injection currents are quantized as a result of the Chern numbers carried by the multifold fermions within the linear models. Surprisingly, we discover that in the TPF model, linear shift conductivities are proportional to the pseudo spin-orbit coupling and independent of photon frequency. In contrast, for the RSW and Kramer Weyl fermions, the linear shift conductivity is linearly proportional to photon frequency. The numerical results agree with the power-counting analysis for quadratic Hamiltonians. The frequency independence of the linear shift conductivity could be attributed to the strong resonant symplectic Christoffel symbols of the flat bands. Moreover, the calculated symplectic Christoffel symbols show significant peaks at the nodes, suggesting that the shift currents are due to the strong geometrical response near the topological nodes.
- Published
- 2023
7. Magnetoconductance modulations due to interlayer tunneling in radial superlattices
- Author
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Yu-Jie Zhong, Angus Huang, Hui Liu, Xuan-Fu Huang, Horng-Tay Jeng, Jhih-Shih You, Carmine Ortix, and Ching-Hao Chang
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Condensed Matter - Materials Science ,Quantum Physics ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Materials Science ,Quantum Physics (quant-ph) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - Abstract
Radial superlattices are nanostructured materials obtained by rolling-up thin solid films into spiral-like tubular structures. The formation of these "high-order" superlattices from two-dimensional crystals or ultrathin films is expected to result in a transition of transport characteristics from two-dimensional to one-dimensional. Here, we show that a transport hallmark of radial superlattices is the appearance of magnetoconductance modulations in the presence of externally applied axial magnetic fields. This phenomenon critically relies on electronic interlayer tunneling processes that activates an unconventional Aharonov-Bohm-like effect. Using a combination of density functional theory calculations and low-energy continuum models, we determine the electronic states of a paradigmatic single-material radial superlattice -- a two-winding carbon nanoscroll -- and indeed show momentum-dependent oscillations of the magnetic states in axial configuration, which we demonstrate to be entirely due to hopping between the two windings of the spiral-shaped scroll., Comment: 21 pages, 4 figures. To appear in Nanoscale Horizons
- Published
- 2022
8. Non-Hermitian Many-Body Localization of Coupled Hatano-Nelson Chains
- Author
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Hsiang-Hua Jen, Jhih-Shih You, Yi-Ping Huang, Yi-Cheng Wang, and Kuldeep Suthar
- Published
- 2022
9. Non-Hermitian Many-Body Localization with Open Boundaries
- Author
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Kuldeep Suthar, Yi-Cheng Wang, Yi-Ping Huang, H. H. Jen, and Jhih-Shih You
- Subjects
Quantum Gases (cond-mat.quant-gas) ,FOS: Physical sciences ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter - Quantum Gases - Abstract
The explorations of non-Hermiticity have been devoted to investigate the disorder-induced many-body localization (MBL). However, the sensitivity of the spatial boundary conditions and the interplay of the non-Hermitian skin effect with many-body phenomena are not yet clear. For a MBL system in the presence of non-reciprocal tunnelings and random disorder potential, we identify two different complex-real spectral transitions, one is present for both open and periodic boundaries while the other is present only for open boundaries of a coupled non-Hermitian chains. The later is driven due to the inter-chain coupling at weak disorder where the level statistics of the real eigenenergy phase follows Gaussian orthogonal ensemble. We further characterize wavefunctions through the (biorthogonal) inverse participation ratio and fractal dimension, which reveal the suppression of skin effect in the non-Hermitian MBL phase. Finally, we demonstrate that the quench dynamics of the local particle density, spin imbalance, and entanglement entropy also signify the hallmark of the boundary effects and non-ergodic character of many-body localization., 11 pages, 10 figures; version accepted for publication in Phys. Rev. B
- Published
- 2022
10. A non-Hermitian optical atomic mirror
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Jhih-Shih You, Hsiang-Hua Jen, and Yi-Cheng Wang
- Subjects
Quantum Physics ,Multidisciplinary ,Quantum Gases (cond-mat.quant-gas) ,Atomic Physics (physics.atom-ph) ,FOS: Physical sciences ,General Physics and Astronomy ,General Chemistry ,Quantum Physics (quant-ph) ,Condensed Matter - Quantum Gases ,General Biochemistry, Genetics and Molecular Biology ,Optics (physics.optics) ,Physics - Atomic Physics ,Physics - Optics - Abstract
Explorations of symmetry and topology have led to important breakthroughs in quantum optics, but much richer behaviors arise from the non-Hermitian nature of light-matter interactions. A high-reflectivity, non-Hermitian optical mirror can be realized by a two-dimensional subwavelength array of neutral atoms near the cooperative resonance associated with the collective dipole modes. Here we show that exceptional points develop from a nondefective degeneracy by lowering the crystal symmetry of a square atomic lattice, and dispersive bulk Fermi arcs that originate from exceptional points are truncated by the light cone. We also find, although the dipole-dipole interaction is reciprocal, the geometry-dependent non-Hermitian skin effect emerges. Furthermore, skin modes localized at a boundary show a scale-free behavior that stems from the long-range interaction and whose mechanism goes beyond the framework of non-Bloch band theory. Our work opens the door to the study of the interplay among non-Hermiticity, topology, and long-range interaction., 8 + 20 pages, 4 + 7 figures
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- 2022
11. Supermetal-insulator transition in a non-Hermitian network model
- Author
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Hui Liu, Shinsei Ryu, Jhih-Shih You, and Ion Cosma Fulga
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Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Critical point (thermodynamics) ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences ,Skin effect ,Renormalization group ,Approx ,Divergence (computer science) ,Hermitian matrix ,Critical exponent ,Symmetry (physics) ,Mathematical physics - Abstract
We study a non-Hermitian and non-unitary version of the two-dimensional Chalker-Coddington network model with balanced gain and loss. This model belongs to the class D^dagger with particle-hole symmetry^dagger and hosts both the non-Hermitian skin effect as well as exceptional points. By calculating its two-terminal transmission, we find a novel contact effect induced by the skin effect, which results in a non-quantized transmission for chiral edge states. In addition, the model exhibits an insulator to 'supermetal' transition, across which the transmission changes from exponentially decaying with system size to exponentially growing with system size. In the clean system, the critical point separating insulator from supermetal is characterized by a non-Hermitian Dirac point that produces a quantized critical transmission of 4, instead of the value of 1 expected in Hermitian systems. This change in critical transmission is a consequence of the balanced gain and loss. When adding disorder to the system, we find a critical exponent for the divergence of the localization length \nu \approx 1, which is the same as that characterizing the universality class of two-dimensional Hermitian systems in class D. Our work provides a novel way of exploring the localization behavior of non-Hermitian systems, by using network models, which in the past proved versatile tools to describe Hermitian physics., Comment: 18 pages, 12 figures, and 4 tables. Comments are welcome
- Published
- 2021
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12. Infinite Berry Curvature of Weyl Fermi Arcs
- Author
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Jorge I. Facio, Inti Sodemann, Jhih-Shih You, Jeroen van den Brink, and Dennis Wawrzik
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Surface (mathematics) ,Physics ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,FOS: Physical sciences ,General Physics and Astronomy ,Weyl semimetal ,Ultracold matter ,Brillouin zone ,Dipole ,Hall effect ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Berry connection and curvature ,Dispersion (water waves) ,Surface states - Abstract
We show that Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry curvature scaling as $1/k^2$, where $k$ is the distance to a hot-line in the surface Brillouin zone that connects the projection of Weyl nodes with opposite chirality but which is distinct from the Fermi arc itself. Such surface Berry curvature appears whenever the bulk Weyl dispersion has a velocity tilt toward the surface of interest. This divergence is reflected in a variety of Berry curvature mediated effects that are readily accessible experimentally, and in particular leads to a surface Berry curvature dipole that grows linearly with the thickness of a slab of a Weyl semimetal material in the limit of long lifetime of surface states. This implies the emergence of a gigantic contribution to the non-linear Hall effect in such devices., 5+2 pages, 2+1 figures, v2; this is the final, published version
- Published
- 2020
13. Crossover from a delocalized to localized atomic excitation in an atom-waveguide interface
- Author
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Hsiang-Hua Jen and Jhih-Shih You
- Subjects
Physics ,Quantum Physics ,Level repulsion ,Photon ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,FOS: Physical sciences ,Quantum entanglement ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,010305 fluids & plasmas ,symbols.namesake ,Delocalized electron ,0103 physical sciences ,Atom ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Dissipative system ,symbols ,010306 general physics ,Hamiltonian (quantum mechanics) ,Quantum Physics (quant-ph) ,Quantum - Abstract
An atom-waveguide system, which presents one of the quantum interfaces that enable strong couplings between light and atoms, can support tightly-confined guided modes of light. In this distinctive quantum interface, we theoretically investigate the crossover from a delocalized to localized atomic excitation under long-range dipole-dipole interactions and lattice disorders. Both localization lengths of the excitation distributions and power-law scalings of dissipative von Neumann entanglement entropy show signatures of this crossover. We further calculate numerically the level statistics of the underlying non-Hermitian Hamiltonian, from which as the disorder strength increases, the gap ratio decreases and the intrasample variance increases before reaching respective saturated values. The mean gap ratio in the deeply localized regime is close to the one from Poisson statistics along with a relatively large intrasample variance, whereas in the nondisordered regime, a significant level repulsion emerges. Our results provide insights to study the non-ergodic phenomenon in an atom-waveguide interface, which can be potentially applied to photon storage in this interface under dissipations., Comment: 4 figures
- Published
- 2020
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14. Creating Weyl nodes and controlling their energy by magnetization rotation
- Author
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Jorge I. Facio, Jhih-Shih You, Linda Ye, Joseph Checkelsky, Madhav Prasad Ghimire, Manuel Richter, Jeroen van den Brink, Shiang Fang, and Efthimios Kaxiras
- Subjects
FOS: Physical sciences ,02 engineering and technology ,Anomalous Hall effect ,Rotation ,01 natural sciences ,Thermoelectric effects ,Condensed Matter - Strongly Correlated Electrons ,First-principles calculations ,Magnetization ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,010306 general physics ,Physics ,Annihilation ,Condensed Matter - Mesoscale and Nanoscale Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Topological materials ,Order (ring theory) ,Fermi surface ,021001 nanoscience & nanotechnology ,Orientation (vector space) ,Magnet ,0210 nano-technology ,Energy (signal processing) ,Weyl semimetal - Abstract
As they do not rely on the presence of any crystal symmetry, Weyl nodes are robust topological features of an electronic structure that can occur at any momentum and energy. Acting as sinks and sources of Berry curvature, Weyl nodes have been predicted to strongly affect the transverse electronic response, like in the anomalous Hall or Nernst effects. However, to observe large anomalous effects the Weyl nodes need to be close to or at the Fermi-level, which implies the band structure must be tuned by an external parameter, e.g. chemical doping or pressure. Here we show that in a ferromagnetic metal tuning of the Weyl node energy and momentum can be achieved by rotation of the magnetization. Taking Co$_3$Sn$_2$S$_2$ as an example, we use electronic structure calculations based on density-functional theory to show that not only new Weyl fermions can be created by canting the magnetization away from the easy axis, but also that the Weyl nodes can be driven exactly to the Fermi surface. We also show that the dynamics in energy and momentum of the Weyl nodes strongly affect the calculated anomalous Hall and Nernst conductivities., Comment: Supp. Material added
- Published
- 2019
15. Atomtronics with a spin: Statistics of spin transport and nonequilibrium orthogonality catastrophe in cold quantum gases
- Author
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Dmitri Ivanov, Richard Schmidt, Jhih-Shih You, Eugene Demler, and Michael Knap
- Subjects
Quantum decoherence ,Population ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,Ramsey interferometry ,Ultracold atom ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Atom ,Statistics ,010306 general physics ,education ,Condensed Matter - Statistical Mechanics ,Spin-½ ,Physics ,Quantum Physics ,education.field_of_study ,Condensed Matter - Mesoscale and Nanoscale Physics ,Statistical Mechanics (cond-mat.stat-mech) ,021001 nanoscience & nanotechnology ,3. Good health ,Quantum Gases (cond-mat.quant-gas) ,Atomtronics ,Condensed Matter::Strongly Correlated Electrons ,Condensed Matter - Quantum Gases ,Quantum Physics (quant-ph) ,0210 nano-technology ,Fermi gas - Abstract
We propose to investigate the full counting statistics of nonequilibrium spin transport with an ultracold atomic quantum gas. The setup makes use of the spin control available in atomic systems to generate spin transport induced by an impurity atom immersed in a spin-imbalanced two-component Fermi gas. In contrast to solid-state realizations, in ultracold atoms spin relaxation and the decoherence from external sources is largely suppressed. As a consequence, once the spin current is turned off by manipulating the internal spin degrees of freedom of the Fermi system, the nonequilibrium spin population remains constant. Thus one can directly count the number of spins in each reservoir to investigate the full counting statistics of spin flips, which is notoriously challenging in solid state devices. Moreover, using Ramsey interferometry, the dynamical impurity response can be measured. Since the impurity interacts with a many-body environment that is out of equilibrium, our setup provides a way to realize the non-equilibrium orthogonality catastrophe. Here, even for spin reservoirs initially prepared in a zero-temperature state, the Ramsey response exhibits an exponential decay, which is in contrast to the conventional power-law decay of Anderson's orthogonality catastrophe. By mapping our system to a multi-step Fermi sea, we are able to derive analytical expressions for the impurity response at late times. This allows us to reveal an intimate connection of the decay rate of the Ramsey contrast and the full counting statistics of spin flips., Comment: 9+11 pages, 10 figures
- Published
- 2019
16. Topological Nonlinear Anomalous Nersnt Effect in Strained Transition Metal Dichalcogenides
- Author
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Tony Low, Zhen-Gang Zhu, Jhih-Shih You, Xiao Qin Yu, and Gang Su
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Physics ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Point reflection ,Semiclassical physics ,FOS: Physical sciences ,Fermi surface ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Temperature gradient ,Nonlinear system ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,symbols ,Nernst equation ,Berry connection and curvature ,010306 general physics ,0210 nano-technology ,Nernst effect - Abstract
We theoretically analyze the non-linear anomalous Nernst effect as the second-order response of temperature gradient by using the semiclassical framework of electron dynamics. We find that a non-linear current can be generated transverse to the applied temperature gradient in time-reversal-symmetry materials with broken inversion symmetry. This effect has a quantum origin arising from the Berry curvature of states near the Fermi surface. We discuss the non-linear Nernst effect in transition metal dichalcogenides~(TMDCs) under the application of uniaxial strain. In particular, we predict that under fixed chemical potential in TMDCs, the non-linear Nernst current exhibits a transition from $\textbf{j}^\text{dip}_\text{A}\sim T^{-2}$ temperature dependence in low temperature regime to a linear $T$-dependence in high temperature., 5 pages, 2 figures
- Published
- 2019
17. Dirac fermions and flat bands in the ideal kagome metal FeSn
- Author
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David Graf, Abe Levitan, Minyong Han, Chris Jozwiak, Linda Ye, Ross D. McDonald, Riccardo Comin, Efthimios Kaxiras, Shiang Fang, Jorge I. Facio, David C. Bell, Mingu Kang, Aaron Bostwick, Jhih-Shih You, Eli Rotenberg, Mun Chan, Jeroen van den Brink, Madhav Prasad Ghimire, Joseph Checkelsky, Konstantine Kaznatcheev, Elio Vescovo, and Manuel Richter
- Subjects
Magnetism ,High Energy Physics::Lattice ,FOS: Physical sciences ,02 engineering and technology ,7. Clean energy ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Atomic orbital ,Lattice (order) ,0103 physical sciences ,Antiferromagnetism ,General Materials Science ,Nanoscience & Nanotechnology ,010306 general physics ,Electronic band structure ,Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Mechanical Engineering ,Quantum oscillations ,General Chemistry ,Fermion ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Dirac fermion ,Mechanics of Materials ,symbols ,Condensed Matter::Strongly Correlated Electrons ,cond-mat.str-el ,0210 nano-technology - Abstract
The kagome lattice based on 3d transition metals is a versatile platform for novel topological phases hosting symmetry-protected electronic excitations and exotic magnetic ground states. However, the paradigmatic states of the idealized two-dimensional (2D) kagome lattice - Dirac fermions and topological flat bands - have not been simultaneously observed, partly owing to the complex stacking structure of the kagome compounds studied to date. Here, we take the approach of examining FeSn, an antiferromagnetic single-layer kagome metal with spatially-decoupled kagome planes. Using polarization- and termination-dependent angle-resolved photoemission spectroscopy (ARPES), we detect the momentum-space signatures of coexisting flat bands and Dirac fermions in the vicinity of the Fermi energy. Intriguingly, when complemented with bulk-sensitive de Haas-van Alphen (dHvA) measurements, our data reveal an even richer electronic structure that exhibits robust surface Dirac fermions on specific crystalline terminations. Through band structure calculations and matrix element simulations, we demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals under kagome symmetry, while the surface state realizes a rare example of fully spin-polarized 2D Dirac fermions when combined with spin-layer locking in FeSn. These results highlight FeSn as a prototypical host for the emergent excitations of the kagome lattice. The prospect to harness these excitations for novel topological phases and spintronic devices is a frontier of great promise at the confluence of topology, magnetism, and strongly-correlated electron physics.
- Published
- 2019
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18. Strongly Enhanced Berry Dipole at Topological Phase Transitions in BiTeI
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Dmitri V. Efremov, Klaus Koepernik, Jorge I. Facio, Inti Sodemann, Jeroen van den Brink, and Jhih-Shih You
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Physics ,Phase transition ,Condensed Matter - Mesoscale and Nanoscale Physics ,General Physics and Astronomy ,chemistry.chemical_element ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,Bismuth ,Dipole ,Nonlinear system ,Phase transitions and critical phenomena ,Orders of magnitude (time) ,chemistry ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Polar ,Berry connection and curvature ,010306 general physics ,0210 nano-technology ,Tellurium - Abstract
Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here we focus on the giant-Rashba material bismuth tellurium iodine (BiTeI) which exhibits a pressure-driven phase transition between topological and trivial insulators in three-dimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semi-metallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berrry-dipole --a vector along the polar axis of this material-- has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points, at which the nonlinear Hall conductivity can increase by over two orders of magnitude., Comment: As accepted in PRL
- Published
- 2018
19. Collective resonances near zero energy induced by a point defect in bilayer graphene
- Author
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Jian-Ming Tang, Wen-Min Huang, and Jhih-Shih You
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Physics ,Mesoscopic physics ,Multidisciplinary ,Local density of states ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Scattering ,lcsh:R ,FOS: Physical sciences ,lcsh:Medicine ,Zero-point energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Delocalized electron ,Singularity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Thermodynamic limit ,lcsh:Q ,lcsh:Science ,010306 general physics ,0210 nano-technology ,Bilayer graphene - Abstract
Intrinsic defects give rise to scattering processes governing the transport properties of mesoscopic systems. We investigate analytically and numerically the local density of states in Bernal stacking bilayer graphene with a point defect. With Bernal stacking structure, there are two types of lattice sites. One corresponds to connected sites, where carbon atoms from each layer stack on top of each other, and the other corresponds to disconnected sites. From our theoretical study, a picture emerges in which the pronounced zero-energy peak in the local density of states does not attribute to zero-energy impurity states associated to two different types of defects but to a collective phenomenon of the low-energy resonant states induced by the defect. To corroborate this description, we numerically show that at small system size $N$, where $N$ is the number of unit cells, the zero-energy peak near the defect scales as $1/\ln N$ for the quasi-localized zero-energy state and as $1/N$ for the delocalized zero-energy state. As the system size approaches to the thermodynamic limit, the former zero-energy peak becomes a power-law singularity $1/|E|$ in low energies, while the latter is broadened into a Lorentzian shape. A striking point is that both types of zero-energy peaks decay as $1/r^2$ away from the defect, manifesting the quasi-localized character. Based on our results, we propose a general formula for the local density of states in low-energy and in real space. Our study sheds light on this fundamental problem of defects., Comment: 6 figures. to appear in Sci. Rep
- Published
- 2018
20. Berry curvature dipole current in transition metal dichalcogenides family
- Author
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Su-Yang Xu, Efthimios Kaxiras, Tony Low, Jhih-Shih You, and Shiang Fang
- Subjects
Physics ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Ab initio ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Position and momentum space ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Symmetry (physics) ,Dipole ,Hall effect ,Electric field ,0103 physical sciences ,Displacement field ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Berry connection and curvature ,010306 general physics ,0210 nano-technology - Abstract
We study the quantum nonlinear Hall effect in two-dimensional materials with time-reversal symmetry. When only one mirror line exists, a transverse charge current occurs in second-order response to an external electric field, as a result of the Berry curvature dipole in momentum space. Candidate 2D materials to observe this effect are two-dimensional transition-metal dichalcogenides~(TMDCs). First we use an ab initio based tight-binding approach to demonstrate that monolayer $T_d$-stricture TMDCs exhibit a finite Berry curvature dipole. In the $1H$ and $1T'$ phase of TMDCs, we show the emergence of finite Berry curvature dipole with the application of strain and electrical displacement field respectively., Comment: 4 figures
- Published
- 2018
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21. Symmetry regimes for circular photocurrents in monolayer MoSe2
- Author
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Talieh S. Ghiasi, Jeroen van den Brink, Bart J. van Wees, Jorge Quereda, Caspar H. van der Wal, Jhih-Shih You, and Physics of Nanodevices
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Photon ,Science ,General Physics and Astronomy ,Physics::Optics ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,0103 physical sciences ,Monolayer ,010306 general physics ,Spin (physics) ,lcsh:Science ,Physics ,Condensed Matter - Materials Science ,Multidisciplinary ,SPECTROSCOPY ,Condensed matter physics ,Materials Science (cond-mat.mtrl-sci) ,Charge (physics) ,Biasing ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Symmetry (physics) ,cond-mat.mtrl-sci ,Wavelength ,Computer Science::Programming Languages ,lcsh:Q ,Berry connection and curvature ,0210 nano-technology - Abstract
In monolayer transition metal dichalcogenides helicity-dependent charge and spin photocurrents can emerge, even without applying any electrical bias, due to circular photogalvanic and photon drag effects. Exploiting such circular photocurrents (CPCs) in devices, however, requires better understanding of their behavior and physical origin. Here, we present symmetry, spectral, and electrical characteristics of CPC from excitonic interband transitions in a MoSe2 monolayer. The dependence on bias and gate voltages reveals two different CPC contributions, dominant at different voltages and with different dependence on illumination wavelength and incidence angles. We theoretically analyze symmetry requirements for effects that can yield CPC and compare these with the observed angular dependence and symmetries that occur for our device geometry. This reveals that the observed CPC effects require a reduced device symmetry, and that effects due to Berry curvature of the electronic states do not give a significant contribution.
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- 2018
- Full Text
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22. Unconventional Bose-Einstein condensation in a system with two species of bosons in thep-orbital bands in an optical lattice
- Author
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Jhih-Shih You, Daw-Wei Wang, Congjun Wu, Shih-Chuan Gou, and I-Kang Liu
- Subjects
Condensed Matter::Quantum Gases ,Quantum phase transition ,Physics ,Optical lattice ,Condensed matter physics ,Condensed Matter::Other ,media_common.quotation_subject ,01 natural sciences ,Asymmetry ,010305 fluids & plasmas ,law.invention ,Atomic orbital ,law ,0103 physical sciences ,010306 general physics ,Wave function ,Bose–Einstein condensate ,Lattice model (physics) ,media_common ,Boson - Abstract
In the context of Gross-Pitaevskii theory, we investigate the unconventional Bose-Einstein condensations in the two-species mixture with $p$-wave symmetry in the second band of a bipartite optical lattice. An imaginary-time propagation method is developed to numerically determine the $p$-orbital condensation. Different from the single-species case, the two-species boson mixture exhibits two nonequivalent complex condensates in the intraspecies-interaction-dominating regime, exhibiting the vortex-antivortex lattice configuration in the charge and spin channels, respectively. When the interspecies interaction is tuned across the SU(2) invariant point, the system undergoes a quantum phase transition toward a checkerboardlike spin-density wave state with a real-valued condensate wave function. The influence of lattice asymmetry on the quantum phase transition is addressed. Finally, we present a phase-sensitive measurement scheme for experimentally detecting the unconventional Bose-Einstein condensation in our model.
- Published
- 2016
23. Universal many-body response of heavy impurities coupled to a Fermi sea: a review of recent progress
- Author
-
Dmitri Ivanov, Marko Cetina, Michael Knap, Richard Schmidt, Eugene Demler, and Jhih-Shih You
- Subjects
Physics ,Bosonization ,Quantum decoherence ,General Physics and Astronomy ,Observable ,01 natural sciences ,7. Clean energy ,010305 fluids & plasmas ,Orthogonality ,13. Climate action ,0103 physical sciences ,Statistical physics ,Exponential decay ,010306 general physics ,Fermi gas ,Quantum ,Fermi Gamma-ray Space Telescope - Abstract
In this report we discuss the dynamical response of heavy quantum impurities immersed in a Fermi gas at zero and at finite temperature. Studying both the frequency and the time domain allows one to identify interaction regimes that are characterized by distinct many-body dynamics. From this theoretical study a picture emerges in which impurity dynamics is universal on essentially all time scales, and where the high-frequency few-body response is related to the long-time dynamics of the Anderson orthogonality catastrophe by Tan relations. Our theoretical description relies on different and complementary approaches: functional determinants give an exact numerical solution for time- and frequency-resolved responses, bosonization provides accurate analytical expressions at low temperatures, and the theory of Toeplitz determinants allows one to analytically predict response up to high temperatures. Using these approaches we predict the thermal decoherence rate of the fermionic system and prove that within the considered model the fastest rate of long-time decoherence is given by [Formula: see text]. We show that Feshbach resonances in cold atomic systems give access to new interaction regimes where quantum effects can prevail even in the thermal regime of many-body dynamics. The key signature of this phenomenon is a crossover between different exponential decay rates of the real-time Ramsey signal. It is shown that the physics of the orthogonality catastrophe is experimentally observable up to temperatures [Formula: see text] where it leaves its fingerprint in a power-law temperature dependence of thermal spectral weight and we review how this phenomenon is related to the physics of heavy ions in liquid [Formula: see text]He and the formation of Fermi polarons. The presented results are in excellent agreement with recent experiments on LiK mixtures, and we predict several new phenomena that can be tested using currently available experimental technology.
- Published
- 2018
24. Electron-spin to Phonon Coupling in Graphene Decorated with Heavy Adatoms
- Author
-
Daw-Wei Wang, Miguel A. Cazalilla, and Jhih-Shih You
- Subjects
Superconductivity ,Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Graphene ,Phonon ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Electron ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Lattice (order) ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Condensed Matter::Strongly Correlated Electrons ,Electronic spin ,Spin (physics) - Abstract
The naturally weak spin-orbit coupling in Graphene can be largely enhanced by adatom deposition (e.g. Weeks et al. Phys. Rev. X 1, 021001 (2011)). However, the dynamics of the adatoms also induces a coupling between phonons and the electron spin. Using group theory and a tight-binding model, we systematically investigate the coupling between the low-energy in-plane phonons and the electron spin in single-layer graphene uniformly decorated with heavy adatoms. Our results provide the foundation for future investigations of spin transport and superconductivity in this system. In order to quantify the effect of the coupling to the lattice on the electronic spin dynamics, we compute the spin-flip rate of electrons and holes. We show that the latter exhibits a strong dependence on the quasi-particle energy and system temperature., 16 pages, 5 figures
- Published
- 2015
25. Many-Body Formation and Dissociation of a Dipolar Chain Crystal
- Author
-
Daw-Wei Wang and Jhih-Shih You
- Subjects
Quantum phase transition ,Physics ,Phase boundary ,General Physics and Astronomy ,FOS: Physical sciences ,Dissociation (chemistry) ,Many body ,Dipole ,Chemical physics ,Quantum Gases (cond-mat.quant-gas) ,Lattice (order) ,Compressibility ,Condensed Matter - Quantum Gases ,Quantum fluctuation - Abstract
We propose an experimental scheme to effectively assemble chains of dipolar gases with a uniform length in a multi-layer system. The obtained dipolar chains can form a chain crystal with the system temperature easily controlled by the initial lattice potential and the external field strength during processing. When the density of chains increases, we further observe a second order quantum phase transition for the chain crystal to be dissociated toward layers of 2D crystal, where the quantum fluctuation dominates the classical energy and the compressibility diverges at the phase boundary. The experimental implication of such a dipolar chain crystal and its quantum phase transition is also discussed.
- Published
- 2014
26. Tuning the Kosterlitz-Thouless transition to zero temperature in Anisotropic Boson Systems
- Author
-
Daw-Wei Wang, Miguel A. Cazalilla, Shiang Fang, Jhih-Shih You, Hao Lee, Ministerio de Educación y Ciencia (España), National Science Council (Taiwan), and National Center for Theoretical Sciences (Taiwan)
- Subjects
Physics ,Condensed Matter::Quantum Gases ,Theoretical physics ,Work (thermodynamics) ,Kosterlitz–Thouless transition ,Condensed matter physics ,Quantum Gases (cond-mat.quant-gas) ,FOS: Physical sciences ,Zero temperature ,Anisotropy ,Condensed Matter - Quantum Gases ,Atomic and Molecular Physics, and Optics ,Boson - Abstract
We study the two-dimensional Bose-Hubbard model with anisotropic hopping. Focusing on the effects of anisotropy on superfluid properties such as the helicity modulus and the normal-to-superfluid [Berezinskii-Kosterlitz-Thouless (BKT)] transition temperature, two different approaches are compared: large-scale quantum Monte Carlo simulations and the self-consistent harmonic approximation (SCHA). For the latter, two different formulations are considered, one applying near the isotropic limit and the other applying in the extremely anisotropic limit. Thus we find that the SCHA provides a reasonable description of superfluid properties of this system provided the appropriate type of formulation is employed. The accuracy of the SCHA in the extremely anisotropic limit, where the BKT transition temperature is tuned to zero (i.e., at a quantum critical point) and therefore quantum fluctuations play a dominant role, is particularly striking. © 2012 American Physical Society., This work is supported by NSC grants and also NCTS. M.A.C. gratefully acknowledges the hospitality of NCTS (Taiwan) and the financial support of the Spanish MEC through Grant No. FIS2010-19609-C02-02.
- Published
- 2012
27. Relativistic ferromagnetic magnon at the zigzag edge of graphene
- Author
-
Hsiu-Hau Lin, Jhih-Shih You, and Wen-Min Huang
- Subjects
Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Condensed Matter::Other ,Graphene ,Magnon ,FOS: Physical sciences ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Condensed Matter::Materials Science ,Ferromagnetism ,Zigzag ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Dispersion (optics) ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,Strongly correlated material ,Excitation - Abstract
We study the spin-wave excitations near the zigzag edge of graphene. It is rather interesting that we obtain a single branch of relativistic ferromagnetic magnon due to the presence of the open boundary. Note that magnons in antiferomagnets appear in pairs, while the single brach magnon in ferromagnets does not have relativistic dispersion. Thus, the magnon near the zigzag edge of graphene is a hybrid of both, signaling its intrinsic property as a boundary excitation that must be embedded in a higher dimensional bulk system., 4 pages, 3 figures
- Published
- 2008
28. Infinite Berry Curvature of Weyl Fermi Arcs.
- Author
-
Wawrzik, Dennis, Jhih-Shih You, Facio, Jorge I., van den Brink, Jeroen, and Sodemann, Inti
- Subjects
- *
CURVATURE , *BERRIES , *HALL effect , *BRILLOUIN zones , *SURFACE states - Abstract
We show that Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry curvature scaling as 1/k², where k is the distance to a hot line in the surface Brillouin zone that connects the projection of Weyl nodes with opposite chirality, but which is distinct from the Fermi arc itself. Such surface Berry curvature appears whenever the bulk Weyl dispersion has a velocity tilt toward the surface of interest. This divergence is reflected in a variety of Berry curvature mediated effects that are readily accessible experimentally and, in particular, leads to a surface Berry curvature dipole that grows linearly with the thickness of a slab of a Weyl semimetal material in the limit of the long lifetime of surface states. This implies the emergence of a gigantic contribution to the nonlinear Hall effect in such devices. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
29. Tuning the Kosterlitz-Thouless transition to zero temperature in anisotropic boson systems.
- Author
-
Jhih-Shih You, Hao Lee, Shiang Fang, Cazalilla, Miguel A., and Daw-Wei Wang
- Subjects
- *
ANISOTROPY , *BOSONS , *SUPERFLUIDITY , *MONTE Carlo method , *PHASE transitions , *CRITICAL point (Thermodynamics) , *FLUCTUATIONS (Physics) , *QUANTUM theory - Abstract
We study the two-dimensional Bose-Hubbard model with anisotropic hopping. Focusing on the effects of anisotropy on superfluid properties such as the helicity modulus and the normal-to-superfiuid [Berezinskii-Kosterlitz-Thouless (BKT)] transition temperature, two different approaches are compared: large-scale quantum Monte Carlo simulations and the self-consistent harmonic approximation (SCHA). For the latter, two different formulations are considered, one applying near the isotropic limit and the other applying in the extremely anisotropic limit. Thus we find that the SCHA provides a reasonable description of superfluid properties of this system provided the appropriate type of formulation is employed. The accuracy of the SCHA in the extremely anisotropic limit, where the BKT transition temperature is tuned to zero (i.e., at a quantum critical point) and therefore quantum fluctuations play a dominant role, is particularly striking. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
30. Universal many-body response of heavy impurities coupled to a Fermi sea: a review of recent progress.
- Author
-
Richard Schmidt, Michael Knap, Dmitri A Ivanov, Jhih-Shih You, Marko Cetina, and Eugene Demler
- Subjects
ELECTRON gas ,FERMIONS ,PARTICLES (Nuclear physics) ,LEPTONS (Nuclear physics) ,INTERACTING boson-fermion models - Abstract
In this report we discuss the dynamical response of heavy quantum impurities immersed in a Fermi gas at zero and at finite temperature. Studying both the frequency and the time domain allows one to identify interaction regimes that are characterized by distinct many-body dynamics. From this theoretical study a picture emerges in which impurity dynamics is universal on essentially all time scales, and where the high-frequency few-body response is related to the long-time dynamics of the Anderson orthogonality catastrophe by Tan relations. Our theoretical description relies on different and complementary approaches: functional determinants give an exact numerical solution for time- and frequency-resolved responses, bosonization provides accurate analytical expressions at low temperatures, and the theory of Toeplitz determinants allows one to analytically predict response up to high temperatures. Using these approaches we predict the thermal decoherence rate of the fermionic system and prove that within the considered model the fastest rate of long-time decoherence is given by . We show that Feshbach resonances in cold atomic systems give access to new interaction regimes where quantum effects can prevail even in the thermal regime of many-body dynamics. The key signature of this phenomenon is a crossover between different exponential decay rates of the real-time Ramsey signal. It is shown that the physics of the orthogonality catastrophe is experimentally observable up to temperatures where it leaves its fingerprint in a power-law temperature dependence of thermal spectral weight and we review how this phenomenon is related to the physics of heavy ions in liquid He and the formation of Fermi polarons. The presented results are in excellent agreement with recent experiments on LiK mixtures, and we predict several new phenomena that can be tested using currently available experimental technology. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
31. Electron-spin to phonon coupling in graphene decorated with heavy adatoms.
- Author
-
Jhih-Shih You, Daw-Wei Wang, and Cazalilla, Miguel A.
- Subjects
- *
ELECTRON spin , *GRAPHENE , *ADATOMS , *SUPERCONDUCTIVITY , *QUASIPARTICLES - Abstract
The naturally weak spin-orbit coupling in graphene can be largely enhanced by adatom deposition [e.g., Weeks et al., Phys. Rev. X 1, 021001 (2011)]. However, the dynamics of the adatoms also induces a coupling between phonons and the electron spin. Using group theory and a tight-binding model, we systematically investigate the coupling between the low-energy in-plane phonons and the electron spin in single-layer graphene uniformly decorated with heavy adatoms. Our results provide the foundation for future investigations of spin transport and superconductivity in this system. In order to quantify the effect of the coupling to the lattice on the electronic spin dynamics, we compute the spin-flip rate of electrons and holes. We show that the latter exhibits a strong dependence on the quasiparticle energy and system temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
32. Unconventional Bose-Einstein condensation in a system with two species of bosons in the p-orbital bands in an optical lattice.
- Author
-
Jhih-Shih You, I-Kang Liu, Daw-Wei Wang, Shih-Chuan Gou, and Congjun Wu
- Subjects
- *
BOSE-Einstein condensation , *BOSONS , *OPTICAL lattices - Abstract
In the context of Gross-Pitaevskii theory, we investigate the unconventional Bose-Einstein condensations in the two-species mixture with p-wave symmetry in the second band of a bipartite optical lattice. An imaginary-time propagation method is developed to numerically determine the p-orbital condensation. Different from the single-species case, the two-species boson mixture exhibits two nonequivalent complex condensates in the intraspecies-interaction-dominating regime, exhibiting the vortex-antivortex lattice configuration in the charge and spin channels, respectively. When the interspecies interaction is tuned across the SU(2) invariant point, the system undergoes a quantum phase transition toward a checkerboardlike spin-density wave state with a real-valued condensate wave function. The influence of lattice asymmetry on the quantum phase transition is addressed. Finally, we present a phase-sensitive measurement scheme for experimentally detecting the unconventional Bose-Einstein condensation in our model. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
33. Strongly Enhanced Berry Dipole at Topological Phase Transitions in BiTeI.
- Author
-
Facio, Jorge I., Efremov, Dmitri, Koepernik, Klaus, Jhih-Shih You, Sodemann, Inti, and van den Brink, Jeroen
- Subjects
- *
TOPOLOGY , *PHASE transitions , *BISMUTH compounds - Abstract
Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here, we focus on the giant Rashba material bismuth tellurium iodine which exhibits a pressure-driven phase transition between topological and trivial insulators in three dimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semimetallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berry dipole--a vector along the polar axis of this material--has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points, at which the nonlinear Hall conductivity can increase by over 2 orders of magnitude. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
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