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James Analytis - One of the best experts on this subject based on the ideXlab platform.
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transport evidence for fermi arc mediated chirality transfer in the dirac semimetal cd3as2
Nature, 2016Co-Authors: Philip J W Moll, James Analytis, Ashvin Vishwanath, Nityan Nair, Toni Helm, Andrew C Potter, Itamar KimchiAbstract:Electronic transport measurements in a magnetic field on the topological Dirac semimetal Cd3As2 identify the predicted Weyl orbits that weave Fermi arcs and bulk states together; the Weyl orbits enable transfer of chirality from one node to another, and open up the possibility of controlling topological properties electronically. In recently discovered topological semimetals, quasiparticles appear that are condensed-matter versions of high-energy massless Weyl fermions. They show curious electronic behaviour, having a distinct chirality and residing in topologically Protected states. At the Surface, so-called Fermi arcs form between specific Weyl nodes, and these have recently been observed in spectroscopic measurements. Philip Moll et al. present electronic transport measurements of the topological Dirac semimetal Cd3As2 in a magnetic field, identifying the predicted Weyl orbits that weave Fermi arcs and bulk states together. These Weyl orbits enable transfer of chirality from one node to another and open up the possibility of controlling topological properties electronically. The dispersion of charge carriers in a metal is distinctly different from that of free electrons owing to their interactions with the crystal lattice. These interactions may lead to quasiparticles mimicking the massless relativistic dynamics of high-energy particle physics1,2,3, and they can twist the quantum phase of electrons into topologically non-trivial knots—producing Protected Surface states with anomalous electromagnetic properties4,5,6,7,8,9. These effects intertwine in materials known as Weyl semimetals, and in their crystal-symmetry-Protected analogues, Dirac semimetals10. The latter show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation (a theoretical description of massless relativistic fermions). At the Surface of a crystal, the broken translational symmetry creates topological Surface states, so-called Fermi arcs11, which have no counterparts in high-energy physics or conventional condensed matter systems. Here we present Shubnikov–de Haas oscillations in focused-ion-beam-prepared microstructures of Cd3As2 that are consistent with the theoretically predicted ‘Weyl orbits’, a kind of cyclotron motion that weaves together Fermi-arc and chiral bulk states12. In contrast to conventional cyclotron orbits, this motion is driven by the transfer of chirality from one Weyl node to another, rather than momentum transfer of the Lorentz force. Our observations provide evidence for direct access to the topological properties of charge in a transport experiment, a first step towards their potential application.
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transport evidence for fermi arc mediated chirality transfer in the dirac semimetal cd3as2
Nature, 2016Co-Authors: Philip J W Moll, James Analytis, Ashvin Vishwanath, Nityan Nair, Toni Helm, Andrew C Potter, Itamar KimchiAbstract:The dispersion of charge carriers in a metal is distinctly different from that of free electrons owing to their interactions with the crystal lattice. These interactions may lead to quasiparticles mimicking the massless relativistic dynamics of high-energy particle physics, and they can twist the quantum phase of electrons into topologically non-trivial knots-producing Protected Surface states with anomalous electromagnetic properties. These effects intertwine in materials known as Weyl semimetals, and in their crystal-symmetry-Protected analogues, Dirac semimetals. The latter show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation (a theoretical description of massless relativistic fermions). At the Surface of a crystal, the broken translational symmetry creates topological Surface states, so-called Fermi arcs, which have no counterparts in high-energy physics or conventional condensed matter systems. Here we present Shubnikov-de Haas oscillations in focused-ion-beam-prepared microstructures of Cd3As2 that are consistent with the theoretically predicted 'Weyl orbits', a kind of cyclotron motion that weaves together Fermi-arc and chiral bulk states. In contrast to conventional cyclotron orbits, this motion is driven by the transfer of chirality from one Weyl node to another, rather than momentum transfer of the Lorentz force. Our observations provide evidence for direct access to the topological properties of charge in a transport experiment, a first step towards their potential application.
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stm imaging of electronic waves on the Surface of bi2te3 topologically Protected Surface states and hexagonal warping effects
Physical Review Letters, 2010Co-Authors: Zhanybek Alpichshev, James Analytis, Jiunhaw Chu, I R Fisher, Yulin ChenAbstract:Scanning tunneling spectroscopy studies on high-quality Bi2Te3 crystals exhibit perfect correspondence to angle-resolved photoemission spectroscopy data, hence enabling identification of different regimes measured in the local density of states (LDOS). Oscillations of LDOS near a step are analyzed. Within the main part of the Surface band oscillations are strongly damped, supporting the hypothesis of topological protection. At higher energies, as the Surface band becomes concave, oscillations appear, dispersing with a wave vector that may result from a hexagonal warping term.
Steven G Louie - One of the best experts on this subject based on the ideXlab platform.
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quasiparticle effects in the bulk and Surface state bands of bi 2 se 3 and bi 2 te 3 topological insulators
Physical Review B, 2012Co-Authors: Oleg V Yazyev, Joel E Moore, Steven G Louie, Emmanouil KioupakisAbstract:We investigate the bulk band structures and the Surface states of Bi2Se3 and Bi2Te3 topological insulators using first-principles many-body perturbation theory based on the GW approximation. The quasiparticle self-energy corrections introduce significant changes to the bulk band structures, surprisingly leading to a decrease in the direct band gaps in the band-inversion regime as opposed to the usual situation without band inversion. Parametrized "scissors operators" derived from the bulk studies are then used to investigate the electronic structure of slab models which exhibit topologically Protected Surface states. The introduction of self-energy corrections results in significant shifts of the Surface-state Dirac point energies relative to the bulk bands and in enlarged gap openings from the interactions between the Surface states across the thin slab, both in agreement with experimental data.
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spin polarization and transport of Surface states in the topological insulators bi2se3 and bi2te3 from first principles
Physical Review Letters, 2010Co-Authors: Oleg V Yazyev, Joel E Moore, Steven G LouieAbstract:We investigate the band dispersion and the spin texture of topologically Protected Surface states in the bulk topological insulators ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ and ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ by first-principles methods. Strong spin-orbit entanglement in these materials reduces the spin polarization of the Surface states to $\ensuremath{\sim}50%$ in both cases; this reduction is absent in simple models but of important implications to essentially any spintronic application. We propose a way of controlling the magnitude of spin polarization associated with a charge current in thin films of topological insulators by means of an external electric field. The proposed dual-gate device configuration provides new possibilities for electrical control of spin.
Oleg V Yazyev - One of the best experts on this subject based on the ideXlab platform.
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quasiparticle effects in the bulk and Surface state bands of bi 2 se 3 and bi 2 te 3 topological insulators
Physical Review B, 2012Co-Authors: Oleg V Yazyev, Joel E Moore, Steven G Louie, Emmanouil KioupakisAbstract:We investigate the bulk band structures and the Surface states of Bi2Se3 and Bi2Te3 topological insulators using first-principles many-body perturbation theory based on the GW approximation. The quasiparticle self-energy corrections introduce significant changes to the bulk band structures, surprisingly leading to a decrease in the direct band gaps in the band-inversion regime as opposed to the usual situation without band inversion. Parametrized "scissors operators" derived from the bulk studies are then used to investigate the electronic structure of slab models which exhibit topologically Protected Surface states. The introduction of self-energy corrections results in significant shifts of the Surface-state Dirac point energies relative to the bulk bands and in enlarged gap openings from the interactions between the Surface states across the thin slab, both in agreement with experimental data.
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spin polarization and transport of Surface states in the topological insulators bi2se3 and bi2te3 from first principles
Physical Review Letters, 2010Co-Authors: Oleg V Yazyev, Joel E Moore, Steven G LouieAbstract:We investigate the band dispersion and the spin texture of topologically Protected Surface states in the bulk topological insulators ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ and ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ by first-principles methods. Strong spin-orbit entanglement in these materials reduces the spin polarization of the Surface states to $\ensuremath{\sim}50%$ in both cases; this reduction is absent in simple models but of important implications to essentially any spintronic application. We propose a way of controlling the magnitude of spin polarization associated with a charge current in thin films of topological insulators by means of an external electric field. The proposed dual-gate device configuration provides new possibilities for electrical control of spin.
Ashvin Vishwanath - One of the best experts on this subject based on the ideXlab platform.
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shift insulators rotation Protected two dimensional topological crystalline insulators
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Shang Liu, Ashvin Vishwanath, Eslam KhalafAbstract:We study a two-dimensional (2D) tight-binding model of a topological crystalline insulator (TCI) Protected by rotation symmetry. The model is built by stacking two Chern insulators with opposite Chern numbers which transform under conjugate representations of the rotation group, e.g. $p_\pm$ orbitals. Despite its apparent similarity to the Kane-Mele model, it does not host stable gapless Surface states. Nevertheless the model exhibits topological responses including the appearance of quantized fractional charge bound to rotational defects (disclinations) and the pumping of angular momentum in response to threading an elementary magnetic flux, which are described by a mutual Chern-Simons coupling between the electromagnetic gauge field and an effective gauge field corresponding to the rotation symmetry. In addition, we show that although the filled bands of the model do not admit a symmetric Wannier representation, this obstruction is removed upon the addition of appropriate atomic orbitals, which implies `fragile' topology. As a result, the response of the model can be derived by representing it as a superposition of atomic orbitals with positive and negative integer coefficients. Following the analysis of the model, which serves as a prototypical example of 2D TCIs Protected by rotation, we show that all TCIs Protected by point group symmetries which do not have Protected Surface states are either atomic insulators or fragile phases. Remarkably, this implies that gapless Surface states exist in free electron systems if and only if there is a stable Wannier obstruction. We then use dimensional reduction to map the problem of classifying 2D TCIs Protected by rotation to a zero-dimensional (0D) problem which is then used to obtain the complete non-interacting classification of such TCIs as well as the reduction of this classification in the presence of interactions.
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weyl and dirac semimetals in three dimensional solids
Reviews of Modern Physics, 2018Co-Authors: N P Armitage, E J Mele, Ashvin VishwanathAbstract:Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are Protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to Protected Surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.
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symmetry based indicators of band topology in the 230 space groups
Nature Communications, 2017Co-Authors: Ashvin Vishwanath, Hoi Chun Po, Haruki WatanabeAbstract:The interplay between symmetry and topology leads to a rich variety of electronic topological phases, protecting states such as the topological insulators and Dirac semimetals. Previous results, like the Fu-Kane parity criterion for inversion-symmetric topological insulators, demonstrate that symmetry labels can sometimes unambiguously indicate underlying band topology. Here we develop a systematic approach to expose all such symmetry-based indicators of band topology in all the 230 space groups. This is achieved by first developing an efficient way to represent band structures in terms of elementary basis states, and then isolating the topological ones by removing the subset of atomic insulators, defined by the existence of localized symmetric Wannier functions. Aside from encompassing all earlier results on such indicators, including in particular the notion of filling-enforced quantum band insulators, our theory identifies symmetry settings with previously hidden forms of band topology, and can be applied to the search for topological materials. Understanding the role of topology in determining electronic structure can lead to the discovery, or appreciation, of materials with exotic properties such as Protected Surface states. Here, the authors present a framework for identifying topologically distinct band-structures for all 3D space groups.
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transport evidence for fermi arc mediated chirality transfer in the dirac semimetal cd3as2
Nature, 2016Co-Authors: Philip J W Moll, James Analytis, Ashvin Vishwanath, Nityan Nair, Toni Helm, Andrew C Potter, Itamar KimchiAbstract:The dispersion of charge carriers in a metal is distinctly different from that of free electrons owing to their interactions with the crystal lattice. These interactions may lead to quasiparticles mimicking the massless relativistic dynamics of high-energy particle physics, and they can twist the quantum phase of electrons into topologically non-trivial knots-producing Protected Surface states with anomalous electromagnetic properties. These effects intertwine in materials known as Weyl semimetals, and in their crystal-symmetry-Protected analogues, Dirac semimetals. The latter show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation (a theoretical description of massless relativistic fermions). At the Surface of a crystal, the broken translational symmetry creates topological Surface states, so-called Fermi arcs, which have no counterparts in high-energy physics or conventional condensed matter systems. Here we present Shubnikov-de Haas oscillations in focused-ion-beam-prepared microstructures of Cd3As2 that are consistent with the theoretically predicted 'Weyl orbits', a kind of cyclotron motion that weaves together Fermi-arc and chiral bulk states. In contrast to conventional cyclotron orbits, this motion is driven by the transfer of chirality from one Weyl node to another, rather than momentum transfer of the Lorentz force. Our observations provide evidence for direct access to the topological properties of charge in a transport experiment, a first step towards their potential application.
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transport evidence for fermi arc mediated chirality transfer in the dirac semimetal cd3as2
Nature, 2016Co-Authors: Philip J W Moll, James Analytis, Ashvin Vishwanath, Nityan Nair, Toni Helm, Andrew C Potter, Itamar KimchiAbstract:Electronic transport measurements in a magnetic field on the topological Dirac semimetal Cd3As2 identify the predicted Weyl orbits that weave Fermi arcs and bulk states together; the Weyl orbits enable transfer of chirality from one node to another, and open up the possibility of controlling topological properties electronically. In recently discovered topological semimetals, quasiparticles appear that are condensed-matter versions of high-energy massless Weyl fermions. They show curious electronic behaviour, having a distinct chirality and residing in topologically Protected states. At the Surface, so-called Fermi arcs form between specific Weyl nodes, and these have recently been observed in spectroscopic measurements. Philip Moll et al. present electronic transport measurements of the topological Dirac semimetal Cd3As2 in a magnetic field, identifying the predicted Weyl orbits that weave Fermi arcs and bulk states together. These Weyl orbits enable transfer of chirality from one node to another and open up the possibility of controlling topological properties electronically. The dispersion of charge carriers in a metal is distinctly different from that of free electrons owing to their interactions with the crystal lattice. These interactions may lead to quasiparticles mimicking the massless relativistic dynamics of high-energy particle physics1,2,3, and they can twist the quantum phase of electrons into topologically non-trivial knots—producing Protected Surface states with anomalous electromagnetic properties4,5,6,7,8,9. These effects intertwine in materials known as Weyl semimetals, and in their crystal-symmetry-Protected analogues, Dirac semimetals10. The latter show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation (a theoretical description of massless relativistic fermions). At the Surface of a crystal, the broken translational symmetry creates topological Surface states, so-called Fermi arcs11, which have no counterparts in high-energy physics or conventional condensed matter systems. Here we present Shubnikov–de Haas oscillations in focused-ion-beam-prepared microstructures of Cd3As2 that are consistent with the theoretically predicted ‘Weyl orbits’, a kind of cyclotron motion that weaves together Fermi-arc and chiral bulk states12. In contrast to conventional cyclotron orbits, this motion is driven by the transfer of chirality from one Weyl node to another, rather than momentum transfer of the Lorentz force. Our observations provide evidence for direct access to the topological properties of charge in a transport experiment, a first step towards their potential application.
L Krusinelbaum - One of the best experts on this subject based on the ideXlab platform.
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bulk defects and Surface state dynamics in topological insulators the effects of electron beam irradiation on the ultrafast relaxation of dirac fermions in bi 2 te 3
Journal of Applied Physics, 2019Co-Authors: Lama Khalil, Evangelos Papalazarou, M Caputo, N Nilforoushan, Luca Perfetti, A Talebibrahimi, M Konczykowski, Andrzej Hruban, Agnieszka Woloś, L KrusinelbaumAbstract:One of the most important challenges in the study of topological insulators is the realization of materials that are really insulating in the bulk, in order to emphasize quantum transport in the Protected Surface states. Irradiation with electron beams is a very promising approach toward this goal. By studying a series of samples of the prototype 3D topological insulator Bi 2 Te 3, we show that while the topological properties of Dirac Surface states are preserved after electron irradiation, their relaxation dynamics are very sensitive to the related modifications of the bulk properties. Using time- and angle-resolved photoelectron spectroscopy, we can reveal two distinct relaxation regimes after optical excitation for non-irradiated and irradiated samples. While the faster regime, corresponding to the first few picoseconds, presents a similar temporal evolution of the photoexcited population for all studied samples, the slower regime is strongly influenced by the controlled generation of defects in the bulk lattice. By adjusting the irradiation parameters in this class of materials, one can thus not only change the bulk transport properties but also tune the ultrafast response of the topological Surface states.One of the most important challenges in the study of topological insulators is the realization of materials that are really insulating in the bulk, in order to emphasize quantum transport in the Protected Surface states. Irradiation with electron beams is a very promising approach toward this goal. By studying a series of samples of the prototype 3D topological insulator Bi 2 Te 3, we show that while the topological properties of Dirac Surface states are preserved after electron irradiation, their relaxation dynamics are very sensitive to the related modifications of the bulk properties. Using time- and angle-resolved photoelectron spectroscopy, we can reveal two distinct relaxation regimes after optical excitation for non-irradiated and irradiated samples. While the faster regime, corresponding to the first few picoseconds, presents a similar temporal evolution of the photoexcited population for all studied samples, the slower regime is strongly influenced by the controlled generation of defects in...
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bulk defects and Surface state dynamics in topological insulators the effects of electron beam irradiation on the ultrafast relaxation of dirac fermions in bi 2 te 3
Journal of Applied Physics, 2019Co-Authors: Lama Khalil, Evangelos Papalazarou, M Caputo, N Nilforoushan, Luca Perfetti, A Talebibrahimi, M Konczykowski, Andrzej Hruban, Agnieszka Woloś, L KrusinelbaumAbstract:One of the most important challenges in the study of topological insulators is the realization of materials that are really insulating in the bulk, in order to emphasize quantum transport in the Protected Surface states. Irradiation with electron beams is a very promising approach toward this goal. By studying a series of samples of the prototype 3D topological insulator Bi 2 Te 3, we show that while the topological properties of Dirac Surface states are preserved after electron irradiation, their relaxation dynamics are very sensitive to the related modifications of the bulk properties. Using time- and angle-resolved photoelectron spectroscopy, we can reveal two distinct relaxation regimes after optical excitation for non-irradiated and irradiated samples. While the faster regime, corresponding to the first few picoseconds, presents a similar temporal evolution of the photoexcited population for all studied samples, the slower regime is strongly influenced by the controlled generation of defects in the bulk lattice. By adjusting the irradiation parameters in this class of materials, one can thus not only change the bulk transport properties but also tune the ultrafast response of the topological Surface states.
