scholarly journals Boundary conductance in macroscopic bismuth crystals

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Woun Kang ◽  
Felix Spathelf ◽  
Benoît Fauqué ◽  
Yuki Fuseya ◽  
Kamran Behnia
Keyword(s):  
Quantum Hall ◽  
Three Dimensional ◽  
Surface States ◽  
Metallic Surface ◽  
Periodically Driven ◽  
Dimensional Boundary ◽  
Intimate Link ◽  
Different Shapes ◽  
The Magnetic Field ◽  
Identical Crystal

AbstractThe interface between a solid and vacuum can become electronically distinct from the bulk. This feature, encountered in the case of quantum Hall effect, has a manifestation in insulators with topologically protected metallic surface states. Non-trivial Berry curvature of the Bloch waves or periodically driven perturbation are known to generate it. Here, by studying the angle-dependent magnetoresistance in prismatic bismuth crystals of different shapes, we detect a robust surface contribution to electric conductivity when the magnetic field is aligned parallel to a two-dimensional boundary between the three-dimensional crystal and vacuum. The effect is absent in antimony, which has an identical crystal symmetry, a similar Fermi surface structure and equally ballistic carriers, but an inverted band symmetry and a topological invariant of opposite sign. Our observation confirms that the boundary interrupting the cyclotron orbits remains metallic in bismuth, which is in agreement with what was predicted by Azbel decades ago. However, the absence of the effect in antimony indicates an intimate link between band symmetry and this boundary conductance.

scholarly journals Boundary conductance protected by topology in macroscopic bismuth crystals

2021 ◽  
Author(s):  
Woun Kang ◽  
Felix Spathelf ◽  
Benoit Fauqué ◽  
Yuki Fuseya ◽  
Kamran Behnia
Keyword(s):  
Quantum Hall ◽  
Three Dimensional ◽  
Surface States ◽  
Metallic Surface ◽  
Periodically Driven ◽  
Dimensional Boundary ◽  
Different Shapes ◽  
The Magnetic Field ◽  
Dimensional Crystal ◽  
Identical Crystal

Abstract The interface between a solid and vacuum can become electronically distinct from the bulk. This feature, encountered in the case of quantum Hall effect, has a manifestation in insulators with topologically protected metallic surface states. Non-trivial Berry curvature of the Bloch waves or periodically driven perturbation are known to generate it. Here, by studying the angle-dependent magnetoresistance in prismatic bismuth crystals of different shapes, we detect a robust surface contribution to electric conductivity when the magnetic field is aligned parallel to a two-dimensional boundary between the three-dimensional crystal and vacuum. The effect is absent in antimony, which has an identical crystal symmetry, a similar Fermi surface structure and equally ballistic carriers, but an inverted band symmetry and a topological invariant of opposite sign. Our observation points to the relevance of band symmetries to survival of metallicity at the boundary interrupting the cyclotron orbits.

scholarly journals Electron–hole asymmetry of the topological surface states in strained HgTe

2017 ◽  
Vol 114 (13) ◽  
pp. 3381-3386 ◽  
Author(s):  
Andreas Jost ◽  
Michel Bendias ◽  
Jan Böttcher ◽  
Ewelina Hankiewicz ◽  
Christoph Brüne ◽  
...  
Keyword(s):  
Topological Insulators ◽  
Quantum Hall ◽  
Surface States ◽  
Metallic Surface ◽  
Electron Hole ◽  
Linear Dispersion ◽  
Strong Electron ◽  
Quantum Oscillations ◽  
Strong Deviation ◽  
Topological Surface

Topological insulators are a new class of materials with an insulating bulk and topologically protected metallic surface states. Although it is widely assumed that these surface states display a Dirac-type dispersion that is symmetric above and below the Dirac point, this exact equivalence across the Fermi level has yet to be established experimentally. Here, we present a detailed transport study of the 3D topological insulator-strained HgTe that strongly challenges this prevailing viewpoint. First, we establish the existence of exclusively surface-dominated transport via the observation of an ambipolar surface quantum Hall effect and quantum oscillations in the Seebeck and Nernst effect. Second, we show that, whereas the thermopower is diffusion driven for surface electrons, both diffusion and phonon drag contributions are essential for the hole surface carriers. This distinct behavior in the thermoelectric response is explained by a strong deviation from the linear dispersion relation for the surface states, with a much flatter dispersion for holes compared with electrons. These findings show that the metallic surface states in topological insulators can exhibit both strong electron–hole asymmetry and a strong deviation from a linear dispersion but remain topologically protected.

scholarly journals Intrinsic coupling between spatially-separated surface Fermi-arcs in Weyl orbit quantum Hall states

2020 ◽  
Author(s):  
Shinichi Nishihaya ◽  
Masaki Uchida ◽  
Yusuke Nakazawa ◽  
Markus Kriener ◽  
Yasujiro Taguchi ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Recent Observation ◽  
Quantum Hall ◽  
Three Dimensional ◽  
Surface States ◽  
Back Gate ◽  
Fermi Arc ◽  
Quantum Hall States ◽  
Topological Semimetals ◽  
Hall States

Abstract Topological semimetals hosting bulk Weyl points and surface Fermi-arc states are expected to realize unconventional Weyl orbits, which interconnect two surface Fermi-arc states on opposite sample surfaces under magnetic fields. While the presence of Weyl orbits has been proposed to play a vital role in recent observation of quantum Hall effect even in three-dimensional topological semimetals, actual spatial distribution of the quantized surface transport has been experimentally elusive. Here, we demonstrate intrinsic coupling between two spatially-separated surface states in the Weyl orbits by measuring a dual-gate device of a Dirac semimetal film. Independent scans of top- and back-gate voltages reveal concomitant modulation of doubly-degenerate quantum Hall states, which is not possible in conventional surface orbits as in topological insulators. Our results evidencing the unique spatial distribution of Weyl orbits provide new opportunities for controlling the novel quantized transport by various means such as external fields and interface engineering.

Broken-symmetry states in topological insulators

2015 ◽  
Vol 29 (25) ◽  
pp. 1530006
Author(s):  
Yihua Wang
Keyword(s):  
Three Dimensional ◽  
Surface States ◽  
Magnetic Monopoles ◽  
Broken Symmetry ◽  
Metallic Surface ◽  
Photoemission Spectroscopy ◽  
Majorana Fermions ◽  
Magnetic Structures ◽  
Light Pulses ◽  
Fundamental Particles

Breaking the time-reversal symmetry (TRS) on the surface of a three-dimensional topological insulator (TI) transforms its metallic surface into a Chern insulator. The TRS-broken surface states are essential for many exotic emergent particles in condensed matter. In this review, I will show broken TRS surface states of TI induced by magnetism and by light imaged with scanning microscopy and photoemission spectroscopy, respectively. Our capability to manipulate mesoscopic magnetic structures as well as to shape ultrafast light pulses makes broken-symmetry states in TI promising platforms to simulate elusive fundamental particles such as magnetic monopoles and Majorana fermions.

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