Evidence for Topological Edge States in a Large Energy Gap near the Step Edges on the Surface of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>ZrTe</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Wu, Rongting; Ma, Junzhang; Nie, Simin; Zhao, Lingxiao; Huang, Xuejie; Yin, Jiaxin; Bao, Futing; Richard, P.; Chen, Gengfu; Fang, Zhong; Dai, Xi; Weng, Hongming; Qian, Tian; Ding, Hong; Pan, S. H.

doi:10.1103/physrevx.6.021017

Cited by 168 publications

(254 citation statements)

References 35 publications

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“…As will be shown below, the resistivity peak and the thermopower sign reversal at T p can be reproduced by our parameter-free transport calculations when taking into account the intrinsic band structure anisotropies at the valence band maximum and conduction band minimum. Our results also provide a simple physical explanation for the contradictory reports in the literature regarding the electronic structure of ZrTe 5 , i.e., semiconductor versus Dirac semimetal [12][13][14][15][16][17][18].…”

Section: Carrier Density and Mobilitysupporting

confidence: 59%

“…The ZrTe 5 single crystals used in the present study were grown by chemical vapor transport for the CVT samples [16] and by the Te-flux method for the Flux samples [18]. We employed iodine (I 2 ) as the transport agent during the CVT crystal growth.…”

Section: A Crystal Growthmentioning

confidence: 99%

“…More recently, these compounds have become of interest as topological materials whose low-energy electronic structure is controlled by spin-orbit interactions [11]. Nevertheless, it is currently under hot debate whether they are insulators or Dirac semimetals [6,[12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

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Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior

et al. 2018

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The pentatellurides ZrTe 5 and HfTe 5 are layered compounds with one-dimensional transition-metal chains that show a not-yet-understood temperature-dependent transition in transport properties as well as recently discovered properties suggesting topological semimetallic behavior. Here, we report magnetotransport properties for two kinds of ZrTe 5 single crystals grown with the chemical vapor transport (CVT) and the flux method (Flux), respectively. They show distinct transport properties at zero field: The CVT crystal displays a metallic behavior with a pronounced resistance peak and a sudden sign reversal in thermopower at approximately 130 K, consistent with previous observations of the electronic transition; in striking contrast, the Flux crystal exhibits a semiconducting-like behavior at low temperatures and a positive thermopower over the whole temperature range. For both samples, strong effects on the transport properties are observed when the magnetic field is applied along the orthorhombic b and c axes, i.e., perpendicular to the chain direction. Refinements on the single-crystal x-ray diffraction and the measurements of energy dispersive spectroscopy reveal the presence of noticeable Te vacancies in the CVT samples, while the Flux samples are close to the stoichiometry. Analyses on the magnetotransport properties confirm that the carrier densities of the CVT sample are about two orders higher than those of the Flux sample. Our results thus indicate that the widely observed anomalous transport behaviors in pentatellurides actually take place in the Te-deficient samples. For the stoichiometric pentatellurides, our electronic structure calculations show narrow-gap semiconducting behavior, with different transport anisotropies for holes and electrons. For the degenerately doped n-type samples, our transport calculations can result in a resistivity peak and crossover in thermopower from negative to positive at temperatures close to those observed experimentally due to a combination of bipolar effects and different anisotropies of electrons and holes. Our present work resolves the long-standing puzzle regarding the anomalous transport behaviors of pentatellurides, as well as the electronic structure in favor of a semiconducting state.

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Section: Carrier Density and Mobilitysupporting

confidence: 59%

Section: A Crystal Growthmentioning

confidence: 99%

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Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior

et al. 2018

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“…3 (e), displaying the SX photon energy scan for LV polarization. In this dataset the binding energy of the CEM is −50 meV, which corresponds to the same energy position of panel (a) with respect of the band structure, owing to the temperature dependent energy shift of the band structure [15,19], (see suppl. information [26]).…”

mentioning

confidence: 67%

Evidence for a Strong Topological Insulator Phase in ZrTe5

et al. 2016

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The complex electronic properties of ZrTe5 have recently stimulated in-depth investigations that assigned this material to either a topological insulator or a 3D Dirac semimetal phase. Here we report a comprehensive experimental and theoretical study of both electronic and structural properties of ZrTe5, revealing that the bulk material is a strong topological insulator (STI). By means of angle-resolved photoelectron spectroscopy, we identify at the top of the valence band both a surface and a bulk state. The dispersion of these bands is well captured by ab initio calculations for the STI case, for the specific interlayer distance measured in our x-ray diffraction study. Furthermore, these findings are supported by scanning tunneling spectroscopy revealing the metallic character of the sample surface, thus confirming the strong topological nature of ZrTe5.The discovery of topological insulators (TIs), characterized by metallic spin-polarized surface states connecting the bulk valence and conduction bands [1], has stimulated the search for novel topological phases of matter [2][3][4][5][6]. ZrTe 5 has recently emerged as a challenging system with unique, albeit poorly understood, electronic properties [7][8][9][10][11][12][13][14][15][16][17]. Magneto-transport [11], magneto-infrared [13] and optical spectroscopy [14] studies describe ZrTe 5 in terms of a 3D Dirac semimetal. Theoretical calculations have predicted its bulk electronic properties to lie in proximity of a topological phase transition between a strong and a weak TI (STI and WTI, respectively), where only the former displays topologically protected surface states at the experimentally accessible (010) surface [10]. The monolayer is also computed to be a 2D TI [10] and scanning tunneling microscopy/spectroscopy (STM/STS) experiments suggest the existence of topologically protected states at step edges [18,19]. However, the unambiguous identification of the topological phase of ZrTe 5 is still lacking.In this Letter we report on the STI character of the bulk ZrTe 5 by combining ab initio calculations and multiple experimental techniques, at temperature both above and below the one of the resistivity peak, T * ∼ 160 K [7][8][9]15]. Angleresolved photoelectron spectroscopy (ARPES) experiments in the ultraviolet (UV) and soft x-ray (SX) energy ranges reveal the presence of two distinct states at the top of the valence band (VB). On the basis of photon energy dependent studies, we ascribe the origin of these two states to the bulk and crystal surface, respectively. We have performed ab initio calculations of the topological phase diagram of ZrTe 5 , as a function of the interlayer distance b/2. Our measured band dispersion is in agreement with the calculations and it is consistent with the STI case for b/2 = 7.23 ± 0.02Å. This value has been confirmed for our specimen by x-ray diffraction (XRD) measurements. Furthermore, the 3D Dirac semimetal phase is not protected by crystalline symmetries, and it manifests only for the specific b/2 = 7.35Å at the boundar...

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“…There the interpretation was that ZrTe 5 is a Dirac semimetal and the Dirac fermion splits into pairs of Weyl fermions under the external magnetic effect. However, subsequent photoemission and STM experiments 39,40 clearly revealed that the robust electronic groundstate of ZrTe 5 is that of a gapped semiconductor with a small (∼ 50 meV) gap (not a Dirac semimetal). This suggests that a thorough theoretical understanding of the origins of the negative magneto-resistance in this material is lacking.…”

Section: Transport Response and The Chiral Anomalymentioning

confidence: 99%

Weyl semimetals, Fermi arcs and chiral anomalies

Jia¹,

Xu²,

Hasan³

2016

Nature Mater

314

255

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Physicists have discovered a novel topological semimetal, the Weyl semimetal, whose surface features a nonclosed Fermi surface while the low energy quasiparticles in the bulk emerge as Weyl fermions. Here they share a brief review of the development and present perspectives on the next step forward.Weyl semimetals are semimetals or metals whose quasiparticle excitation is the Weyl fermion, a particle that played a crucial role in quantum field theory but has not been observed as a fundamental particle in vacuum 1-24 . Weyl fermions have definite chiralities, either left-handed or right handed. In a Weyl semimetal, the chirality can be understood as a topologically protected chiral charge. Weyl nodes of opposite chirality are separated in momentum space and are connected only through the crystal boundary by an exotic nonclosed surface state, the Fermi arcs. Remarkably, Weyl fermions are robust while carrying currents, giving rise to exceptionally high mobilities. Their spins are locked to their momentum directions due to their character of momentum space magnetic monopole configuration.The presence of parallel electrical and magnetic fields can break the apparent conservation of the chiral charge due to the chiral anomaly, making a Weyl metal, unlike ordinary nonmagnetic metals, more conductive with an increasing magnetic field. These new topological phenomena beyond topological insulators make new physics accessible and suggest potential applications, despite the early stage of the research .In this Commentary, we will review key experimental progress and present an outlook for future directions of the field. Through this article, we hope to expound our perspectives on the key results and the experimental approaches currently used to access the novel physics as well as their limitations. Moreover, while most of the current experiments are still focusing on the discovery of new Weyl materials and demonstration of novel Weyl physics such as the chiral anomaly, it is becoming clear that a crucial step forward is to develop schemes for achieving quantum controls of the novel Weyl physics by electrical and optical means. We discuss some theoretical proposals along these lines highlighting the experimental techniques and matching materials conditions that are necessary for realizing these research directions. 2 MATERIAL SEARCHAlthough the theory of Weyl semimetal has been around for a long time in various forms 1-4 , its discovery had to wait until recent developments. This is because finding experimental realization requires appropriate materials simulation and characterizations. Historically, the first two material predictions, the pyrochlore iridates R 2 Ir 2 O 7 4 and the magnetically doped superlattice 6 , were both on time-reversal breaking (magnetic) materials.Perhaps influenced by the first works, for a long while, the community continued to focus on time-reversal breaking Weyl semimetals materials candidates 7,10 . These candidates were extensively studied by many experimental groups. Unfortunately, these ef...

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Evidence for Topological Edge States in a Large Energy Gap near the Step Edges on the Surface ofZrTe5

Cited by 168 publications

References 35 publications

Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior

Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior

Evidence for a Strong Topological Insulator Phase in ZrTe5

Weyl semimetals, Fermi arcs and chiral anomalies

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