Observation of quasi-two-dimensional Dirac fermions in ZrTe5

Abstract

Since the discovery of graphene, layered materials have attracted extensive interest owing to their unique electronic and optical characteristics. Among them, Dirac semimetals, one of the most appealing categories, have been a long-sought objective in layered systems beyond graphene. Recently, layered pentatelluride ZrTe 5 was found to host signatures of a Dirac semimetal. However, the low Fermi level in ZrTe 5 strongly hinders a comprehensive understanding of the whole picture of electronic states through photoemission measurements, especially in the conduction band. Here, we report the observation of Dirac fermions in ZrTe 5 through magneto-optics and magneto-transport. By applying a magnetic field, we observe a ffiffiffiffi B p dependence of the inter-Landau-level resonance and Shubnikov-de Haas (SdH) oscillations with a nontrivial Berry phase, both of which are hallmarks of Dirac fermions. The angle-dependent SdH oscillations show a clear quasi-two-dimensional feature with a highly anisotropic Fermi surface and band topology, in stark contrast to the three-dimensional (3D) Dirac semimetal such as Cd 3 As 2 . This is further confirmed by the angle-dependent Berry phase measurements and the observation of bulk quantum Hall effect (QHE) plateaus. The unique band dispersion is theoretically understood: the system is at the critical point between a 3D Dirac semimetal and a topological insulator phase. With the confined interlayer dispersion and reducible dimensionality, our work establishes ZrTe 5 as an ideal platform for exploring the exotic physical phenomena of Dirac fermions. NPG Asia Materials (2016) 8, e325; doi:10.1038/am.2016.166; published online 11 November 2016 INTRODUCTION Layered materials, formed by stacking strongly bonded layers with weak interlayer coupling, 1-10 have drawn immense attention in fundamental studies and device applications owing to their tunability in band structures and Fermi energy. 3,4,[11][12][13] Unlike other layered materials such as MoS 2 and BN, graphene stands out as an appealing candidate, as it is featured with a linear energy dispersion and low-energy relativistic quasi-particles. 9,14,15 Many exotic phenomena, such as a half-integer quantum Hall effect (QHE) 1,2 and Klein tunneling, 16 have been realized in graphene. Along this line, extensive efforts were also devoted to exploring new Dirac semimetal states in other layered systems beyond graphene. 5,6 Pentatelluride ZrTe 5 with a layered orthorhombic structure has been widely studied since the 1980s for its resistivity anomaly [17][18][19] and large thermopower. 20,21 For a long time, ZrTe 5 was considered to be a semimetal or degenerated semiconductor with a parabolic energy dispersion. 10,22 However, a recent study 7 revealed a linear dispersion in ZrTe 5 bulk states along with a chiral magnetic effect, hosting the signatures of a Dirac semimetal. Nevertheless, owing to the relatively

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

“…The current was applied along the a axis, and the magnetic field was oriented along the b axis. Pronounced Shubnikov-de Haas (SdH) quantum oscillations are observed in MR at T ≤ 10 K, and the MR reaches about 900% at 1.8 K and 5 T, in agreement with the previous reports [14,30]. With increasing temperature, the SdH quantum oscillations smear out, and the magnitude of MR first decreases in the temperature range 1.8-100 K and then increases again up to 170 K as shown in Fig.…”

Thermodynamic signature of Dirac electrons across a possible topological transition in ZrTe5

“…Hall effect data shows electron-like carriers at low temperature [16], implying some of these additional bands must be populated and Dirac-like or massive Dirac-like features should be present. Note that these features are extremely sensitive to cell volume and strain [17], which may explain the conflicting experimental reports on the electronic properties and topological signatures in ZrTe 5 [4][5][6][7][8][9][10][11][12][13][14].…”

“…In this study we focus on ZrTe 5 , a material whose topological nature is hotly debated; it has been predicted and verified as a Dirac semimetal [4][5][6][7][8], a topological insulator [9][10][11][12] and a trivial semiconductor [13,14]. In addition to its potential topological nature, there is also an unusual anomaly in the temperature dependence of the resistivity that has been conjectured to originate from a Lifshitz transition [15,16].…”

Disruption of the Accidental Dirac Semimetal State in ZrTe5 under Hydrostatic Pressure

“…According to previous studies [21,22], at such tilted angle, the MR and S-dH quantum oscillations can still capture the electron behavior in the ab plane even if the field is not strictly alone the c-axis. At ambient pressure, ZrTe 5 exhibits large anisotropic magnetoresistance, i.e., the MR H c is only around 250% at 14 T, one order smaller than the MR H b .…”

“…1 represents temperature dependence of the normalized resistivity for ZrTe 5 single crystal at various pressures. At ambient pressure, the resistivity shows a broad peak at T * =132 K, which is known as the hallmark of ZrTe 5 [14,20,21]. Recent ARPES studies found out that the resistivity peak results from a temperature-induced Lifshitz-transition where ZrTe 5 evolves from semiconductor to n-type semimetal [29].…”