Two-Dimensional Quantum Hall Effect and Zero Energy State in Few-Layer ZrTe₅

Abstract

Topological matter plays a central role in today’s condensed matter research. Zirconium pentatelluride (ZrTe 5 ) has attracted attention as a Dirac semimetal at the boundary of weak and strong topological insulators (TI). Few-layer ZrTe 5 is anticipated to exhibit the quantum spin Hall effect due to topological states inside the band gap, but sample degradation inflicted by ambient conditions and processing has so far hampered the fabrication of high quality devices. The quantum Hall effect (QHE), serving as the litmus test for 2D systems to be considered of high quality, has not been observed so far. Only a 3D variant on bulk was reported. Here, we succeeded in preserving the intrinsic properties of thin films lifting the carrier mobility to ∼3500 cm 2 V –1 s –1 , sufficient to observe the integer QHE and a bulk band gap related zero-energy state. The magneto-transport results offer evidence for the gapless topological states within this gap.

The Anomalous Photo‐Nernst Effect of Massive Dirac Fermions In HfTe5

“…HfTe 5 and ZrTe 5 share an orthorhombic crystal structure, and their electronic structure lies at the border between a strong and weak topological insulator. [12][13][14][15][16][17] Being van der Waals materials, they can be exfoliated into two-dimensional (2D) systems, [18] with predictions of a quantum spin Hall phase in monolayers. [12] Yet, the exact bulk electronic structure remains under debate due to fact that small changes of the lattice parameters, e.g., due to strain, strongly modify the fundamental gap or induce secondary carrier pockets.…”

Gate-Tunable Multiband Transport in ZrTe5 Thin Devices

“…The exposure to air or solvents are fully avoided during the device fabrication process, which helps maintain the intrinsic properties of the ZrTe5 crystals. We also encapsulate the ZrTe5 on both sides with hexagonal boron nitrides (hBN), which further improve the sample quality and prevent sample degradation during loading into the cryostats 31 .…”

“…We also encapsulate the ZrTe 5 on both sides with hexagonal boron nitrides (hBN), which further improve the sample quality and prevent sample degradation during loading into the cryostats. 31 In this study, electrical transport measurements with changing gate voltages, temperatures, and magnetic fields are performed. Unless otherwise specified, the data presented below are collected from one representative device (about 12 nm thick, with an optical image being shown in Figure 1b).…”