Electrical transport in nano-thick ZrTe$_5$ sheets: from three to two dimensions

TL;DR

This study investigates ultra-thin ZrTe$_5$ flakes, revealing thickness-dependent electronic properties, persistent metallic behavior at higher temperatures, and tunability via ionic gating, highlighting the impact of dimensional reduction on its topological characteristics.

Contribution

First transport measurements on nano-thick ZrTe$_5$ sheets demonstrate how thickness influences electronic behavior and band structure, advancing understanding of its topological properties.

Findings

Metallic behavior persists above 320 K in flakes thinner than 20 nm.

Resistivity maximum is highly tunable by ionic gating.

Band structure shifts with thickness, affecting topological states.

Abstract

ZrTe$_5$ is a newly discovered topological material. Shortly after a single layer ZrTe$_5$ had been predicted to be a two-dimensional topological insulator, a handful of experiments have been carried out on bulk ZrTe$_5$ crystals, which however suggest that its bulk form may be a three-dimensional topological Dirac semimetal. We report the first transport study on ultra thin ZrTe$_5$ flakes down to 10 nm. A significant modulation of the characteristic resistivity maximum in the temperature dependence by thickness has been observed. Remarkably, the metallic behavior, occurring only below about 150 K in bulk, persists to over 320 K for flakes less than 20 nm thick. Furthermore, the resistivity maximum can be greatly tuned by ionic gating. Combined with the Hall resistance, we identify contributions from a semiconducting and a semimetallic bands. The enhancement of the metallic state in thin flakes are consequence of shifting of the energy bands. Our results suggest that the band structure sensitively depends on the film thickness, which may explain the divergent experimental observations on bulk materials.