ZrTe5 is a newly discovered topological material. Shortly after a single layer ZrTe5 had been predicted to be a two-dimensional topological insulator, a handful of experiments have been carried out on bulk ZrTe5 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 ZrTe5 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.
@article{arxiv.1511.09315,
title = {Electrical transport in nano-thick ZrTe$_5$ sheets: from three to two dimensions},
author = {Jingjing Niu and Jingyue Wang and Zhijie He and Chenglong Zhang and Xinqi Li and Tuocheng Cai and Xiumei Ma and Shuang Jia and Dapeng Yu and Xiaosong Wu},
journal= {arXiv preprint arXiv:1511.09315},
year = {2017}
}