The ability to tune material properties using gate electric field is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as gate-electric-field induced superconductivity and metal-insulator transition. Here we describe an ionic field-effect transistor (termed "iFET"), which uses gate-controlled lithium ion intercalation to modulate the material property of layered atomic crystal 1T-TaS2. The extreme charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2, and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density-wave states in 1T-TaS2 are three-dimensional in nature, and completely collapse in the two-dimensional limit defined by their critical thicknesses. Meanwhile the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes at low temperatures, with 5 orders of magnitude modulation in their resistance. Superconductivity emerges in a textured charge-density-wave state induced by ionic gating. Our method of gate-controlled intercalation of 2D atomic crystals in the bulk limit opens up new possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.
@article{arxiv.1407.3480,
title = {Gate-tunable Phase Transitions in 1T-TaS$_2$},
author = {Yijun Yu and Fangyuan Yang and Xiu Fang Lu and Ya Jun Yan and Y. H. Cho and Liguo Ma and Xiaohai Niu and Sejoong Kim and Young-Woo Son and Donglai Feng and Shiyan Li and Sang-Wook Cheong and Xian Hui Chen and Yuanbo Zhang},
journal= {arXiv preprint arXiv:1407.3480},
year = {2015}
}