Gate-tunable Phase Transitions in 1T-TaS$_2$

TL;DR

This study demonstrates how ionic gating can induce and control multiple phase transitions, including superconductivity, in 1T-TaS$_2$ by modulating charge density and dimensionality, revealing new states of matter.

Contribution

It introduces an ionic field-effect transistor that uses lithium ion intercalation to tune phase states in 1T-TaS$_2$, enabling exploration of extreme charge doping effects.

Findings

Charge-density-wave states are three-dimensional and collapse in 2D limit.

Ionic gating induces Mott-insulator to metal transition with 5 orders of magnitude resistance change.

Superconductivity emerges in a charge-density-wave state under ionic gating.

Abstract

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-TaS$_2$. The extreme charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS$_2$, and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density-wave states in 1T-TaS$_2$ 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-TaS$_2$ 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.