Low-Temperature 2D/2D Ohmic Contacts in WSe$_2$ Field-Effect Transistors as a Platform for the 2D Metal-Insulator Transition

TL;DR

This paper presents the fabrication of high-quality WSe$_2$ devices with low-temperature Ohmic contacts, enabling detailed study of the 2D metal-insulator transition driven by electron interactions and disorder.

Contribution

It introduces a novel contact engineering approach for WSe$_2$ transistors that allows precise investigation of quantum phase transitions in 2D materials.

Findings

Ohmic contacts achieved down to 0.25 K

Scaling behavior consistent with a quantum phase transition

Disorder-induced local magnetic moments observed

Abstract

We report the fabrication of hexagonal-boron-nitride (hBN) encapsulated multi-terminal WSe$_2$ Hall bars with 2D/2D low-temperature Ohmic contacts as a platform for investigating the two-dimensional (2D) metal-insulator transition. We demonstrate that the WSe$_2$ devices exhibit Ohmic behavior down to 0.25 K and at low enough excitation voltages to avoid current-heating effects. Additionally, the high-quality hBN-encapsulated WSe$_2$ devices in ideal Hall-bar geometry enable us to accurately determine the carrier density. Measurements of the temperature ($T$) and density ($n_s$) dependence of the conductivity $\sigma(T,n_s)$ demonstrate scaling behavior consistent with a metal-insulator quantum phase transition driven by electron-electron interactions, but where disorder-induced local magnetic moments are also present. Our findings pave the way for further studies of the fundamental quantum mechanical properties of 2D transition metal dichalcogenides using the same contact engineering.