Two-dimensional ground-state mapping of a Mott-Hubbard system in a flexible field-effect device

TL;DR

This study presents a two-dimensional phase diagram of a Mott insulator using an organic field-effect device, revealing unexpected features and aiding understanding of the Mott-Hubbard model.

Contribution

It introduces a novel two-dimensional ground-state mapping technique controlling bandwidth and bandfilling simultaneously.

Findings

Observation of an abrupt first-order superconducting transition

Recurrent insulating phase in heavily electron-doped region

Nearly constant superconducting transition temperature across a wide parameter range

Abstract

A Mott insulator sometimes induces unconventional superconductivity in its neighbors when doped and/or pressurized. Because the phase diagram should be strongly related to the microscopic mechanism of the superconductivity, it is important to obtain the global phase diagram surrounding the Mott insulating state. However, the parameter available for controlling the ground state of most Mott insulating materials is one-dimensional owing to technical limitations. Here we present a two-dimensional ground-state mapping for a Mott insulator using an organic field-effect device by simultaneously tuning the bandwidth and bandfilling. The observed phase diagram showed many unexpected features such as an abrupt first-order superconducting transition under electron doping, a recurrent insulating phase in the heavily electron-doped region, and a nearly constant superconducting transition temperature in a wide parameter range. These results are expected to contribute toward elucidating one of the standard solutions for the Mott-Hubbard model. Theoretical calculations reproducing the main features of our experimental results have also been conducted.