Excitonic insulator states in molecular functionalized atomically-thin semiconductors

TL;DR

This paper proposes a new class of two-dimensional hybrid materials functionalized with organic molecules as potential room-temperature excitonic insulators, providing theoretical phase diagrams and optical detection methods.

Contribution

It introduces a novel material system, WS$_2$-F6TCNNQ, as a candidate for room-temperature excitonic insulators with detailed phase diagrams and optical characterization strategies.

Findings

WS$_2$-F6TCNNQ exhibits an excitonic insulating phase at room temperature.

Phase diagrams are calculated for temperature, gap energy, and dielectric environment.

Optical methods for detecting excitonic phases are proposed.

Abstract

The excitonic insulator is an elusive electronic phase exhibiting a correlated excitonic ground state. Materials with such a phase are expected to have intriguing properties such as excitonic high-temperature superconductivity. However, compelling evidence on the experimental realization is still missing. Here, we theoretically propose hybrids of two-dimensional semiconductors functionalized by organic molecules as prototypes of excitonic insulators, with the exemplary candidate WS$_2$-F6TCNNQ. This material system exhibits an excitonic insulating phase at room temperature with a ground state formed by a condensate of interlayer excitons. To address an experimentally relevant situation, we calculate the corresponding phase diagram for the important parameters: temperature, gap energy, and dielectric environment. Further, to guide future experimental detection, we show how to optically characterize the different electronic phases via far-infrared to terahertz (THz) spectroscopy.