Spin-Triplet Excitonic Insulator: The Case of Graphone

TL;DR

This paper predicts the existence of a spin-triplet excitonic insulator in graphone, with a critical temperature of 11.5 K, and discusses its potential experimental detection through transport measurements and band transition observations.

Contribution

It introduces the possibility of spin-triplet excitonic insulators in two-dimensional systems like graphone, supported by first-principles calculations and an effective Hamiltonian.

Findings

Critical temperature of 11.5 K for the excitonic insulator.

Potential for detecting spin superfluidity via transport experiments.

Observation of an indirect-to-direct transition crossover in exciton dispersion.

Abstract

While various excitonic insulators have been studied in the literature, due to the perceived too-small spin splitting, spin-triplet excitonic insulator is rare. In two-dimensional systems such as a graphone, however, it is possible, as revealed by first-principles calculations coupled with Bethe-Salpeter equation. The critical temperature, given by an effective Hamiltonian, is 11.5 K. While detecting excitonic insulators is still a daunting challenge, the condensation of triplet excitons will result in spin superfluidity, which can be directly measured by a transport experiment. Nonlocal dielectric screening also leads to an unexpected phenomenon, namely, an indirect-to-direct transition crossover between single-particle band and exciton dispersion in graphone, which offers yet another test by experiment.