Spin-Triplet Excitonic Insulator: The Case of Semihydrogenated Graphene

Zeyu Jiang, Wenkai Lou, Yu Liu, Yuanchang Li, Haifeng Song, Kai Chang, Wenhui Duan, and Shengbai Zhang

Phys. Rev. Lett. 124, 166401 – Published 22 April 2020

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 semihydrogenated graphene (known as 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 the semihydrogenated graphene, which offers yet another test by experiment.

Received 10 November 2019
Accepted 30 March 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.166401

Physics Subject Headings (PhySH)

Excitons

Graphene

First-principles calculations

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Zeyu Jiang¹, Wenkai Lou ², Yu Liu ³, Yuanchang Li ^4,*, Haifeng Song ^3,5, Kai Chang^2,6, Wenhui Duan ^1,7, and Shengbai Zhang⁸

¹State Key Laboratory of Low-Dimensional Quantum Physics and Collaborative Innovation Center of Quantum Matter, Department of Physics, Tsinghua University, Beijing 100084, China
²SKLSM, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China
³Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
⁴Key Lab of advanced optoelectronic quantum architecture and measurement (MOE), and Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology, Beijing 100081, China
⁵CAEP Software Center for High Performance Numerical Simulation, Beijing 100088, China
⁶Beijing Academy of Quantum Information Sciences, Beijing 100193, China
⁷Institute for Advanced Study, Tsinghua University, Beijing 100084, China
⁸Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA