It is a long-standing prediction that correlated electron-hole states can occur in semiconductors with very small band gap or semimetals with very small band overlap, when cooled to a sufficiently low temperature, yielding a non-conducting Bose condensate. Such electron-hole paring degenerated quantum insulators are endowed with enriched intrinsic physics with Hamiltonians closely resembling that in superconductivity, and have attracted continuous attention since decades. However, owing to the dielectric screening and the recombination of electrons and holes, excitonic insulators remained largely unexplored in solids, especially in transport measurements.

In this talk, we will introduce our recent progresses in the experimental evidences of an exotic insulator: by bringing Bernal-stacked bilayer graphene into contact with a few-layered antiferromagnetic insulator CrOCl, the resulted vertical heterostructures can give rise to an extraordinarily robust ground state of insulator at the charge neutral [1]. The consequential over 1 GOhms insulator can be readily killed by tuning the vertical electrical field, in-plane electrical field, and effective doping, and the system recovers to a high mobility graphene with a sheet resistance of a few hundred Ohms. I-V curves as well as temperature- and magnetic field-dependences of conductance point such insulator to an excitonic insulating phase, which is attributed to the subtle coupling of graphene-CrOCl interface and the e-e interaction in the bilayer graphene [2-3]. Such interfacial coupling can therefore be a simple yet very powerful technique in effectively engineering the quantum electronic states.
 

[1] arXiv:2110.02921.
[2] arXiv:2206.05659.
[3] arXiv:2302.07543.
 

Zheng Vitto Han is a research professor at the Institute of Optoelectronics, Shanxi University. He got his PhD at Néel Institute in 2013 and did a post-Doc in Columbia University before he started his research group in 2015 in China. His studies mainly focus on the emerging physical properties of functional materials in mesoscopic sizes, and on further implementing these interesting properties in future applications of nano-assemblies and nanoelectronics. In the past few years, he has revealed a series of exotic physical properties of such systems, with the related works published in journals including Science, Nature Nanotechnology, Nature Communications.