Interaction-driven topological insulator states in strained graphene

TL;DR

This paper demonstrates that Coulomb interactions in strained graphene with pseudo-magnetic fields induce topological insulator-like states, including quantum Hall and quantum spin-Hall states, stable at high temperatures due to many-body effects.

Contribution

It reveals how electron-electron interactions in strained graphene lead to topological insulator states, a novel mechanism for realizing such states in a material with engineered strain.

Findings

Interaction lifts degeneracies of pseudo Landau levels in strained graphene.

Spontaneous emergence of quantum Hall states at specific fillings.

Quantum spin-Hall states stabilized by spin-orbital interactions.

Abstract

The electronic properties of graphene can be manipulated via mechanical deformations, which opens prospects for studying the Dirac fermions in new regimes and for new device applications. Certain natural configurations of strain generate large nearly uniform pseudo-magnetic fields, which have opposite signs in the two valleys, and give rise to flat spin- and valley-degenerate pseudo Landau levels (PLLs). Here we consider the effect of the Coulomb interactions in strained graphene with uniform pseudo-magnetic field. We show that the spin/valley degeneracies of the PLLs get lifted by the interactions, giving rise to topological insulator-like states. In particular, when a nonzero PLL is quarter- or three-quarter filled, an anomalous quantum Hall state spontaneously breaking time-reversal symmetry emerges. At half-filled PLL, weak spin-orbital interaction stabilizes time-reversal-symmetric quantum spin-Hall state. These many-body states are characterized by the quantized conductance and persist to a high temperature scale set by the Coulomb interactions, which we estimate to be a few hundreds Kelvin at moderate strain values. At fractional fillings, fractional quantum Hall states breaking valley symmetry emerge. These results suggest a new route to realizing robust topological insulator states in mesoscopic graphene.