Fractional topological phases and broken time reversal symmetry in strained graphene

TL;DR

Strained graphene can host fractional topological quantum states without magnetic fields, with interactions leading to valley-polarized or symmetric exotic phases, including fractional quantum Hall liquids and topological insulators.

Contribution

This work demonstrates the potential of strained honeycomb lattices to realize fractional topological states and explores how interaction tuning can stabilize novel valley and spin phases.

Findings

Strain induces pseudo magnetic fields up to 300 Tesla.

Fractional quantum Hall states break time reversal symmetry.

Interaction engineering stabilizes valley symmetric topological phases.

Abstract

We show that strained or deformed honeycomb lattices are promising platforms to realize fractional topological quantum states in the absence of any magnetic field. The strained induced pseudo magnetic fields are oppositely oriented in the two valleys [1-3] and can be as large as 60-300 Tesla as reported in recent experiments [4,5]. For strained graphene at neutrality, a spin or a valley polarized state is predicted depending on the value of the onsite Coulomb interaction. At fractional filling, the unscreened Coulomb interaction leads to a valley polarized Fractional Quantum Hall liquid which spontaneously breaks time reversal symmetry. Motivated by artificial graphene systems [5-8], we consider tuning the short range part of interactions, and demonstrate that exotic valley symmetric states, including a valley Fractional Topological Insulator and a spin triplet superconductor, can be stabilized by such interaction engineering.