Strain induced superconducting pair-density-wave states in graphene

TL;DR

This paper demonstrates that strain-induced topological flat-bands in graphene can stabilize various unconventional superconducting states, including pair-density waves, coexisting with charge density waves, revealing new pathways to realize superconductivity in graphene.

Contribution

It introduces a mechanism for inducing and stabilizing chiral d-wave and pair-density-wave superconductivity in strained graphene via topological flat-bands.

Findings

Strain in graphene induces topological flat-bands facilitating superconductivity.

Chiral d-wave superconductivity coexists with charge and pair density waves.

A pure pair-density-wave state with finite superfluid density emerges at finite temperature.

Abstract

Graphene is known to be non-superconducting. However, surprising superconductivity is recently discovered in a flat-band in a twisted bi-layer graphene. Here we show that superconductivity can be more easily realized in topological flat-bands induced by strain in graphene through periodic ripples. Specifically, it is shown that by including correlation effects, the chiral d-wave superconductivity can be stabilized under strain even for slightly doped graphene. The chiral d-wave superconductivity generally coexists with charge density waves (CDW) and pair density waves (PDW) of the same period. Remarkably, a pure PDW state with doubled period that coexists with the CDW state is found to emerge at a finite temperature region under reasonable strain strength. The emergent PDW state is shown to be superconducting with non-vanishing superfluid density, and it realizes the long searched superconducting states with non-vanishing center of mass momentum for Cooper pairs.