Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of strained graphene

TL;DR

This paper investigates how strain-induced flat bands in graphene enhance superconducting transition temperatures and explores the relationship between superfluid weight, BKT transition temperature, and doping, revealing potential pathways for higher-temperature superconductivity.

Contribution

The study provides new insights into the effects of strain on flat-band superconductivity and the BKT transition in graphene, including the impact of pair density waves and doping.

Findings

Strain-induced flat bands increase superconducting transition temperature by about 50%.

Superfluid weight for pair-density-wave states is lower than the gap-opening temperature.

BKT transition temperature versus doping exhibits a dome shape and depends linearly on spin-spin interaction.

Abstract

We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for highly unconventional superconducting states with the coexistence of chiral d-wave superconductivity, charge density waves and pair density waves in the strained graphene. Our results show that the strain-induced flat bands can promote the superconducting transition temperature approximately $50\%$ compared to that of the original doped graphene, which suggests that the flat-band superconductivity is a potential route to get superconductivity with higher critical temperatures. In particular, we obtain the superfluid weight for the pure superconducting pair-density-wave states from which the deduced superconducting transition temperature is shown to be much lower than the gap-opening temperature of the pair density wave, which is helpful to understand the phenomenon of the pseudogap state in high-$T_c$ cuprate superconductors. Finally, we show that the BKT transition temperature versus doping for strained graphene exhibits a dome-like shape and it depends linearly on the spin-spin interaction strength.