# Multicomponent electron-hole superfluidity and the BCS-BEC crossover in double bilayer graphene

## TL;DR

This paper predicts multicomponent superfluidity in double bilayer graphene, exploring how tunable parameters like carrier density and band gap influence the BCS-BEC crossover and potential high-temperature superfluidity.

## Contribution

It introduces the concept of multicomponent superfluidity in bilayer graphene and analyzes how band gap and density tuning affect the BCS-BEC crossover.

## Key findings

- Small band gaps boost superfluid gaps but can weaken superfluidity.
- A band gap of 40-60 meV can induce strong-pairing BCS-BEC crossover.
- Optimal conditions for high-$T_c$ superfluidity are identified.

## Abstract

Superfluidity in coupled electron-hole sheets of bilayer graphene is predicted here to be multicomponent because of the conduction and valence bands. We investigate the superfluid crossover properties as functions of the tunable carrier densities and the tunable energy band gap $E_g$. For small band gaps there is a significant boost in the two superfluid gaps, but the interaction driven excitations from the valence to the conduction band can weaken the superfluidity, even blocking the system from entering the BEC regime at low densities. At a given larger density, a band gap $E_g\sim 40$-$60$ meV can carry the system into the strong-pairing multiband BCS-BEC crossover regime, the optimal range for realization of high-$T_c$ superfluidity.