Spin-Orbit Enhanced Superconductivity in Bernal Bilayer Graphene

TL;DR

This study demonstrates that placing monolayer WSe₂ on Bernal bilayer graphene significantly enhances superconductivity, increasing critical temperature, broadening the density range, and enabling zero-field superconductivity through proximity-induced spin-orbit coupling.

Contribution

It reveals that WSe₂ induces strong spin-orbit coupling in bilayer graphene, leading to robust, tunable superconductivity at zero magnetic field with higher critical temperatures.

Findings

Superconductivity appears at zero magnetic field with increased Tc.

Superconductivity occurs over a wider density range.

Proximity-induced spin-orbit coupling enhances pairing.

Abstract

In the presence of a large perpendicular electric field, Bernal-stacked bilayer graphene (BLG) features several broken-symmetry metallic phases as well as magnetic-field-induced superconductivity. The superconducting state is quite fragile, however, appearing only in a narrow window of density and with a maximum critical temperature $T_c\approx30$~mK. Here, we show that placing monolayer tungsten diselenide (WSe$_{2}$) on BLG promotes Cooper pairing to an extraordinary degree: superconductivity appears at zero magnetic field, exhibits an order of magnitude enhancement in $T_c$, and occurs over a density range that is wider by a factor of eight. By mapping quantum oscillations in BLG-WSe$_2$ as a function of electric field and doping, we establish that superconductivity emerges throughout a region whose normal state is polarized, with two out of four spin-valley flavours predominantly populated. In-plane magnetic field measurements further reveal a striking dependence of the critical field on doping, with the Chandrasekhar-Clogston (Pauli) limit roughly obeyed on one end of the superconducting dome yet sharply violated on the other. Moreover, the superconductivity arises only for perpendicular electric fields that push BLG hole wavefunctions towards WSe$_2$ -- suggesting that proximity-induced (Ising) spin-orbit coupling plays a key role in enhancing the pairing. Our results pave the way for engineering robust, highly tunable, and ultra-clean graphene-based superconductors.