Enhanced superconductivity in spin–orbit proximitized bilayer graphene

Yiran Zhang, Robert Polski, Alex Thomson, Étienne Lantagne-Hurtubise, Cyprian Lewandowski, Haoxin Zhou, Kenji Watanabe, Takashi Taniguchi, Jason Alicea and Stevan Nadj-Perge ()
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Yiran Zhang: California Institute of Technology
Robert Polski: California Institute of Technology
Alex Thomson: California Institute of Technology
Étienne Lantagne-Hurtubise: California Institute of Technology
Cyprian Lewandowski: California Institute of Technology
Haoxin Zhou: California Institute of Technology
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Jason Alicea: California Institute of Technology
Stevan Nadj-Perge: California Institute of Technology

Nature, 2023, vol. 613, issue 7943, 268-273

Abstract: Abstract In the presence of a large perpendicular electric field, Bernal-stacked bilayer graphene (BLG) features several broken-symmetry metallic phases1–3 as well as magnetic-field-induced superconductivity1. The superconducting state is quite fragile, however, appearing only in a narrow window of density and with a maximum critical temperature Tc ≈ 30 mK. Here we show that placing monolayer tungsten diselenide (WSe2) on BLG promotes Cooper pairing to an extraordinary degree: superconductivity appears at zero magnetic field, exhibits an order of magnitude enhancement in Tc and occurs over a density range that is wider by a factor of eight. By mapping quantum oscillations in BLG–WSe2 as a function of electric field and doping, we establish that superconductivity emerges throughout a region for which the normal state is polarized, with two out of four spin-valley flavours predominantly populated. In-plane magnetic field measurements further reveal that superconductivity in BLG–WSe2 can exhibit 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 WSe2, indicating that proximity-induced (Ising) spin–orbit coupling plays a key role in stabilizing the pairing. Our results pave the way for engineering robust, highly tunable and ultra-clean graphene-based superconductors.

Date: 2023
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DOI: 10.1038/s41586-022-05446-x

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