Superfluid stiffness of magic-angle twisted bilayer graphene

Miuko Tanaka, Joel Î-j. Wang (), Thao H. Dinh, Daniel Rodan-Legrain, Sameia Zaman, Max Hays, Aziza Almanakly, Bharath Kannan, David K. Kim, Bethany M. Niedzielski, Kyle Serniak, Mollie E. Schwartz, Kenji Watanabe, Takashi Taniguchi, Terry P. Orlando, Simon Gustavsson, Jeffrey A. Grover, Pablo Jarillo-Herrero () and William D. Oliver ()
Additional contact information
Miuko Tanaka: Massachusetts Institute of Technology
Joel Î-j. Wang: Massachusetts Institute of Technology
Thao H. Dinh: Massachusetts Institute of Technology
Daniel Rodan-Legrain: Massachusetts Institute of Technology
Sameia Zaman: Massachusetts Institute of Technology
Max Hays: Massachusetts Institute of Technology
Aziza Almanakly: Massachusetts Institute of Technology
Bharath Kannan: Massachusetts Institute of Technology
David K. Kim: Massachusetts Institute of Technology
Bethany M. Niedzielski: Massachusetts Institute of Technology
Kyle Serniak: Massachusetts Institute of Technology
Mollie E. Schwartz: Massachusetts Institute of Technology
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Terry P. Orlando: Massachusetts Institute of Technology
Simon Gustavsson: Massachusetts Institute of Technology
Jeffrey A. Grover: Massachusetts Institute of Technology
Pablo Jarillo-Herrero: Massachusetts Institute of Technology
William D. Oliver: Massachusetts Institute of Technology

Nature, 2025, vol. 638, issue 8049, 99-105

Abstract: Abstract The physics of superconductivity in magic-angle twisted bilayer graphene (MATBG) is a topic of keen interest in moiré systems research, and it may provide an insight into the pairing mechanism of other strongly correlated materials such as high-critical-temperature superconductors. Here we use d.c. transport and microwave circuit quantum electrodynamics to directly measure the superfluid stiffness of superconducting MATBG through its kinetic inductance. We find the superfluid stiffness to be much larger than expected from conventional Fermi liquid theory. Rather, it is comparable to theoretical predictions1 and recent experimental indications2 of quantum geometric effects that are dominant at the magic angle. The temperature dependence of the superfluid stiffness follows a power law, which contraindicates an isotropic Bardeen–Cooper–Schrieffer (BCS) model. Instead, the extracted power-law exponents indicate an anisotropic superconducting gap, whether interpreted in the Fermi liquid framework or by considering the quantum geometry of flat-band superconductivity. Moreover, a quadratic dependence of the superfluid stiffness on both d.c. and microwave current is observed, which is consistent with the Ginzburg–Landau theory. Taken together, our findings show that MATBG is an unconventional superconductor with an anisotropic gap and strongly suggest a connection between quantum geometry, superfluid stiffness and unconventional superconductivity in MATBG. The combined d.c.–microwave measurement platform used here is applicable to the investigation of other atomically thin superconductors.

Date: 2025
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DOI: 10.1038/s41586-024-08494-7

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