Physicists measure a key aspect of superconductivity in 'magic-angle' graphene showing it to be an unconventional superconductor

Amazing stuff!

Why is so much money wasted on windmills and solar panels instead of superconductivity research?

"... Physicists at MIT and Harvard University have now directly measured superfluid stiffness for the first time in "magic-angle" [bilayer] graphene—materials that are made from two or more atomically thin sheets of graphene twisted with respect to each other at just the right angle to enable a host of exceptional properties, including unconventional superconductivity. ...

Since its discovery in 2004, graphene ... In 2018, ... discovered that when two graphene sheets are stacked on top of each other, at a precise, "magic" angle, the twisted structure—known as magic-angle twisted bilayer graphene, or MATBG ..."

From the 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 predictions and recent experimental indications 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."

Physicists measure a key aspect of superconductivity in 'magic-angle' graphene

Physicists measure a key aspect of superconductivity in “magic-angle” graphene (original news release) "By determining how readily electron pairs flow through this material, scientists have taken a big step toward understanding its remarkable properties."

Superfluid stiffness of magic-angle twisted bilayer graphene (no public access)