Superconducting materials, like magic-angle graphene, allow electron pairs to bypass regular traffic and move through the material with zero friction. However, the ease with which these electron pairs can flow depends on several conditions, including density.
Physicists at MIT and Harvard University have directly measured superfluid stiffness for the first time in magic-angle graphene. This measurement will help scientists understand how the material superconducts and identify the mechanism of superconductivity.
The team’s measurements suggest that magic-angle graphene’s superconductivity is primarily governed by quantum geometry, which refers to the conceptual “shape” of quantum states that can exist in a given material. The results show a tenfold increase in superfluid stiffness compared to conventional expectations, with a temperature dependence consistent with what the theory of quantum geometry predicts.
To measure superfluid stiffness in magic-angle graphene, the team developed a new experimental method using a microwave resonator. They connected the graphene structure to the resonator and sent a microwave signal through it, measuring the resulting shift in its resonance frequency. This allowed them to infer the kinetic inductance of the graphene and convert it into a value of superfluid stiffness.
The researchers found that their approach was successful despite the challenge of working with atomically thin materials, which are typically 10 to 100 times thicker and larger in area than conventional samples. The team’s techniques for precisely connecting delicate materials will help build new types of quantum bits for future quantum-computing devices.
This research was funded by several organizations, including the U.S. Army Research Office, the National Science Foundation, and the U.S. Air Force Office of Scientific Research. A complementary study on magic-angle twisted trilayer graphene is also published in the same issue of Nature.
Source: https://news.mit.edu/2025/physicists-measure-key-aspect-superconductivity-magic-angle-graphene-0205