Researchers have discovered a new type of superconductivity in twisted bilayer graphene (TBG) with a twist angle of 1.08 degrees, characterized by a small Fermi surface. This finding is significant because the observed superconductivity exhibits properties consistent with a resonating-valence-bond (RVB) state, a concept originally proposed by Philip Anderson to explain superconductivity in high-temperature cuprates. The small Fermi surface in this system suggests that electrons behave in a way that favors the formation of Cooper pairs without phonon mediation, a mechanism distinct from conventional BCS theory.

The study focused on measuring the electronic transport properties and heat capacity of the TBG. The results indicate a superconducting phase with an energy gap that opens at low temperatures, and a temperature dependence of resistance that does not fit simple s-wave or d-wave superconductivity models. Evidence for a small Fermi surface was obtained through Shubnikov-de Haas oscillation measurements, which revealed a very low carrier density in the normal phase adjacent to superconductivity.

This work opens new avenues for understanding unconventional superconductivity. The identification of an RVB state in a two-dimensional graphene material provides a versatile platform for studying strong electron interactions and correlation physics. The ability to tune the electronic properties of TBG through the twist angle and applied electric fields offers unprecedented control to explore the underlying mechanisms of high-temperature superconductivity and potentially design new superconducting materials with enhanced properties.