Unusual superconductivity could emerge in valley-imbalanced rhombohedral graphene

A groundbreaking study has revealed that an unusual form of graphene, called valley-imbalanced rhombohedral tetralayer graphene, may exhibit unconventional superconductivity. This type of superconductivity occurs at higher temperatures than typical superconductors and could potentially revolutionize the field of real-world superconducting devices.

The researchers at Harvard University and the University of Stuttgart demonstrated that this modified graphene could host superconducting states simultaneously at multiple incommensurate momenta, leading to the spontaneous formation of a superlattice of Cooper pairs. The study's authors were inspired by an experiment that showed superconductivity can emerge from a normal state in a specific stack of graphene layers, where electrons in two valleys of graphene spontaneously fill one valley over the other.

This imbalance in valley occupancy breaks the time-reversal symmetry, which is usually assumed to be absent in superconductivity theory. The researchers developed a theoretical framework to classify possible superconducting pairing instabilities in this unique material. Their work suggests that the superconductor could carry a special type of topology determined by the underlying interactions and may even spontaneously break translational symmetry.

Additionally, they found that superconductors emerging from valley-imbalanced normal states can spontaneously develop a vortex lattice, even without an external magnetic field. These findings open up new avenues for research into the unique properties and potential applications of superconductivity in valley-imbalanced rhombohedral graphene.