Superconductivity from repulsive interactions
The interaction between electrons in correlated quantum materials can give rise to new collective phases that cannot be understood based on single-particle properties. Superconductivity is one of the (many) fascinating examples. At its heart is the question about the glue that overcomes Coulomb repulsion and binds electrons into the pairs that form the superconducting condensate. In conventional superconductors, BCS theory gave us the answer in terms of electron-phonon interaction. However, many strongly-correlated quantum materials show evidence for an unconventional pairing mechanism that does not involve phonons. Examples include cuprates, iron-based superconductors or graphene heterostructures.
In this course, we will investigate if a repulsive Coulomb interaction can itself give rise to superconductivity. To this end, it is crucial to account for the renormalisation of the effective interaction in a theoretical description. We will see how this can induce a pairing instability and yield a superconducting state with new symmetry or topology. We will study its phenomenological treatment and discuss examples for potential electronic pairing mechanisms in recent quantum materials.