Project title: Interplay between symmetry-breaking distortions and superconductivity in layered cuprates.
Supervisors: Arash Mostofi (Imperial College), Nicholas Bristowe (University of Kent) and Mark Senn (University of Warwick)
The discovery of high-temperature superconductivity (HTS) in the La2-xBaxCuO4 Ruddlesden-Popper (RP) system in 1986 has stimulated a tremendous amount of research in understanding the origin of this unconventional superconductivity. The underlying mechanisms leading to such phenomena in the cuprates cannot be explained by BardeenCooper-Schrieffer (BCS) theory, which argues that conventional superconductivity arises due to small attractive interactions between electrons, causing them to form Cooper pairs and condense. Despite intensive research efforts in understanding the wealth of unusual properties these cuprates exhibit, there currently exists no microscopic theory which can account for all of their properties. It has been proposed that superconductivity arises due to electron-phonon coupling mediated by Jahn-Teller polarons, but the exact nature of these quasiparticles and their coupling to the lattice remains elusive.
Superconductivity in the RP cuprates only seems to arise in a single space group of orthorhombic symmetry and vanishes upon a structural phase transition to a tetragonal phase at low temperatures. In this project, we use theory and simulation based on firstprinciples calculations to investigate the phase transition from orthorhombic to tetragonal at low temperatures. This should help gain better insight into the nature of the lattice coupling giving rise to superconductivity in the orthorhombic system.