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Physics Seminar

Complex superconducting order

Speaker: Dr Jorge Quintanilla (Kent University)
Date: Wednesday 13 February 2019
Time: 15:00
Venue: Queens Buildings N/3.28

Superconductivity is a macroscopic quantum phenomenon where the electrons in a metal behave coherently, like photons in a LASER. The essential feature of the superconducting state, compared to a normal metal, is that it is more ordered - in other words, some symmetries are broken. There is a consensus that all superconductors break global gauge symmetry, meaning that the phase of the wave function is locked to a fixed, randomly-chosen value. On the other hand many so-called "unconventional" superconductors break additional symmetries. Unfortunately it has been difficult, even after decades of research in some cases, to establish the nature of their ordered states. In this talk I will discuss the issue in the light of recent experimental discoveries. These have uncovered evidence of broken time-reversal symmetry (the same form of symmetry breaking occurring in magnets) in materials that were expected to be conventional superconductors. I will explain how we have been piecing together a theoretical understanding of these new materials. The picture that emerges is one of complexity: these systems have complicated band structures affording new degrees of freedom which have to be fully taken into account in order to describe their novel superconducting states, including inter-orbital equal-spin pairing and states with standing loop super-currents on the atomic scale. I will conclude by speculating on the possibility to engineer analogues of some of these states in quantum dot arrays made of conventional superconductors