Influence of Superconducting Order Parameter on Quasi-Particle Interference

Sammanfattning: Superconductors are important to study due to their many applications. Superconductivityarises when electron pairs, so-called Cooper pairs, form in the material.To understand the mechanism behind the formation of the Cooper pairs, the pairingsymmetry, described by the order parameter, must be found. One method to experimentallydetermine the order parameter is through quasi-particle interference.Quasi-particle interference (QPI) is a real space perturbation due to a defect andcan be experimentally imaged using scanning tunneling microscopy (STM), wherean atomic sized tip is scanned over a surface at a bias measuring the tunneling currentthrough the sample surface. QPI can also be theoretically calculated using atight-binding model describing the electronic structure and then using an interpolationbetween unit cells using wave functions to carry intra-unit cellular information,so-called Continuum QPI (CQPI). This report studies the influence of different superconductingorder parameters in a one-band cuprate-like material on theoreticallycalculated phase-referenced Fourier transformed CQPI (PRFT-CQPI). The resultsshow that this method gives qualitatively distinct results depending on the ordersymmetry, suggesting that it can be used to experimentally determine the superconductinggap symmetry. The results are also compared with experiment and withpreviously published CQPI calculations.