PhD defense: Clara Neerup Breiø
Interaction- and Disorder-Induced Phases in Electronically Correlated Materials
Interactions between the microscopic constituents of many-body quantum systems are a fundamental challenge in condensed matter physics. The inconceivable complexity associated with the mutual attraction and repulsion among the myriad of particles necessitates formulations of effective models capturing a minuscule, yet determining, fraction of the dynamics. However, the intricacy of the microscopic interactions also leads to fascinating many-body quantum phases of matter. This defence will provide insight into effects arising from the presence of defects in microscopically ordered states. In particular, the response to defects, both in the form of multiple atomic impurities and dislocation-induced lattice relaxation, in unconventional superconductors will be investigated. The studies will assume an attractive nearest-neighbor superconducting pairing mechanism to be present and compute selfconsistent mean-field simulations of the bond-pairings on
the imperfection-modified lattice. The results provide evidence for a general notion of defect-induced spontaneous time-reversal symmetry breaking generated by local loop currents in an otherwise time-reversal symmetric superconductor. The notion questions the current interpretation of experimental evidence for time-reversal symmetry breaking as a global order in unconventional superconductors.
Additionally, a study on impurity-assisted detection of global symmetry-preserving anti-ferro-orbital order in an unconventional superconductor will be presented. Employing a T-matrix approach, theoretical computations will predict an interesting superconductivity-enhanced response in the quasiparticle interference anisotropy originating from the local orbital order and emerging in the vicinity of singleatom impurities. The predictions are corroborated by scanning tunneling microscopy measurements on Co-terminated CeCoIn5. The findings suggest that the method could be utilized to detect other, thus far, hidden orders in unconventional superconductors.