New results from experimental studies of single-crystal quantum structures of spin-triplet superconductor Sr$_{2}$RuO$_{4}$

Sr$_{2}$RuO$_{4}$, the only layered perovskite that becomes superconducting without the presence of Cu, was predicted to be an odd-parity, spin-triplet (possibly chiral p-wave) superconductor shortly after the discovery of its superconductivity. This prediction was supported by intensive work in the past two decades. Our experimental studies of Sr$_{2}$RuO$_{4}$ aim at detecting novel topological objects predicted for this superconducting material, including chiral edge currents, domains and domain walls, half-quantum vortices, and others. We established a process to prepare single-crystal quantum structures of Sr$_{2}$RuO$_{4}$ starting from mechanically exfoliated thin flakes. We identified Ru-free flakes of Sr$_{2}$RuO$_{4}$ showing enhanced superconductivity and demonstrated the link between the local enhancement of $T_{\mathrm{c}}$ and the presence of edge dislocations due to symmetry lowering. We fabricated mesoscopic superconducting rings of Sr$_{2}$RuO$_{4}$ and carried out Little-Parks resistance oscillation measurements, finding anomalously large resistance oscillations of full-flux period. With the application of an in-plane field and a large measurement current, the emergence of a second set of resistance oscillations was observed that suggested the existence of half-flux L-P resistance oscillations. Further experimental issues need to be clarified before the half-flux L-P resistance oscillations are fully established.