Magnetoresistance oscillation study of the spin counterflow half-quantum vortex in doubly connected mesoscopic superconducting cylinders of Sr2RuO4

Vortices in an unconventional superconductor are an important subject for the fundamental study of superconductivity. A spin counterflow half-quantum vortex (HQV) was predicted theoretically for odd-parity, spin-triplet superconductors. Cantilever torque magnetometry measurements revealed previously experimental evidence for HQVs in doubly connected, single-crystal samples of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ with a mesoscopic size. However, important questions on the HQV, such as its stability, have remained largely unexplored. We report in this paper the detection of distinct features in vortex crossing induced magnetoresistance (MR) oscillations in doubly connected, mesoscopic cylinders of single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, which include a dip and secondary peak in MR, in the presence of a sufficiently large in-plane magnetic field. We argue that these features are due to the formation of spin counterflow HQV in a spin-triplet superconductor, which provides additional evidence for the existence of HQV and insights into the physics of this highly unusual topological object.