Quenched metastable vortex states in Sr₂RuO₄

Sr₂RuO₄, a leading-candidate spin-triplet superconductor and a highly anisotropic quasi-two-dimensional type II superconductor, provides a unique opportunity to study unconventional as well as conventional vortex phases. To investigate its vortex-matter phases, we studied the ac susceptibility of Sr₂RuO₄ for fields parallel to the RuO₂ plane by adapting two different thermal processes: In addition to the ordinary field sweep (FS) process, we employed the "each-point field-cooling" (EPFC) process, in which the superconductivity is once thermally destroyed before collecting the data. We find that the ac susceptibility signal substantially changes with the EPFC process. This result indicates that we succeed in inducing new metastable vortex states via the EPFC process. We also find a new field scale H∗1, below which the FS and EPFC processes provide the same value of the ac susceptibility. This new field scale suggests a liquidlike vortex state in the low-field region.