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Quenched metastable vortex states in Sr2RuO4

Sr2RuO4, a leading-candidate spin-triplet superconductor and a highly anisotropic quasi-two-dimensional type-II superconductor, provides 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 newly 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 by 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 liquid-like vortex state in the low-field region.