We studied the specific heat and thermal conductivity of the spin-triplet superconductor Sr2RuO4 at low temperatures and under oriented magnetic fields H. We resolved a double peak structure of the superconducting transition under magnetic field for the first time, which provides thermodynamic evidence for the existence of multiple superconducting phases. We also found a clear limiting of the upper critical field Hc2 for the field direction parallel to the RuO2 plane only within 2 degrees. The limiting of Hc2 occurs in the same H-T domain of the second superconducting phase; we suggest that the two phenomena have the same physical origin.
@article{arxiv.cond-mat/0210537,
title = {Superconducting Double Transition and the Upper Critical Field Limit of Sr2RuO4 in Parallel Magnetic Fields},
author = {Kazuhiko Deguchi and Makariy Tanatar and Zhiqiang Mao and Takehiko Ishiguro and Yoshiteru Maeno},
journal= {arXiv preprint arXiv:cond-mat/0210537},
year = {2009}
}