Abstract
The superconducting state of the filled skutterudite alloy series has been systematically studied by specific heat and zero-field muon spin relaxation (), while the critical fields have been determined by magnetization measurements. An additional inhomogeneous local magnetic field, indicative of broken time-reversal symmetry, is observed in the superconducting states of the alloys. For , the broken-TRS phase sets in below a temperature , distinctly lower than the superconducting transition temperature . For . The local field strength decreases as , where is characterized by conventional pairing. The lower critical field of shows the onset of a second quadratic temperature region below . Upper critical field measurements suggest multiband superconductivity, and point gap nodes are consistent with the specific heat data. In , only a single specific-heat discontinuity is observed at , in contrast to the second jump seen in below . These results suggest that superconductivity in is characterized by a complex order parameter.
4 More- Received 31 January 2019
- Revised 20 June 2019
DOI:https://doi.org/10.1103/PhysRevB.100.024508
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