Abstract
The superconducting state of the caged type compound has been investigated by using magnetization, heat capacity, and muon spin relaxation or rotation measurements, and the results interpreted on the basis of the group theoretical classifications of the possible pairing symmetries and a simple model of the resulting quasiparticle spectra. Our zero-field measurements clearly reveal the spontaneous appearance of an internal magnetic field below the transition temperature, which indicates that the superconducting state in this material is characterized by broken time-reversal symmetry. Further, the analysis of the temperature dependence of the magnetic penetration depth measured using the transverse-field measurements suggests an isotropic character for the superconducting gap. This is in agreement with the heat capacity behavior, and we show that it can be interpreted in terms of a nonunitary triplet state with point nodes and an open Fermi surface.
- Received 10 September 2014
- Revised 19 January 2015
DOI:https://doi.org/10.1103/PhysRevB.91.060503
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