The symmetry of the superconducting order parameter in PuCoGa${}_5$

Abstract

The symmetry of the superconducting order parameter in single-crystalline PuCoGa${}_5$ ($T_{\mathrm{c}}=18.5$ K) is investigated via zero- and transverse- field muon spin relaxation ($\mu$SR) measurements, probing the possible existence of orbital and/or spin moments (time reversal-symmetry violation TRV) associated with the superconducting phase and the in-plane magnetic-field penetration depth $\lambda (T)$ in the mixed state, respectively. We find no evidence for TRV, and show that the superfluid density, or alternatively, $\Delta \lambda (T)=\lambda (T)-\lambda (0)$, are $\propto T$ for $T/T_{\mathrm{c}}\le 0.5$. Taken together these measurements are consistent with an even-parity (pseudo-spin singlet), d-wave pairing state.

4 pages, 5 figures