LAUSR

The superconductivity in the rare-earth transition-metal ternary borides RRuB2 (where R = Lu and Y) has been investigated using muon-spin rotation and relaxation. Measurements made in zero field suggest that time-reversal symmetry is preserved upon entering the superconducting state in both materials; a small difference in depolarization is observed above and below the superconducting transition in both compounds, however, this has been attributed to quasistatic magnetic fluctuations. Transverse-field measurements of the flux-line lattice indicate that the superconductivity in both materials is fully gapped, with a conventional s-wave pairing symmetry and BCS-like magnitudes for the zero-temperature gap energies. The electronic properties of the charge carriers in the superconducting state have been calculated, with effective masses m∗/me = 9.8 ± 0.1 and 15.0 ± 0.1 in the Lu and Y compounds, respectively, with superconducting carrier densities ns = (2.73 ± 0.04) × 10^28 m^(−3) and (2.17 ± 0.02) × 10^28 m^(−3). The materials have been classified according to the Uemura scheme for superconductivity, with values for Tc/TF of 1/(414 ± 6) and 1/(304 ± 3), implying that the superconductivity may not be entirely conventional in nature.