Nodeless superconductivity and the peak effect in the quasiskutterudites Lu_3Os_4Ge_(13) and Y_3Ru_4Ge_(13)

摘要

We report an investigation of the superconducting states of Lu_3Os_4Ge_(13) and Y_3Ru_4Ge_(13) single crystals by measurements of the electrical resistivity, ac susceptibility, and London penetration depth. The analysis of the penetration depth and the derived superfluid density indicates the presence of nodeless superconductivity and suggests that there are multiple superconducting gaps in both materials. Furthermore, ac susceptibility measurements of both compounds display the peak effect in the low-temperature region of the H-T phase diagram. This anomalous increase of the critical current with field gives an indication of a change of the arrangement of flux lines in the mixed state, as found in some of the isostructural stannide materials.