Electronic phase transition and partially gapped Fermi surface in superconducting Lu5Ir4Si/sub 10/

The enhancement of the superconducting transition temperature of Lu5Ir4Si/sub 10/ from 3.8 to 9.10K under pressure is caused by the suppression of an electronic phase transition which results in the partial gapping of the Fermi surface. Using electrical resistivity at ambient and high pressure, bulk-modulus, heat-capacity, upper-critical-magnetic-field, and static-magnetic-susceptibility measurements, we estimate that the density of electronic states at the Fermi level is reduced by 36% due to this phase transition. The transition, which occurs at 790K at ambient pressure, has the experimental characteristics indicative of charge- or spin-density-wave formation