High-pressure effect on the superconductivity of YB6

Pressure effects on superconducting properties of two YB6 samples (T-c = 5.9 and 7.5 K) were investigated by measurements of electrical resistivity, magnetic susceptibility, and x-ray diffraction in the pressure range up to 320 kbar. Magnetoresistivity measurements down to 60 mK and up to 47 kbar have shown a negative pressure effect on T-c as well as on the third critical field H-c3 with the slopes dlnT(c)/dp = -0.59%/kbar and dlnH(c3)/dp = -1.1%/kbar, respectively. The magnetic susceptibility measurements evidenced that the slope of dlnT(c)/dp gradually decreases with pressure reaching a value three times smaller at 112 kbar. The lattice parameter measurements revealed the volume reduction of 14% at 320 kbar. The pressure-volume dependence is described by the Rose-Vinet equation of state. The obtained relative volume dependence dlnT(c)/dlnV analyzed by the McMillan formula for T-c indicates that the reduction of the superconducting transition temperature is mainly due to hardening of the Einstein-like phonon mode responsible for the superconducting coupling. This is confirmed by the analysis of the resistivity measurements in the normal state up to T = 300 K performed at pressures up to 28 kbar.