High-pressure effect on the superconductivity of YB6
Pressure effects on superconducting properties of two YB6 samples (Tc = 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 Tc as well as on the third critical field Hc3 with the slopes dlnTc/dp = -0.59%/kbar and dlnHc3/dp = -1.1%/kbar, respectively (Fig. 1). The magnetic susceptibility measurements evidenced that the slope of dlnTc/dp gradually decreases with pressure reaching a value three times smaller at 112 kbar (Fig. 2). The lattice parameter measurements revealed the volume, V, reduction of 14% at 320 kbar (Fig. 3). The obtained relative volume dependence lnTc vs lnV analyzed by the McMillan formula for Tc 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 with the “thermal spectroscopy” by the analysis of the resistivity in the normal state at various pressures (Fig. 4 and Fig. 5).