Pressure effect on heavy fermion compound YbCu5

We report the first study of pressure effect on heavy fermion compound YbCu5. The nuclear magnetic resonance (NMR) and resistivity measurements under pressure indicate that electronic properties of YbCu5 gradually approach the localized-nonlocalized boundary with pressure. The critical pressure P c is estimated to be about 4GPa. Such pressure dependence contrasts with that of YbInCu 4 which shows the first-order transition from valence fluctuating to magnetically ordered states at P C = 2.4 GPa.