Suppression of the energy gap in SmB6under pressure

The electrical resistance $R$ of Sm${\mathrm{B}}_6$ as a function of temperature $T$ and pressure $P$ has been measured in the range $1 \mathrm{K}<~T<~300 \mathrm{K}$ and $0<~P\lesssim 220$ kbar. The behavior of $R\left(T\right)\mathrm{}$ changes continuously from that of a narrow gap semiconductor to that of a metal in the range of $0<~P\lesssim 70$ kbar. The dependence of $R$ on $T$ and $P$ can be analyzed phenomenologically within the context of a thermal activation model with an activation energy that decreases linearly with pressure from ∼33 K at zero pressure to zero at ∼70 kbar. The data resemble those of SmS and SmSe under pressure and suggest a general behavior of $R(T,P)\mathrm{}$ for intermediate-valence Sm compounds.