Pressure-induced superconductivity in the giant Rashba system BiTeI*

At ambient pressure, BiTeI is the first material found to exhibit a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to $\sim 40$~GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic $P4/nmm$ structure BiTeI is a metal. We find that this structure is superconducting with $T_c$ values as high as 6~K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute $T_c$ and find that our data is consistent with phonon-mediated superconductivity.