  A pressure-induced topological quantum phase transition has been
theoretically predicted for the semiconductor BiTeI with giant Rashba spin
splitting. In this work, the evolution of the electrical transport properties
in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent
resistivity in a wide temperature range passes through a minimum at around 3
GPa, indicating the predicted transition in BiTeI. Superconductivity is
observed in both BiTeI and BiTeBr while the resistivity at higher temperatures
still exhibits semiconducting behavior. Theoretical calculations suggest that
the superconductivity may develop from the multi-valley semiconductor phase.
The superconducting transition temperature Tc increases with applied pressure
and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa
for BiTeBr), followed by a slow decrease. Our results demonstrate that BiTeX (X
= I, Br) compounds with non-trivial topology of electronic states display new
ground states upon compression.
