Realization of insulating state and superconductivity in the Rashba semiconductor BiTeCl

Measurements of the resistivity, Hall coefficient, and Raman spectroscopy are performed on a Rashba semiconductor BiTeCl single crystal at high pressures up to 50 GPa. We find that applying pressure first induces a theoretically predicted insulating state, followed by a superconducting phase with an insulating normal state. Upon heavy compression, another different superconducting phase is entered into with a metallic normal state. A domelike evolution of the superconducting transition temperature with pressure is obtained with a crossover from the electron to hole carriers across the boundary of the two superconducting phases. These findings imply the possible realization of a topological state of the insulating and superconducting phases in this material.

Figure 1

Temperature dependence of the resistivity of BiTeCl at various pressures. (a) The sudden change in resistivity behavior indicates a phase transition from a Rashba semiconductor to an insulator at around 5 GPa. (b) The resistivity was gradually suppressed with increasing pressure and superconductivity emerges at above 13 GPa. The normal state behaves as an insulator (c) and a metal (d) upon heavy compression.

Figure 2

Temperature dependence of the resistivity of BiTeCl at a pressure of 50.8 GPa with applied magnetic fields. Inset: Upper critical field $H_{\mathrm{c}2}$ for pressures of 24.1 and 50.8 GPa, respectively. $T_c$ was determined from the 90% resistivity transition. The color area represents the calculated $H_{\mathrm{c}2}$ from the Werthamer-Helfand-Hohenberg equation.

Figure 3

Raman spectra of BiTeCl at various pressures up to 39.4 GPa. The vibrational modes in the initial Rashba semiconductor are marked by arrows. The different spectra above 5 GPa and the absence of Raman peaks above 39 GPa are consistent with the different normal-state behaviors of the two superconducting phases.

Figure 4

Phase diagram of BiTeCl at high pressures. The lower panel shows the pressure dependence of the resistivity and Hall coefficient measured at 10 K. The dashed regions represent the phase borders of a semiconductor (S), insulator (I), and metal (M). Two high-pressure superconducting phases with insulating and metallic normal states. The dashed area represents the coexistence of two phases.