Pressure-induced superconductivity in $n$-type bismuth telluride

Stoichiometric bismuth telluride (Bi$_2$Te$_3$), which is a $p$-type semiconductor, has the rhombohedral structure with space group $R$-3$m$ at ambient condition. We have previously reported that pressure-induced superconductivity of stoichiometric $p$-type Bi$_2$Te$_3$ occurs in the high-pressure phases which appear above 8 GPa. However Bi$_2$Te$_3$ shows the variations of the carrier types, the carrier density, and the transport properties with the atomic composition. In this study, we performed the x-ray diffraction study and the electrical resistivity measurement of Bi$_{35}$Te$_{65}$ as the $n$-type Bi$_{2}$Te$_{3}$ sample under high pressure to investigate structural phase transition and pressure-induced superconductivity. At ambient condition, Bi$_{35}$Te$_{65}$ has also the $R$-3$m$ structure. It remains stable up to 8 GPa at room temperature. The superconducting transition is observed at 6 GPa below 2.9 K. The electrical resistivity at room temperature decreases rapidly at pressures from 7 to 8 GPa, indicating the occurrence of structural phase transition. It suggests that the superconducting transition at 6 GPa occurs at the ambient pressure phase with the $R$-3$m$ structure.