Pressure-induced superconductivity in non-stoichiometric bismuth telluride Bi$_{35}$Te$_{65}$

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. The transport properties of Bi$_2$Te$_3$, however, depend on the atomic composition; the dominant charge carriers change from hole to electron above 63at.\% Te. In this study, we performed the electrical resistivity measurement and the x-ray diffraction study of non-stoichiometric $n$-type Bi$_{35}$Te$_{65}$ under high pressure to investigate pressure-induced superconductivity and structural phase transition. Bi$_{35}$Te$_{65}$ has also the $R$-3$m$ structure at ambient condition. It remains stable up to 9 GPa at room temperature. The superconducting transition is observed at 6 GPa below 2.9 K. There is no obvious anomaly indicating structural phase transition in both pressure dependence of the electrical resistivity at pressures up to 6 GPa and temperature dependence of it at 6 GPa. It suggests that the superconducting transition at 6 GPa of Bi$_{35}$Te$_{65}$ occurs in the $R$-3$m$ structure.