Superconducting Bi2Te: Pressure-induced universality in the (Bi2)m(Bi2Te3)n series

Using high-pressure magnetotransport techniques we have discovered superconductivity in Bi2Te, a member of the infinitely adaptive (Bi-2)(m)(Bi2Te3)(n) series, whose end members, Bi and Bi2Te3, can be tuned to display topological surface states or superconductivity. Bi2Te has a maximum T-c = 8.6 K at P = 14.5 GPa and goes through multiple high-pressure phase transitions, ultimately collapsing into a bcc structure that suggests a universal behavior across the series. High-pressure magnetoresistance and Hall measurements suggest a semimetal to metal transition near 5.4 GPa, which accompanies the hexagonal to intermediate phase transition seen via x-ray diffraction measurements. In addition, the linearity of H-c2(T) exceeds the Werthamer-Helfand-Hohenberg limit, even in the extreme spin-orbit scattering limit, yet is consistent with other strong spin-orbit materials. Considering these results in combination with similar reports on strong spin-orbit scattering materials seen in the literature, we suggest the need for a new theory that can address the unconventional nature of their superconducting states.