Superconductivity in Cu x Bi 2 Se 3 and its Implications for Pairing in the Undoped Topological Insulator

${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ layers, yielding an electron concentration of $\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$, results in superconductivity at 3.8 K in ${\mathrm{Cu}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ for $0.12\ensuremath{\le}x\ensuremath{\le}0.15$. This demonstrates that Cooper pairing is possible in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ at accessible temperatures, with implications for studying the physics of topological insulators and potential devices.