Superconductivity in intercalated 2D materials

Intercalation is known to be an efficient method for tuning the band structure of layered materials to bring out superconductivity, without significantly altering the crystal structure of the host material. Here, I will present an experimental study of several new superconductors obtained by intercalation of layered materials, including MoS2, black phosphorus and a topological insulator Bi2Se3. We have investigated potassium (K)-intercalated MoS2 and found that doping with K induces both structural and superconducting phase transitions. We demonstrate that all three phases of MoS2-2H, 1T and 1T’-become superconducting as a result of intercalation, with critical temperature Tc of 6.9 K, 2.8 K and 4.6 K, respectively. We also successfully intercalate black phosphorus with several alkali metals (Li, K, Rb, Cs) and alkaline earth metal Ca, and we found superconductivity of intercalated black phosphorus is independent of the intercalant. Superconducting topological insulators, such as Bi2Se3, are regarded as the most promising candidates for topological superconductivity. We report superconductivity in a new family of superconductors derived from Bi2Se3, by intercalation with K, Rb and Cs metals. All three superconductors exhibit qualitatively identical but highly anomalous behaviour of magnetisation, with several new features consistent with the properties of topological superconductors. Specifically, the new materials exhibit a highly unusual extra diamagnetic screening in the Meissner state and two coexisting superconducting phase, including surface superconductivity that we attribute to heavily doped surface states of the original topological insulator (Bi2Se3).