| 研究実績の概要 |
Topological materials with superconducting instabilities attract much attention in the community since their nontrivial topology is expected to lead to the formation of Majorana fermions at the surface, which are thought to bear potential for fault-free quantum computing. Here the topological crystalline insulator SnTe was targeted by Indium doping. Single crystals were successfully grown and a collaboration with theory and scanning-tunnel microscopy groups started. Theorists calculated the superconducting critical temperature in low-In-doped SnTe and their gap functions and successfully reproduced experimental results. A publication is currently written.
The closely related system GeTe, which is topologically trivial but exhibits a strong Rashba spin splitting, was also targeted by In doping. In this system, superconductivity was discovered and the superconducting phase diagram mapped out in great detail which appeared to be very different from its (Sn,In)Te counterpart. In (Ge,In)Te, a critical doping concentration xc = 0.12 was identified, where various properties change concurrently, among them charge carrier type, structure, and the emergence of superconductivity with a monotonously increasing Tc for x > xc. Simultaneously a crossover of the In valence state from 3+ to 1+ takes places. This close correlation suggests that the new superconducting phase in this system is a direct consequence of the valence instability of the In dopant. Such instabilities are discussed in literature as a possible source of enhancing Tc values. A publication has been submitted.
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