Jonathan Ruhman, Department of Physics, Bar Ilan University, Israel

The next LPEM seminar (hybrid format) will be given
Thursday November 10 at 2:00 pm (Paris timeThursday November 10 at 2:00 pm (Paris time)

Unconventional superconductivity in 4Hb-TaS2

4Hb-TaS2 comprises an alternate stack of two-dimensional transition metal dichalcogenides of ’T’ and ’H’ structure. In the bulk form the H structure is metallic and becomes superconducting below 0.7 K, which is considered to be a conventional BCS superconductor. The T structure on the other has an insulating ground state, presumably of the Mott type, which is a spin-liquid candidate. Interestingly, the combination of these two building blocks leads to unconventional superconductivity below 2.6 K. The muon relaxation rate has been found to increase below Tc, there is subgap constant density of states, signatures of edge states and Kondo resonances inside the superconducting state were observed by STM, A mysterious magnetic memory reflected in a spontaneous vortex phase was seen in scanning SQUID measurements and half vortices were observed in the Little-Parks effect. I will discuss the current theoretical understanding of this system and the main open questions. In particular I will discuss the unification of these results by the idea that the superconducting order parameter belongs to a two-component irreducible representation of the relevant point group symmetry, which is a segue to topological superconductivity. I will also discuss the low-energy magnetic properties of the flat band on the T layers and how they affect superconductivity within Abrikosov-Gor’kov theory.

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