Condensed Matter Seminar Series

Maxim Khodas

Racah Institute of Physics, Hebrew University

Spin-orbit assisted superconductivity in transition metal dichalcogenides 

Mono- and few-layer transition metal dichalcogenides (TMDs) are two-dimensional superconductors with the transition temperature of a few Kelvins. These superconductors have an extremely anisotropic critical magnetic field with the parallel critical field far above the Pauli limit. The mono-layer TMDs are non-centrosymmetric with strong spin-orbit interaction polarizing spins out-of-plane. 

The spin-orbit interaction protects the conventional spin-singlet superconductivity against the pair breaking by the magnetic field. We argue that in addition, the spin-orbit interaction mediates the transformation of singlet Cooper pairs into the triplet Cooper pairs by the applied field. These parallel spin triplets are distinct from the anti-parallel spin triplets present at zero magnetic field. Since the parallel spin triplets are field induced, they have a strong effect on the critical field. Besides, these spin triplets are protected against the disorder scattering thanks to their strong coupling with the spin singlets. In recent experiments two-fold transport anisotropies have been reported inconsistent with the hexagonal symmetry of the underlying lattice. We list possible scenarios of the two-fold symmetry based on pairing of conventional as well as unconventional symmetry. Finally, I discuss the manifestations of the field induced topological phase transition in the 4-pi periodic current phase relation of the TMD based planar Josephson junctions.