Unconventional superconductivity and the electronic structure of 4Hb-TaS2

In transition-metal dichalcogenides the proximity between layers of broken inversion symmetry with strong spin–orbit coupling and layers of strongly correlated electrons provides a platform for studies of newly discovered phases. 

Anomalous magnetic memory effect, topological superconductivity and broken time reversal symmetry are among the novel phases found and measured in 4Hb-TaS2. Among other phases believed to exist in this material is chiral-triplet superconductivity, which could provide a platform for realizing Majorana edge modes. However, so far no clear evidence has been shown for such pairing.

We present, using the Little-Parks experiment, evidence for an unconventional order parameter in 4Hb-TaS2. We find a pi shift in the Little-Parks oscillations, an unambiguous indication of a two-component order parameter.

In addition, we find that in the presence of an in-plane magnetic field the transition temperature increases upon the application of an out-of-plane field as expected for certain chiral superconductors.  Furthermore, using ARPES and DFT we show that the band structure of 4Hb-TaS2 is substantially different from that of the constituents 2H-TaS2 and 1T-TaS2. We show that the proximity between layers of strongly correlated electron systems, including superconductivity and a depleted Mott insulator, can bring about other intricate phases such as those in 4Hb-TaS2.