Ultrathin Bismuth Film on High-Temperature Cuprate Superconductor BiSrCaCuO as a Candidate of a Topological Superconductor.

One of the key challenges in condensed-matter physics is to establish a topological superconductor that hosts exotic Majorana fermions. Although various heterostructures consisting of conventional BCS (Bardeen-Cooper-Schrieffer) superconductors as well as doped topological insulators were intensively investigated, no conclusive evidence for Majorana fermions has been provided. This is mainly because of their very low superconducting transition temperatures ( T) and small superconducting-gap magnitude.

Ultrathin Bismuth Film on 1T-TaS: Structural Transition and Charge-Density-Wave Proximity Effect.

We have fabricated bismuth (Bi) ultrathin films on a charge-density-wave (CDW) compound 1T-TaS and elucidated electronic states by angle-resolved photoemission spectroscopy and first-principles band-structure calculations. We found that the Bi film on 1T-TaS undergoes a structural transition from (111) to (110) upon reducing the film thickness, accompanied by a drastic change in the energy band structure. We also revealed that while two-bilayer-thick Bi(110) film on Si(111) is characterized by a dispersive band touching the Fermi level ( E), the energy band of the same film on 1T-TaS exhibits holelike dispersion with a finite energy gap at E.