Proximity-effect-induced Superconducting Gap in Topological Surface States - A Point Contact Spectroscopy Study of NbSe₂/Bi₂Se₃ Superconductor-Topological Insulator Heterostructures.

ABSTRACT: Proximity-effect-induced superconductivity was studied in epitaxial topological insulator Bi₂Se₃ thin films grown on superconducting NbSe₂ single crystals. A point contact spectroscopy (PCS) method was used at low temperatures down to 40?mK. An induced superconducting gap in Bi₂Se₃ was observed in the spectra, which decreased with increasing Bi₂Se₃ layer thickness, consistent with the proximity effect in the bulk states of Bi₂Se₃ induced by NbSe₂. At very low temperatures, an extra point contact feature which may correspond to a second energy gap appeared in the spectrum. For a 16 quintuple layer Bi₂Se₃ on NbSe₂ sample, the bulk state gap value near the top surface is ~159 ?eV, while the second gap value is ~120 ?eV at 40?mK. The second gap value decreased with increasing Bi₂Se₃ layer thickness, but the ratio between the second gap and the bulk state gap remained about the same for different Bi₂Se₃ thicknesses. It is plausible that this is due to superconductivity in Bi₂Se₃ topological surface states induced through the bulk states. The two induced gaps in the PCS measurement are consistent with the three-dimensional bulk state and the two-dimensional surface state superconducting gaps observed in the angle-resolved photoemission spectroscopy (ARPES) measurement.

SUBMITTER: Dai W 

PROVIDER: S-EPMC5550495 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature