Signatures of Topological Superconductivity in Bulk Insulating Topological Insulator BiSbTe${}_{1.25}$Se${}_{1.75}$ in Proximity with Superconducting NbSe${}_2$

Abstract

The combination of superconductivity and spin-momentum locking at the interface between an s-wave superconductor and a three-dimensional topological insulator (3D-TI) is predicted to generate exotic p-wave topological superconducting phases that can host Majorana fermions. However, large bulk conductivities of previously investigated 3D-TI samples and Fermi level mismatches between 3D bulk superconductors and 2D topological surface states have thwarted significant progress. Here we employ bulk insulating topological insulators in proximity with two-dimensional superconductor NbSe${}_2$ assembled via Van der Waals epitaxy. Experimentally measured differential conductance yields unusual features including a double-gap spectrum, an intrinsic asymmetry that vanishes with small in-plane magnetic fields and differential conductance ripples at biases significantly larger than the superconducting gap. We explain our results on the basis of proximity induced superconductivity of topological surface states, while also considering possibilities of topologically trivial superconductivity arising from Rashba-type surface states. Our work demonstrates the possibility of obtaining p-wave superconductors by proximity effects on bulk insulating TIs.

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• Inter-orbital Cooper pairing at finite energies in Rashba surface states
• Hybridization mechanism of the dual proximity effect in superconductor-topological insulator interfaces
• Helical Topological Superconducting Pairing at Finite Excitation Energies
• Observation of Dirac-like surface state bands on the top surface of BiSe
• Sn${}_{0.06}$Cr${}_3$Te${}_4$: A Skyrmion Superconductor
• Asymmetric Fraunhofer pattern in Josephson junctions from heterodimensional superlattice V${}_5$S${}_8$
• Conductance Oscillations in a Topological Insulator-Disordered Superconductor Hybrid Interface