Observability of superconductivity in Sr-doped Bi2Se3 at the surface using scanning tunneling microscope

Abstract

The superconducting materials family of doped Bi2Se3 remains intensively studied in the field of condensed matter physics due to strong experimental evidence for topologically non-trivial superconductivity in the bulk. However, at the surface of these materials, even the observation of superconductivity itself is still controversial. We use scanning tunneling microscopy (STM) down to 0.4 K to show that on the surface of bulk superconducting SrxBi2Se3, no gap in the density of states is observed around the Fermi energy as long as clean metallic probe tips are used. Nevertheless, using scanning electron microscopy and energy-dispersive X-ray analysis, we find that micron-sized flakes of SrxBi2Se3 are easily transferred from the sample onto the STM probe tip and that such flakes consistently show a superconducting gap in the density of states. We argue that the superconductivity in SrxBi2Se3 crystals does not extend to the surface when the topological surface state (TSS) is intact, but in micro-flakes the TSS has been destroyed due to strain and allows the superconductivity to extend to the surface. To understand this phenomenon, we propose that the local electric field, always found in electron doped Bi2Se3 in the presence of the TSS due to an intrinsic upward band bending, works against superconductivity at the surface.

13 pages, 8 figures, to appear in Phys. Rev. Materials

References in corpus (8)

• Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
• Bulk Fermi surface coexistence with Dirac surface state in Bi${}_2$Se${}_3$: a comparison of photoemission and Shubnikov-de Haas measurements
• Local Measurements of the Superconducting Pairing Symmetry in CuxBi2Se3
• Electrochemical synthesis and superconducting phase diagram of Cu_xBi2Se3
• Nematic superconductivity in doped Bi2Se3 topological superconductors
• Work function of bulk-insulating topological insulator Bi2-xSbxTe3-ySey
• Trigger of the ubiquitous surface band bending in 3D topological insulators
• The Vertical Position of Sr Dopants in the Sr${}_x$Bi${}_2$Se${}_3$ Superconductor

Cited by in corpus (1)

• Atomic Visualization of Bulk and Surface Superconductivity in Weyl Semimetal γ-PtBi2