Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunneling microscopy

Abstract

Single-layer FeSe film on SrTiO3(001) was recently found to be the champion of interfacial superconducting systems, with a much enhanced superconductivity than the bulk iron-based superconductors. Its superconducting mechanism is of great interest. Although the film has a simple Fermi surface topology, its pairing symmetry is unsettled. Here by using low-temperature scanning tunneling microscopy (STM), we systematically investigated the superconductivity of single-layer FeSe/SrTiO3(001) films. We observed fully gapped tunneling spectrum and magnetic vortex lattice in the film. Quasi-particle interference (QPI) patterns reveal scatterings between and within the electron pockets, and put constraints on possible pairing symmetries. By introducing impurity atoms onto the sample, we show that the magnetic impurities (Cr, Mn) can locally suppress the superconductivity but the non-magnetic impurities (Zn, Ag and K) cannot. Our results indicate that single-layer FeSe/SrTiO3 has a plain s-wave paring symmetry whose order parameter has the same phase on all Fermi surface sections.

25 pages, 16 figures

References in corpus (6)

• Superconductivity in single-layer films of FeSe with a transition temperature above 100 K
• d-wave pairing from spin fluctuations in the KxFe{2-y}Se2 superconductors
• Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs
• Scanning Tunneling Microscopy/Spectroscopy of Vortices in LiFeAs
• Revealing the Empty-State Electronic Structure of Single-Unit-Cell FeSe/SrTiO${}_3$
• Single Impurity Problem in Iron-Pnictide Superconductors

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