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Title: Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3

Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO3 or STO) substrates have recently shown superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 K), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature Tc, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO3 substrate. Here we report high-resolution angle-resolved photoemission spectroscopy results that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO3 system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO3, which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO3.
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  1. SLAC National Accelerator Laboratory, Menlo Park, CA (United States). SIMES
  2. (United States). Geballe Laboratory for Advanced Materials
  3. Univ. of British Columbia, Vancouver, BC (Canada)
  4. (United States)
  5. SLAC National Accelerator Laboratory, Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource
  6. (United States). Advanced Light Source
  7. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0028-0836
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nature; Journal Volume: 515; Journal Issue: 7526
Macmillan, London
Research Org:
SLAC National Accelerator Laboratory, Menlo Park, CA (United States)
Sponsoring Org:
US DOE Office of Science (DOE SC) Basic Energy Sciences (BES)
Country of Publication:
United States