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

J. J. Lee, F. T. Schmitt, R. G. Moore, S. Johnston, Y. T. Cui, W. Li, M. Yi, Z. K. Liu, M. Hashimoto, Y. Zhang, D. H. Lu, T. P. Devereaux, D. H. Lee, Z. X. Shen

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Abstract

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 kelvin), 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 (refs 5, 6, 7), 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.

Original languageEnglish
Pages (from-to)245-248
Number of pages4
JournalNature
Volume515
Issue number7526
DOIs
StatePublished - Nov 13 2014
Externally publishedYes

Funding

Acknowledgements This work was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. D.-H.L. is supported by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Science, under the Quantum Material programme DE-AC02-05CH11231. Measurements were performed at the Stanford Synchrotron Radiation Lightsource, a national user facility operated byStanford Universityonbehalf of the US Department of Energy, Office of Basic Energy Sciences.

FundersFunder number
U.S. Department of Energy
Office of Science
Basic Energy Sciences
Division of Materials Sciences and EngineeringDE-AC02-05CH11231

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