Abstract
The observation of replica bands in single-unit-cell FeSe on SrTiO3 (STO)(001) by angle-resolved photoemission spectroscopy (ARPES) has led to the conjecture that the coupling between FeSe electrons and the STO phonons are responsible for the enhancement of Tc over other FeSe-based superconductors. However the recent observation of a similar superconducting gap in single-unit-cell FeSe/STO(110) raised the question of whether a similar mechanism applies. Here we report the ARPES study of the electronic structure of FeSe/STO(110). Similar to the results in FeSe/STO(001), clear replica bands are observed. We also present a comparative study of STO(001) and STO(110) bare surfaces, and observe similar replica bands separated by approximately the same energy, indicating this coupling is a generic feature of the STO surfaces and interfaces. Our findings suggest that the large superconducting gaps observed in FeSe films grown on different STO surface terminations are likely enhanced by a common mechanism.
Highlights
The observation of replica bands in single-unit-cell FeSe on SrTiO3 (STO)(001) by angle-resolved photoemission spectroscopy (ARPES) has led to the conjecture that the coupling between FeSe electrons and the STO phonons are responsible for the enhancement of Tc over other FeSe-based superconductors
A recent mutual inductance measurement has shown an onset of diamagnetism at the same temperature (65 K) as when a gap emerges in angleresolved photoemission spectroscopy (ARPES), supporting the superconducting origin of the observed single-particle energy gap[2]
Our results show that the electron–phonon replicas at the FeSe/STO(110) interface and bare STO(110) surface are similar to its counterparts at the (001) surface, suggesting such electron–phonon coupling is a generic feature of STO surfaces and interfaces prepared under certain conditions
Summary
The observation of replica bands in single-unit-cell FeSe on SrTiO3 (STO)(001) by angle-resolved photoemission spectroscopy (ARPES) has led to the conjecture that the coupling between FeSe electrons and the STO phonons are responsible for the enhancement of Tc over other FeSe-based superconductors. The recent observation of a similar superconducting gap in single-unit-cell FeSe/STO(110) raised the question of whether a similar mechanism applies. The foremost telling clue concerning the origin of the extra Tc enhancement in 1 UC FeSe/STO(001) comes from the ARPES observation of ‘replica bands’ at B100 meV below the main band[9]. Such replica bands are explained in terms of a ‘shake off’ phenomenon—in the photoemission process of ejecting an electron, part of the incoming photon energy can be used to excite a vibration quantum. Since the (110) surface is geometrically and chemically different from that of (001) surface, it raises doubts[11,12] whether the same electron–phonon-enhancement mechanism applies
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