Aspects of electron–phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO<sub>3</sub>substrates

Wang, Y; Nakatsukasa, Ken; Rademaker, Louk; Berlijn, Tom; Johnston, S.

doi:10.1088/0953-2048/29/5/054009

Cited by 46 publications

(99 citation statements)

References 79 publications

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“…Although such a coupling can certainly enhance T c [20][21][22][23][24], recent experiments indicate that the STO substrate may not be essential to achieve the high-T c state. In particular, T c up to 40 K was observed in electrostatically-gated films of FeSe with different thickness grown both on STO and MgO substrates [25].…”

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confidence: 99%

Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling

Kang

Fernandes

2016

Phys. Rev. Lett.

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The origin of the high-temperature superconducting state observed in FeSe thin films, whose phase diagram displays no sign of magnetic order, remains a hotly debated topic. Here we investigate whether fluctuations arising due to the proximity to a nematic phase, which is observed in the phase diagram of this material, can promote superconductivity. We find that nematic fluctuations alone promote a highly degenerate pairing state, in which both s-wave and d-wave symmetries are equally favored, and Tc is consequently suppressed. However, the presence of a sizable spin-orbit coupling or inversion symmetry-breaking at the film interface lifts this harmful degeneracy and selects the s-wave state, in agreement with recent experimental proposals. The resulting gap function displays a weak anisotropy, which agrees with experiments in monolayer FeSe and intercalated Li1−x(OH)xFeSe.In most iron-based superconductors (FeSC), superconductivity is found in close proximity to a magnetically ordered state, suggesting that magnetic fluctuations play an important role in binding the Cooper pairs [1][2][3][4]. Indeed, the fact that the Fermi surface of these materials is composed of small hole pockets and electron pockets separated by the magnetic ordering vector led to the proposal of a sign-changing s +− wave state, in which the gap function has different signs in the hole and in the electron pockets. However, the recent observation of superconductivity over 70 K in monolayer FeSe brought new challenges to the field [5][6][7][8][9][10][11][12][13][14]. In contrast to the standard FeSC, no long-range magnetic order is observed in thin films or even bulk FeSe [15], and the Fermi surface of monolayer FeSe consists of electron pockets only [6,7,11,16]. Since T c in monolayer FeSe is the highest among all FeSC, the elucidation of its origin is a fundamental step in the search for higher T c in these systems.One of the proposed scenarios to explain the dramatic ten-fold increase of T c in monolayer FeSe with respect to the 8 K value in bulk FeSe [17] was the strong coupling to an optical phonon mode of the SrTiO 3 (STO) substrate [16,18,19], which is manifested by replica bands observed in ARPES [16]. Although such a coupling can certainly enhance T c [20][21][22][23][24], recent experiments indicate that the STO substrate may not be essential to achieve the high-T c state. In particular, T c up to 40 K was observed in electrostatically-gated films of FeSe with different thickness grown both on STO and MgO substrates [25]. Similar values of T c were reported in FeSe coated with potassium [26,27] and in the bulk sample Li 1−x (OH) x FeSe [28,29], which consists of intercalated FeSe layers. In common to all these systems is the fact that their Fermi surface consists of electron pockets only, suggesting that doping by negative charge carriers plays a fundamental role in stabilizing the high-T c state.Importantly, recent experiments in K-coated bulk FeSe [26] revealed that, besides shifting the chemical potential, electron-doping also su...

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confidence: 99%

Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling

Kang

Fernandes

2016

Phys. Rev. Lett.

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“…Arguably, an even more spectacular discovery is the observation of high-temperature superconductivity in a single unit-cell thick layer of FeSe grown epitaxially on SrTiO 3 and BaTiO 3 substrates with a superconducting transition temperature far greater than that of bulk FeSe or that of any other iron-based superconductor [14,17]. As discussed by L Wang et al [14], Y Wang et al [18], and Linscheid [21], the substrate plays a key role in the T C enhancement, possibly through charge transfer, epitaxial strain, or cross-interface electron-phonon coupling. The latter turns out to be strongly momentum dependent and may be very effective in mediating the pairing when the s-wave channel blocked by Coulomb interactions [18].…”

Section: Current Statusmentioning

confidence: 99%

Superconductivity: how the unconventional became the new norm

Weitering

2017

Supercond. Sci. Technol.

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“…In realistic situation, the forward scattering dominates in the finite region of momentum space, with the size In the framework of this model it is rather easy to explain the formation of the "shadow" band in the vicinity of the M point [82,83].…”

Section: Interaction With Optical Phonons In Stomentioning

confidence: 99%

High-temperature superconductivity in FeSe monolayers

Sadovskiǐ

2016

Phys.-Usp.

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This review discusses the main experiments and theoretical views related to observation of high -temperature superconductivity in intercalated FeSe compounds and single layer films of FeSe on substrates like SrTiO 3 . We consider in detail the electronic structure of these systems, both theoretical calculations of this structure at hand and their correspondence with ARPES experiments. It is stressed that electronic spectrum of these systems is qualitatively different from typical picture of the spectrum in well studied FeAs superconductors and the related problems of theoretical description of spectrum formation are also discussed.We also discuss the possible mechanisms of Cooper pairing in monolayers of FeSe and problems appearing here. As single layer films of FeSe on SrTiO 3 can be represented as typical Ginzburg"sandwiches", we analyze the possibility of rising the critical temperature of superconducting transition T c due to different variants of "excitonic" mechanism of superconductivity. It is shown, that in its classic variant (as proposed for such systems by Allender, Bray and Bardeen) this mechanism is unable to explain the observed values of T c , but situation is different when we consider instead of "excitons" the optical phonons in SrTiO 3 (with energy of the order of 100 meV). We consider both the simplest model of T c enhancement due to interaction with such phonons and more specific models with dominant "forward" scattering, which allow to understand the growth of T c as compared with the case of bulk FeSe and intercalated FeSe systems. We also discuss the problems connected with antiadiabatic nature of superconductivity due to such mechanism.

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Aspects of electron–phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO₃substrates

Cited by 46 publications

References 79 publications

Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling

Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling

Superconductivity: how the unconventional became the new norm

High-temperature superconductivity in FeSe monolayers

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Aspects of electron–phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO3substrates

Cited by 46 publications

References 79 publications

Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling

Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling

Superconductivity: how the unconventional became the new norm

High-temperature superconductivity in FeSe monolayers

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Aspects of electron–phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO₃substrates