Gap structure in Fe-based superconductors with accidental nodes: The role of hybridization

Hinojosa, Alberto; Chubukov, Andrey V.

doi:10.1103/physrevb.91.224502

Cited by 6 publications

(14 citation statements)

References 35 publications

(33 reference statements)

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“…The gap values in the T → 0 limit estimated from the ( s + es ) model fitting are: a small s -wave gap of Δ s (0) = 0.25(3) meV and a large anisotropic extended s -wave gap of with α = 0.34. The value of α < 1 obtained here clearly rules out the presence of accidental nodes 38 . Since the obtained isotropic gap value Δ s (0) is very small, a possible anisotropy of this gap would be beyond the resolution of our experiments.…”

Section: Resultssupporting

confidence: 55%

Superconducting gap structure of FeSe

Jiao

Huang

Rößler

et al. 2017

Sci Rep

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The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall “U”-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe.

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Section: Resultssupporting

confidence: 55%

Superconducting gap structure of FeSe

Jiao

Huang

Rößler

et al. 2017

Sci Rep

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“…For instance, magnetic fluctuations peaked at (π, π) would favor the d-wave state [58,59], whereas a momentum-independent electron-phonon interaction would favor the s-wave state. To the best of our knowledge, no sign of (π, π) magnetic order has been observed in FeSe thin films with only electron pockets.…”

Section: Microscopic Modelmentioning

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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“…[32][33][34] More recently, band hybridization has also been proposed to influence the nodal structure of the superconducting gap in iron-based superconductors. [35][36][37][38] On the other hand, consequences of the induced interband pairing have been much less discussed. Pure interband pairing in cold atom and quantum chromodynamics systems has been proposed to give a "breached" regime containing both a superfluid and a normal liquid, 39,40 but in bandhybridized superconductors the interband pairing is also accompanied by (usually large) conventional intraband pairings.…”

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confidence: 99%