Unconventional Anisotropic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>s</mml:mi></mml:math>-Wave Superconducting Gaps of the LiFeAs Iron-Pnictide Superconductor

Umezawa, Keitaro; Li, Y.; Miao, H.; Nakayama, K.; Liu, Z.-H.; Richard, P.; Sato, Takafumi; He, Junbao; Wang, D.-M.; Chen, G. F.; Ding, Hong; Takahashi, Takashi; Wang, S.-C.

doi:10.1103/physrevlett.108.037002

Cited by 168 publications

(175 citation statements)

References 29 publications

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“…In such a state, the gap on one of the α pockets is opposite to that on the γ pocket. In our model, this sign change occurs between the gap on the γ pocket and the outer α pocket, on which the gap has been measured in ARPES experiments 25,26 . (ARPES data obtained by the Dresden group indicates that the inner hole pocket in LiFeAs may actually be buried under the FS 25 .)…”

Section: Ivi S-wave Gap For Unrenormalized Interactionsmentioning

confidence: 71%

“…The gaps do not have nodes, but do show sizeable variations along the FS: the gap on the γ pocket has a cos 4θ variation along the FS 25,26 and the gaps on the two electron β pockets vary nearly as ±| cos 2θ| 25,26 , which is expected when the hybridization between the two β pockets is weak. Probably, the gap on the α pocket also has an angular dependence, but the pocket is too small to detect the angular dependence along it in ARPES measurements 25,26 . The absence of gap nodes rules out pure non-swave states, like d−wave.…”

Section: Arpesmentioning

confidence: 98%

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Superconductivity from repulsion in LiFeAs: Novels-wave symmetry and potential time-reversal symmetry breaking

et al. 2014

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We analyze the structure of the pairing interaction and superconducting gap in LiFeAs by decomposing the pairing interaction for various kz cuts into s− and d-wave components and by studying the leading superconducting instabilities. We use the ten orbital tight-binding model, derived from ab-initio LDA calculations with hopping parameters extracted from the fit to ARPES experiments. We find that the pairing interaction almost decouples between two subsets, one consists of the outer hole pocket and two electron pockets, which are quasi-2D and are made largely out of dxy orbital, and the other consists of the two inner hole pockets, which are quasi-3D and are made mostly out of dxz and dyz orbitals. Furthermore, the bare inter-pocket and intra-pocket interactions within each subset are nearly equal. In this situation, small changes in the intra-pocket and inter-pocket interactions due to renormalizations by high-energy fermions give rise to a variety of different gap structures. We focus on s−wave pairing which, as experiments show, is the most likely pairing symmetry in LiFeAs. We find four different configurations of the s−wave gap immediately below Tc: the one in which superconducting gap changes sign between two inner hole pockets and between the outer hole pocket and two electron pockets, the one in which the gap changes sign between two electron pockets and three hole pockets, the one in which the gap on the outer hole pocket differs in sign from the gaps on the other four pockets, and the one in which the gaps on two inner hole pockets have one sign, and the gaps on the outer hole pockets and on electron pockets have different sign. Different s-wave gap configurations emerge depending on whether the renormalized interactions increase attraction within each subset or increase the coupling between particular components of the two subsets. We discuss the phase diagram and experimental probes to determine the structure of the superconducting gap in LiFeAs. We argue that the state with opposite sign of the gaps on the two inner hole pockets has the best overlap with ARPES data. We also argue that at low T , the system may enter into a "mixed" s + is state, in which the phases of the gaps on different pockets differ by less than π and time-reversal symmetry is spontaneously broken.

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Section: Ivi S-wave Gap For Unrenormalized Interactionsmentioning

confidence: 71%

Section: Arpesmentioning

confidence: 98%

Superconductivity from repulsion in LiFeAs: Novels-wave symmetry and potential time-reversal symmetry breaking

et al. 2014

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“…Indeed, Borisenko et al [3] interpreted their ARPES data in the framework of no static or fluctuating magnetic order. This observation would be at odds with the spinfluctuations driven superconductivity leading to an s ± order parameter proposed for iron pnictides in general [27,28], and for LiFeAs in particular [4]. However, a different picture emerges from NMR experiments.…”

Section: Normal State Scatteringmentioning

confidence: 88%

Optical conductivity evidence of clean-limit superconductivity in LiFeAs

et al. 2015

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We measured the optical conductivity of superconducting LiFeAs. In the superconducting state, the formation of the condensate leads to a spectral-weight loss and yields a penetration depth of 225 nm. No sharp signature of the superconducting gap is observed. This suggests that the system is likely in the clean limit. A Drude-Lorentz parametrization of the data in the normal state reveals a quasiparticle scattering rate supportive of spin fluctuations and proximity to a quantum critical point.

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“…• were reported for an electron pocket of LiFeAs, which is attributed to band hybridization and the mixture of (cos k x + cos k y )-term in the gap function [30]. However, none of these could account for the over 50% variation of the gap size in the elliptical Fermi surface of FeSe X as neither SDW nor hybridization is present.…”

mentioning

confidence: 99%

Measurement of an Enhanced Superconducting Phase and a Pronounced Anisotropy of the Energy Gap of a Strained FeSe Single Layer inFeSe/Nb:SrTiO3/KTaO3
Peng
¹
,
Shen
²
,
Xie
³

et al. 2014
Phys. Rev. Lett.
135
12
119
0
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Single-layer FeSe films with extremely expanded in-plane lattice constant of 3.99±0.02 Å are fabricated by epitaxially growing FeSe/Nb:SrTiO 3 /KTaO 3 heterostructures, and studied by in situ angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillion zone corner are resolved with negligible hybridization between them, indicating the symmetry of the low energy electronic structure remains intact as a free-standing single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70 K for the iron based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results put strong constraints on the current theories, and support the coexistence of both even and odd parity spin-singlet pairing channels as classified by the lattice symmetry. [3][4][5]. For these systems, weak coupling theories based on spin-fluctuations predict a dwave pairing symmetry [6,7]. However, it is inconsistent with the isotropic superconducting gap observed by angle resolved photoemission spectroscopy (ARPES) [2,3,8,9], together with evidences for nodeless superconducting gap from specific heat [10], nuclear magnetic resonance [11], etc. On the other hand, the sign preserving s-wave pairing symmetry [12][13][14][15] could not account for the spin-resonance mode found in Rb x Fe 2−y Se 2 by inelastic neutron scattering [16], which suggests the sign change of the superconducting order parameter on different Fermi surface sections [17].To explain the sign changing isotropic gap in e-FeHTSs, several novel pairing scenarios were proposed. For example, it is argued in the bonding-antibonding s ± pairing scenario that with strong hybridization between electron pockets, the two reconstructed electron pockets can have different signs [18]. A further study suggested that this pairing likely coexists with the d-wave to form an s + id-wave pairing symmetry [19]. More recently, the importance of the parity of the 2-Fe unit cell has been emphasized [20], and it has been proposed that there are even and odd parity s-wave spin singlet pairing states, and the coexistence of both states gives a fully gapped state with varied signs in different Fermi surface sections [21,22]. The hybridization between the two electron pockets is not necessary in this scenario. So far, these scenarios could not be convincingly tested, since the detailed structure of the two electron pockets could not be resolved in all known e-FeHTSs.Two recent ARPES studies have found a gap in singlelayer FeSe/STO, which closes at 65 K and suggests a possible record high superconducting transition temperature (T c ) of 65 K for FeHTSs [4,5]; or at least, it is the pair-formation temperature record, if the superconducting transition there is a two dimensional Berezinskii-Kosterlitz-Thouless (BKT) type. Particularly, our previous ARPES study has found that the high T c in single-layer FeSe/STO is in...

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Unconventional Anisotropics-Wave Superconducting Gaps of the LiFeAs Iron-Pnictide Superconductor

Cited by 168 publications

References 29 publications

Superconductivity from repulsion in LiFeAs: Novels-wave symmetry and potential time-reversal symmetry breaking

Superconductivity from repulsion in LiFeAs: Novels-wave symmetry and potential time-reversal symmetry breaking

Optical conductivity evidence of clean-limit superconductivity in LiFeAs

Measurement of an Enhanced Superconducting Phase and a Pronounced Anisotropy of the Energy Gap of a Strained FeSe Single Layer inFeSe/Nb:SrTiO3/KTaO3
Peng
¹
,
Shen
²
,
Xie
³

et al. 2014
Phys. Rev. Lett.
135
12
119
0
View full text Add to dashboard Cite

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Unconventional Anisotropics-Wave Superconducting Gaps of the LiFeAs Iron-Pnictide Superconductor

Cited by 168 publications

References 29 publications

Superconductivity from repulsion in LiFeAs: Novels-wave symmetry and potential time-reversal symmetry breaking

Superconductivity from repulsion in LiFeAs: Novels-wave symmetry and potential time-reversal symmetry breaking

Optical conductivity evidence of clean-limit superconductivity in LiFeAs

Measurement of an Enhanced Superconducting Phase and a Pronounced Anisotropy of the Energy Gap of a Strained FeSe Single Layer inFeSe/Nb:SrTiO3/KTaO3Peng1, Shen2, Xie3 et al. 2014Phys. Rev. Lett.135121190View full textAdd to dashboardCite

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Measurement of an Enhanced Superconducting Phase and a Pronounced Anisotropy of the Energy Gap of a Strained FeSe Single Layer inFeSe/Nb:SrTiO3/KTaO3
Peng
¹
,
Shen
²
,
Xie
³

et al. 2014
Phys. Rev. Lett.
135
12
119
0
View full text Add to dashboard Cite