Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

Torsello, Daniele; Piatti, Erik; Ummarino, Giovanni; Yi, Xiaolei; Xing, Xiangzhuo; Shi, Zhixiang; Ghigo, Gianluca

doi:10.1038/s41535-021-00419-1

Cited by 14 publications

(7 citation statements)

References 59 publications

(101 reference statements)

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“…This latter feature is consistent with single-band superconductors and multigap systems with mainly interband coupling, such as the pnictides. When a multigap superconductor has predominant interband coupling, the superconducting gaps tend to show a gradual decrease and simultaneous closure at T c -as evidenced by PCARS in our samples [40] -and this results in a smooth superfluid density curve. Compared with the µSR experiments on Rb-12442 polycrystals [30], our measurements display a less pronounced curvature at high T and a wider T range where the behavior of ρ S is quite linear, particularly in Ni-doped samples.…”

Section: Coplanar Waveguide Resonator Analysissupporting

confidence: 58%

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Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds

Piatti¹,

Torsello²,

Ghigo³

et al. 2023

Preprint

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The iron-based compounds of the so-called 12442 family are very peculiar in various respects. They originate from the intergrowth of 122 and 1111 building blocks, display a large in-plane vs. out-of-plane anisotropy, possess double layers of FeAs separated by insulating layers, and are generally very similar to double-layer cuprates. Moreover, they are stoichiometric superconductors because of an intrinsic hole doping. Establishing their superconducting properties, and in particular the symmetry of the order parameter, is thus particularly relevant in order to understand to what extent these compounds can be considered as the iron-based counterpart of cuprates. In this work we review the results of various techniques from the current literature and compare them with ours, obtained in Rb-12442 by combining point-contact Andreev-reflection spectroscopy and coplanar waveguide resonator measurements of the superfluid density. It turns out that the compound possesses at least two gaps, one of which is certainly nodal. The compatibility of this result with the theoretically allowed gap structures, as well as with the other results in literature, is discussed in detail.

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Section: Coplanar Waveguide Resonator Analysissupporting

confidence: 58%

“…6 and in Ref. 40. For the following of the discussion, the most important feature of these crystals is their phase purity, that allows us to exclude the possibility of contributions from residual nodal RbFe 2 As 2 phases.…”

Section: A Experimentalmentioning

confidence: 99%

Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds

Piatti¹,

Torsello²,

Ghigo³

et al. 2023

Preprint

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“…In anisotropic superconductors, the

also has two components, which are in-plane London penetration depth,

, and out-of-plane London penetration depth,

. We expect that the same approach, to that described herein for

, should be applied for the temperature-dependent London penetration depth anisotropy,

[ 72 , 125 , 126 , 127 ]. However, the discussion of this topic is far beyond the framework of the current study.…”

Section: Discussionmentioning

confidence: 99%

Intrinsic Coherence Length Anisotropy in Nickelates and Some Iron-Based Superconductors

Talantsev

2023

Materials

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Nickelate superconductors, R1−xAxNiO2 (where R is a rare earth metal and A = Sr, Ca), experimentally discovered in 2019, exhibit many unexplained mysteries, such as the existence of a superconducting state with Tc (up to 18 K) in thin films and yet absent in bulk materials. Another unexplained mystery of nickelates is their temperature-dependent upper critical field, Bc2(T), which can be nicely fitted to two-dimensional (2D) models; however, the deduced film thickness, dsc,GL, exceeds the physical film thickness, dsc, by a manifold. To address the latter, it should be noted that 2D models assume that dsc is less than the in-plane and out-of-plane ground-state coherence lengths, dsc<ξab(0) and dsc<ξc(0), respectively, and, in addition, that the inequality ξc(0)<ξab(0) satisfies. Analysis of the reported experimental Bc2(T) data showed that at least one of these conditions does not satisfy for R1-xAxNiO2 films. This implies that nickelate films are not 2D superconductors, despite the superconducting state being observed only in thin films. Based on this, here we propose an analytical three-dimensional (3D) model for a global data fit of in-plane and out-of-plane Bc2(T) in nickelates. The model is based on a heuristic expression for temperature-dependent coherence length anisotropy: γξ(T)=γξ(0)1−1a×TTc, where a>1 is a unitless free-fitting parameter. The proposed expression for γξ(T), perhaps, has a much broader application because it has been successfully applied to bulk pnictide and chalcogenide superconductors.

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“…Recently, a stochiometric Fe-based superconductor, ACa2Fe4As4F2 (A=K, Rb, Cs) [29] , has attracted attention due to their multiple-layer structures and a high TC of around 30 K. However, its pairing symmetry remains controversial. Several muon-spin relaxation (μsR) measurements [30][31][32] suggested the possible nodal superconducting gaps, while other methods indicated the nodeless gap feature [33][34][35][36][37][38] .…”

Section: Introductionmentioning

confidence: 99%

Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa2Fe4As4F2

Jiang,

Li,

Liao

et al. 2024

Preprint

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Using angle-resolved photoemission spectroscopy, we report the evidence of the observation of a kink structure in the band dispersion of Fe-based superconductor CsCa2Fe4As4F2. The kink shows an orbital selective and momentum dependent behavior, which is located at 15 meV below Fermi level along the Γ - M direction at the band with dxz orbital character and vanishes when approaching the Γ - X direction, correlated with a slight decrease of the superconducting gap. Most importantly, this kink structure disappears when the superconducting gap closes, indicating that the corresponding bosonic mode (~ 9 ± 1 meV) is closely related to superconductivity. However, the origin of this mode remains unidentified, since it cannot be related to phonons or the spin resonance mode (~ 15 meV) observed by inelastic neutron scattering. The behavior of this mode is rather unique and challenges our present understanding of the superconducting paring mechanism of the bilayer FeAs-based superconductors.

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Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

Cited by 14 publications

References 59 publications

Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds

Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds

Intrinsic Coherence Length Anisotropy in Nickelates and Some Iron-Based Superconductors

Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa2Fe4As4F2

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