Strong Pauli paramagnetic effect in the upper critical field of KCa2Fe4As4F2

Wang, Teng; Zhang, Chi; Xu, Liangcai; Wang, Jinhua; Jiang, Shan; Zhu, Zengwei; Wang, Zhaosheng; Chu, J. J.; Feng, Jinchao; Wang, Lingling; Li, Wei; Hu, Tao; Liu, Xiaosong; Mu, Gang

doi:10.1007/s11433-019-1441-4

Cited by 34 publications

(25 citation statements)

References 45 publications

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“…The measured values, shown in the inset to Fig. 3, are much larger than what is generally found for other IBS of the generalized 122 family, but in line with those reported for the upper critical field in the same system [3] and in K-12442 [52] and close to the typical values found in cuprates [50], as shown in Fig. 4c.…”

Section: Anisotropysupporting

confidence: 90%

Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

et al. 2022

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The 12442 compounds are a recently discovered family of iron-based superconductors, that share several features with the cuprates due to their strongly anisotropic structure, but are so far poorly understood. Here, we report on the gap structure and anisotropy of RbCa2(Fe1−xNix)4As4F2 single crystals, investigated by a combination of directional point-contact Andreev-reflection spectroscopy and coplanar waveguide resonator measurements. Two gaps were identified, with clear signatures of d-wave-like nodal structures which persist upon Ni doping, well described by a two-band d − d state with symmetry-imposed nodes. A large London penetration depth anisotropy was revealed, weakly dependent on temperature and fully compatible with the d − d model.

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Section: Anisotropysupporting

confidence: 90%

Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

et al. 2022

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“…Notable features of this highly anisotropic KCa 2 Fe 4 As 4 F 2 are moderate T c of~34 K, and larger J c , and H c2 compared with 122-type IBSs. Large H c2 //ab above 700 kOe at low temperatures has been evaluated [17], although the irreversibility field (H irr ), which separate zero and finite J c regions, is relatively low [12,16]. The in-plane J c evaluated from the measurement of irreversible magnetization at 2 K under the self-field is 8.2 MA/cm 2 , which is significantly larger compared with that of 122-type IBSs [16].…”

Section: Introductionmentioning

confidence: 95%

Critical Current Density and Vortex Dynamics in Pristine and Irradiated KCa2Fe4As4F2

et al. 2021

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We report the critical current density (Jc) and vortex pinning properties in single crystals of a novel iron-based superconductor (IBS) KCa2Fe4As4F2 with large Jc in the pristine state, before and after introduction of artificial defects by swift-particle irradiation. The effects of 2.6 GeV U and 3 MeV proton irradiations in KCa2Fe4As4F2 single crystals on transition temperature Tc and Jc, including its dose dependence, are systematically studied. Jc~8 MA/cm2 under a self-field at 2 K in the pristine crystal is strongly enhanced up to 19.4 and 17.5 MA/cm2 by irradiation of 2.6 GeV U-ions and 3 MeV protons, respectively. Suppression of Tc and dose dependence of Jc in KCa2Fe4As4F2 is different from that in a representative IBS of (Ba,K)Fe2As2, which can be explained by considering the presence of embedded defects in pristine KCa2Fe4As4F2. The vortex dynamics in the pristine and proton irradiated KCa2Fe4As4F2 single crystals are also investigated from the analyses of the field dependence of Jc and the normalized magnetic relaxation rate. In addition to the contribution of embedded defects, weak collective pinning is considered for comprehensive analyses. Vortex dynamics in KCa2Fe4As4F2 is similar to those in (Ba,K)Fe2As2 to some extent, and different from that in anisotropic Li0.8Fe0.2OHFeSe. Large anisotropy, due to the presence of insulating blocking layers in KCa2Fe4As4F2, which leads to much lower irreversibility field (Hirr) compared with 122-type IBSs, strongly affect the vortex dynamics.

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“…Meanwhile, T c can be slightly enhanced by applying a hydrostatic pressure [10]. Transport measurements in KCa 2 Fe 4 As 4 F 2 (K12442) single crystals suggest that the in-plane upper critical field is dominated by the Pauli paramagnetic effect instead of the orbital effect [11]. Theoretical calculation predicts that there are several hole and electron pockets in the K12442 [8,12,13].…”

Section: Introductionmentioning

confidence: 99%

Single particle tunneling spectroscopy and superconducting gaps in layered iron based superconductor KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$

Duan,

Chen,

Hong

et al. 2021

Preprint

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We perform scanning tunneling microscopy/spectroscopy study on the layered iron based superconductor KCa2Fe4As4F2 with a critical temperature of about 33.5 K. Two types of terminated surfaces are generally observed after cleaving the samples in vacuum. On one commonly obtained surface, we observe a full gap feature with energy gap values close to 4.6 meV. This type of spectrum shows a clean and uniform full gap in space, which indicates the absence of gap nodes in this superconductor. Quasiparticle interference patterns have also been measured, which show no scattering patterns between the hole and tiny electron pockets, but rather an intra-band scattering pattern is observed possibly due to the hole-like α pocket. The Fermi energy of this band is only about 24 ± 6 meV as derived from the energy dispersion result. Meanwhile, impurity induced bound-state peaks can be observed at about ±2.2 meV on some spectra, and the peak value seems to be independent to magnetic field. On the second type of surface which is rarely obtained, the fully gapped feature can still be observed on the tunneling spectra, although multiple gaps are obtained either from a single spectrum or separate ones, and the gap values determined from coherence peaks locate mainly in the range from 4 to 8 meV. Our results clearly indicate multiple and nodeless superconducting gap nature in this layered superconductor KCa2Fe4As4F2, and the superfluid is mainly contributed by the hole-like Fermi surfaces near Γ point. This would inspire further consideration on the effect of the shallow and incipient bands near M point, and help to understand the pairing mechanism in this highly layered iron-based superconductor.

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Strong Pauli paramagnetic effect in the upper critical field of KCa2Fe4As4F2

Cited by 34 publications

References 45 publications

Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

Critical Current Density and Vortex Dynamics in Pristine and Irradiated KCa2Fe4As4F2

Single particle tunneling spectroscopy and superconducting gaps in layered iron based superconductor KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$

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