Strong anisotropy effect in an iron-based superconductor CaFe<sub>0.882</sub>Co<sub>0.118</sub>AsF

Ma, Yonghui; Ji, Qiu; Hu, Kangkang; Gao, Bo; Li, Wei; Mu, Gang; Xie, Xiaoming

doi:10.1088/1361-6668/aa6fbf

Cited by 18 publications

(18 citation statements)

References 38 publications

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“…The large errors can be ascribed to errors in the sample dimensions, irregular sample shapes and inhomogeneous current distribution. The large anisotropy ρ c /ρ ab of the order of 10 2 is broadly consistent with the large upper-critical-field anisotropy of 9 observed for CaFe 0.882 Co 0.118 AsF [25] as the two anisotropies are approximated by m * c /m * ab and m * c /m * ab , respectively.…”

Section: Temperature Dependence Of Resistivitysupporting

confidence: 80%

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

et al. 2018

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Despite the fact that 1111-type iron arsenides hold the record transition temperature of ironbased superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study, we compehensively determine the Fermi surface in the antiferromagnetic state of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum oscillation measurements and band-structure calculations. The determined Fermi surface consists of a symmetry-related pair of Dirac electron cylinders and a normal hole cylinder. From analyses of quantum-oscillation phases, we demonstrate that the electron cylinders carry a nontrivial Berry phase π. The carrier density is of the order of 10 −3 per Fe. This unusual metallic state with the extremely small carrier density is a consequence of the previously discussed topological feature of the band structure which prevents the antiferromagnetic gap from being a full gap. We also report a nearly linear-in-B magnetoresistance and an anomalous resistivity increase above about 30 T for B c, the latter of which is likely related to the quantum limit of the electron orbit. Intriguingly, the electrical resistivity exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal phase (T > 118 K), which may suggest an incoherent state. Our study provides a detailed knowledge of the Fermi surface in the antiferromagnetic state of 1111 parent compounds and moreover opens up a new possibility to explore Dirac-fermion physics in those compounds.

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Section: Temperature Dependence Of Resistivitysupporting

confidence: 80%

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

et al. 2018

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“…Here λ ab is the penetration depth within the ab plane. Moreover, the Fermi surfaces in the present system are nearly ideal cylinders 27,32 and the in-plane Fermi velocity is rather isotropic within the k x − k y plane. In this case, ρ ab s of the ith Fermi surface can be given by 36…”

Section: Resultsmentioning

confidence: 77%

“…Especially, it was found that the smaller FS around the Γ point (see the α FS in Fig. 4) is much smaller than other FSs around M point and consequently shows a worse nesting condition 27,32 , as compared with the other larger FSs, which should benefit the identification of the abovementioned itinerant and local mechanisms.…”

Section: Introductionmentioning

confidence: 98%

Two-gap superconductivity in CaFe0.88Co0.12AsF revealed by temperature dependence of the lower critical field Hc1c (T)

Wang

et al. 2019

npj Quantum Mater.

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Gap symmetry and structure are crucial issues in understanding the superconducting mechanism of unconventional superconductors. Here we report an in-depth investigation on the out-of-plane lower critical field H c c1 of fluorine-based 1111 system superconductor CaFe 0.88 Co 0.12 AsF with T c = 21 K. A pronounced two-gap feature is revealed by the kink in the temperature dependent H c c1 (T ) curve. The magnitudes of the two gaps are determined to be ∆ 1 = 0.86 meV and ∆ 2 = 4.48 meV, which account for 74% and 26% of the total superfluid density respectively. Our results suggest that the local antiferromagnetic exchange pairing picture is favored compared to the Fermi surface nesting scenario.

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“…The resultant values for the three characteristic fields B ab c2 (in-plane B c2 ), B c c2 (out-of-plane B c2 ) and B P are denoted by arrows in Figure 1c and summarized in Table 1, from which the anisotropy of upper critical field Γ = B ab c2 /B c c2 = 11 is obtained. This value is larger than most of the iron-based superconductors and the copper-based superconductor YBCO 16,19 . Moreover, a clear relative relation B c c2 < B P < B ab c2 can be deduced.…”

Section: Introductionmentioning

confidence: 74%

Unusual evolution of Bc2 and Tc with inclined fields in restacked TaS2 nanosheets

Pan

Guo

et al. 2018

npj Quant Mater

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Recently we reported an enhanced superconductivity in restacked monolayer TaS 2 nanosheets compared with the bulk TaS 2 , pointing to the exotic physical properties of low dimensional systems. Here we tune the superconducting properties of this system with magnetic field along different directions, where a strong Pauli paramagnetic spin-splitting effect is found in this system. Importantly, an unusual enhancement as high as 3.8 times of the upper critical field B c2 , as compered with the Ginzburg-Landau (GL) model and Tinkham model, is observed under the inclined external magnetic field. Moreover, with the out-of-plane field fixed, we find that the superconducting transition temperature T c can be enhanced by increasing the in-plane field and forms a dome-shaped phase diagram. An extended GL model considering the special microstructure with wrinkles was proposed to describe the results. The restacked crystal structure without inversion center along with the strong spin-orbit coupling may also play an important role for our observations. ). Y.H.M. and J.P. contributed equally to this work.Here we present a detailed investigation on the Abrikosov vortex phase of the above-mentioned superconductor, restacked TaS 2 nanosheets, by measuring the conducting properties with magnetic fields along different directions. The in-plane upper critical field B ab c2 is clear larger than the Pauli paramagnetic limiting fields B P , indicating a strong Pauli paramagnetic spin-splitting effects in this material. Importantly, the angle dependence of the upper critical field deviates severely from the Ginzburg-Landau (GL) model and Tinkham model. Moreover, the value of T c is found to increase with the in-plane field B ab under a fixed out-of-plane field B c . Both the intrinsic and extrinsic origins for the observations were discussed and we found that the highly noncentrosymmetric crystal structure, the strong spin-orbit coupling, and the special microstructure with wrinkles are important factors for the unusual behaviors we observed. ResultsDetails regarding the samples preparation and resistance measurements are given in the Methods section. By a careful characterization using combining methods, the structure of the restacked TaS 2 was determined and reported in our previous paper 9 . The inter-layer spacing is close to bulk 2H-TaS 2 , while the 2H symmetry has been broken after the restacking process because of rotations between different layers (see Fig. S1). In such a structure, both the in-plane inversion symmetry in each individual layer and the global inversion symmetry are broken. As a consequent, the inversion symmetry breaking will be severer than the bulk, monolayer, and few layered TaS 2

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Strong anisotropy effect in an iron-based superconductor CaFe_0.882Co_0.118AsF

Cited by 18 publications

References 38 publications

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Two-gap superconductivity in CaFe0.88Co0.12AsF revealed by temperature dependence of the lower critical field Hc1c (T)

Unusual evolution of Bc2 and Tc with inclined fields in restacked TaS2 nanosheets

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Strong anisotropy effect in an iron-based superconductor CaFe0.882Co0.118AsF

Cited by 18 publications

References 38 publications

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Two-gap superconductivity in CaFe0.88Co0.12AsF revealed by temperature dependence of the lower critical field Hc1c (T)

Unusual evolution of Bc2 and Tc with inclined fields in restacked TaS2 nanosheets

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Strong anisotropy effect in an iron-based superconductor CaFe_0.882Co_0.118AsF