Taku Saito

Possible Multiple Gap Superconductivity with Line Nodes in Heavily Hole-Doped Superconductor KFe2As2 Studied by 75As Nuclear Quadrupole Resonance and Specific Heat

We report the 75 As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe 2 As 2 (superconducting transition temperature T c ≃3.5 K). The spin-lattice relaxation rate 1/ T 1 in the superconducting state exhibits a gradual temperature dependence with no coherence peak below T c . The quasiparticle specific heat C QP / T shows a small jump, which is about 30% of the electronic specific heat coefficient just below T c . The C QP / T suggests the existence of low-energy quasiparticle excitation at the lowest measurement temperature T =0.4 K≃ T c /10. The T dependences of 1/ T 1 and C QP / T can be explained by a multiple nodal superconducting gap scenario rather than by a multiple fully gapped s ± -wave scenario determined using simple gap analysis.

Single Crystal Growth and Characterization of the Iron-Based Superconductor KFe2As2 Synthesized by KAs Flux Method

Centimeter-sized platelet single crystals of KFe 2 As 2 were grown using a self-flux method. An encapsulation technique using a commercial stainless steel container allowed the stable crystal growth to last for more than 2 weeks. Ternary K–Fe–As systems with various starting compositions were examined to determine the optimal growth conditions. The employment of KAs flux led to the growth of large single crystals with a typical size of as large as 15 ×10 ×0.4 mm 3 . The grown crystals exhibit a sharp superconducting transition at 3.4 K with the transition width 0.2 K, as well as the very large residual resistivity ratio exceeding 450, evidencing the good sample quality.

Evidence for superconducting gap nodes in the zone-centered hole bands of KFe2As2 from magnetic penetration-depth measurements

Among the iron-based pnictide superconductors the material KFe

Fermi Surface and Mass Enhancement in KFe2As2 from de Haas-van Alphen Effect Measurements

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Incommensurate spin fluctuations in hole-overdoped superconductor KFe2As2.

As

Fermi surface in KFe2As2determined via de Haas–van Alphen oscillation measurements

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Strong Electronic Correlations in Iron Pnictides: Comparison of Optical Spectra for BaFe2As2-Related Compounds

is unusual in that its Fermi surface does not consist of quasi-nested electron and hole pockets. Here we report measurements of the temperature dependent London penetration depth of very clean crystals of this compound with residual resistivity ratio

NMR/NQR and Specific Heat Studies of Iron Pnictide Superconductor KFe2As2

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Thermodynamic Study of Nodal Structure and Multiband Superconductivity of KFe2As2

. We show that the superfluid density at low temperatures exhibits a strong linear-in-temperature dependence which implies that there are line nodes in the energy gap on the large zone-centered hole sheets. The results indicate that KFe

Quasi-Two-Dimensional Fermi Surfaces and Coherent Interlayer Transport in KFe2As2

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