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Fluctuation-induced conductivity up to μ0 H = 14 T for superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal was evaluated from the measured in-plane electrical resistivity, and it was analyzed by Aslamazov-Larkin (AL) theory for zero magnetic field and Ullah and Dorsey (UD) scaling method for magnetic field. A dimensional crossover of superconducting fluctuations from low-temperature three-dimension to high-temperature two-dimension was observed. When the dimensional crossover occurs, a temperature region in which two-dimensional and three-dimensional fluctuations occur simultaneously was found in the intermediate temperature region.

We measured the in-plane electrical resistivity of pristine and irradiated (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 single crystals in B//c and B//ab up to B = 13 T to study the difference between in-plane and out-of-plane vortex pinning and the effect of proton irradiation on these pinning. The crystal structure analyzed by the selected area electron diffraction was monoclinic in these two samples. Protons incident along the c-axis caused an expansion of the lattice constants a and b. The expansion of the lattice constants significantly increased the c-axis coherence length ξc. The vortex pinning in B//ab is well understood by an intrinsic pinning mechanism, which was attenuated by proton irradiation. On the other hand, the vortex pinning in B//c is well understood by the plastic creep theory due to point defects that are enhanced by proton irradiation.

For newly synthesized hole-doped Ca8.5Na1.5(Pt3As8)(Fe2As2)5 single crystals, we measured the infrared reflectivity spectrum and the magnetic field dependence of magnetoresistivity and Hall resistivity. The results of these two experiments in normal states are well described by two band models. In normal states below 150 K, the optical conductivity spectrum shows the transfer of spectral weights from the mid-infrared region to the near-infrared region by Hund's coupling, a strong correlation effect. Meanwhile, the carrier concentration evaluated by magnetoresistivity and Hall resistivity decreases significantly at 150 K due to the formation of pseudogap. In the superconducting state, the spectral weight in the low frequency region by the superconducting condensate is completely suppressed, which is well analyzed by the generalized Mattis-Bardeen (M-B) model with a two superconducting gap.

The temperature dependence of the electric resistivity measured in various magnetic fields was analyzed by the vortex glass theory and the thermally activated flux motion (TAFM) theory. The vortex glass-to-vortex liquid (GTL) transition Tg obtained from the analysis shows a temperature dependence of BgT=B01-T/Tcm. The vortex liquid region is divided into the critical region existing in a finite temperature region just above Tg and the TAFM region present in the finite temperature region above it. In the critical region, the activation energy is expressed as Ueff=kBTTc-T/(Tc-Tg), whereas in the TAFM region, the activity energy is expressed as temperature-nonlinear UT,B=U0B1-tq. In the GTL transition, (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 maintains the 3D vortex structure without exhibiting dimension crossover of the vortex, but Ca10(Pt3As8)((Fe0.92Pt0.08)2As2)5 exhibits the dimension crossover from the 3D vortex glass to the 2D vortex liquid.

The thermally activated flux flow effect has been studied in epitaxial FeSe0.6Te0.4 thin film grown by a PLD method through the electrical resistivity measurement under various magnetic fields for B//c and B//ab. The results showed that the thermally activated flux flow effect is well described by the nonlinear temperature-dependent activation energy. The evaluated apparent activation energy U0(B) is one order larger than the reported results and showed the double-linearity in both magnetic field directions. Furthermore, the FeSe0.6Te0.4 thin film shows the anisotropy of 5.6 near Tc and 2D-like superconducting behavior in thermally activated flux flow region. In addition, the vortex glass transition and the temperature dependence of the high critical fields were determined. Keywords: Thermally activated flus flow, Apparent activation energy, FeSe0.6Te0.4 thin film

The influence of proton irradiation on the fluctuation-induced magnetoconductivity of high quality FeSe _1− _x Te _x ( x = 0.4, 0.55) (FST) thin films has been investigated. The measurements were performed with magnetic fields up to 13 T applied in the two main crystal directions. The results were interpreted in terms of the Ginzburg–Landau approach for three-dimensional materials under a total-energy cutoff. The analysis shows that properly-tuned proton irradiation does not appreciably affect fundamental superconducting parameters like the T _c value, the upper critical fields or the anisotropy. This has important consequences from the point of view of possible applications due to the enhancement of vortex pinning induced by irradiation.

We have measured the reflectivity spectra of the LiFeAs ( T _c = 17.6 K) single crystal in the temperature range from 4 to 300 K. In the superconducting (SC) state ( T T _c ), the optical conductivity spectra display typical metallic behavior with the Drude-type spectra at low frequencies, but we found that the introduction of the two Drude components best fits the data, indicating the multiband nature of this compound. A theoretical analysis of the low-temperature data ( T = 4 K 200 cm ^−1 ), we have also performed the local-density approximation band calculation and calculated the optical spectra of the interband transitions. This theoretical result provided qualitative agreement with the experimental data below 4000 cm ^−1 .