Woo-Jae Choi

Vortex fluctuation effect evaluated using reversible magnetization in optimally doped single crystal NaFe0.97Co0.03As superconductor

The reversible magnetization curves for various magnetic fields are investigated for a single crystal of the optimally doped NaFe0.97Co0.03As superconductor with the superconducting transition temperature Tc?=?20.9 K (?(T)?=?0) in the case where H is parallel to c-axis. A well-formed rounding effect is observed in the temperature dependence of the magnetization, and it widens on increasing the strength of the applied magnetic fields. At 20.2 K, we observe a crossing of the M(T) curves for different applied magnetic fields, indicating important fluctuation effects. The irreversibility line Hirr(T) obeys a universal scaling relation Hirr(T)??=??H0(1???T/Tc)n characterized by n?????1.537, which confirms the moderately anisotropic nature of the sample. The scaling analysis of the reversible magnetization in the region near Tc(H) supports the three-dimensional nature of the vortex fluctuations in NaFe0.97Co0.03As.

Thermal activation energy of 3D vortex matter in NaFe 1−x Co x As ( x = 0.01, 0.03 and 0.07) single crystals

We report on the thermally activated flux flow dependency on the doping dependent mixed state in NaFe1−xCoxAs (x = 0.01, 0.03, and 0.07) crystals using the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found clearly that irrespective of the doping ratio, magnetoresistivity showed a distinct tail just above the Tc,offset associated with the thermally activated flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature dependence of the activation energy follows the relation

Superconducting states study in electron-overdoped BaFe1.8Co0.2As2 using terahertz and far-infrared spectroscopy

U(T,B)={U}_{0}(B){(1-T/{T}_{c})}^{q}

Thermally activated flux flow in superconducting epitaxial FeSe0.6Te0.4 thin film

U(T,B)=U0(B)(1−T/Tc)q with q = 1.5 in all studied crystals. The magnetic field dependence of the activation energy follows a power law of

Evidence for a preformed Cooper pair model in the pseudogap spectra of a Ca10(Pt4As8)(Fe2As2)5 single crystal with a nodal superconducting gap

{U}_{0}(B)\sim {B}^{-\alpha }

Thermally activated flux flow in pristine and proton-irradiated Ca 8.5 La 1.5 (Pt 3 As 8 )(Fe 2 As 2 ) 5 single crystals

U0(B)∼B−α where the exponent α is changed from a low value to a high value at a crossover field of B = ∼2 T, indicating the transition from collective to plastic pinning in the crystals. Finally, it is suggested that the 3D vortex phase is the dominant phase in the low temperature region as compared to the TAFF region in our series samples.