Kouta Kodama

Vortex Dynamics and Diamagnetic Torque Signals in Two Dimensional Organic Superconductor λ-(BETS)2GaCl4

Resistance and magnetic torque measurements have been performed for a two dimensional organic superconductor λ-(BETS)2GaCl4, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. In magnetic fields along the c-axis (parallel to the conducting layers), the interlayer resistance shows a peak at ∼7 T for large currents in the superconducting state. The peak disappears when the magnetic field is tilted from the layers only by 0.2°, which shows that the peak is caused by the dynamics of the Josephson vortices penetrating in the insulating layers. The current–voltage characteristics show that the depinning current of the Josephson vortices is consistently suppressed at around 7 T. The diamagnetic signal, irreversibility field, and depinning current rapidly decrease with increasing field above ∼10 T at low temperatures. The results suggest that there exists a phase boundary in the superconducting state, likely a transition to a Fulde–Ferrell–Larkin–Ovchinnikov phase.

Orbital Effect on FFLO Phase and Energy Dissipation due to Vortex Dynamics in Magnetic-Field-Induced Superconductor λ-(BETS)2FeCl4

Resistance measurements have been performed for a two-dimensional magnetic-field-induced superconductor λ-(BETS)2FeCl4, where BETS denotes bis(ethylenedithio)tetraselenafulvalene. In magnetic fields along the \(c\)-axis (parallel to the conducting layers), characteristic dip structures in the interlayer resistance are observed up to 24.2 T, ascribed to the commensurability effect between the Josephson vortex lattice and periodic oscillation of the order parameter of the Fulde and Ferrell, and Larkin and Ovchinnikov (FFLO) phase. The dip structures disappear when the magnetic field is tilted from the layers only by 1°, showing that the FFLO phase is removed by the orbital effect. When the field is nearly parallel to the layers, the resistance in the superconducting state becomes significantly larger than the normal state value, showing the presence of peculiar vortex dynamics.

Cyclotron resonance and mass enhancement by electron correlation in KFe2As2.

Cyclotron resonance (CR) measurements for the Fe-based superconductor KFe(2)As(2) are performed. One signal for CR is observed, and is attributed to the two-dimensional α Fermi surface at the Γ point. We found a large discrepancy in the effective masses of CR [(3.4±0.05)m(e) (m(e) is the free-electron mass)] and de Haas-van Alphen results, a direct evidence of mass enhancement due to electronic correlation. A comparison of the CR and de Haas-van Alphen results shows that both intra- and interband electronic correlations contribute to the mass enhancement in KFe(2)As(2).

Anisotropic magnetic form factor in a detwinned single crystal of BaFe 2 As 2

We have performed neutron diffraction measurement on a single crystal of parent compound of iron-based superconductor, BaFe

Effects of Pressure and Magnetic Field on the Pressure-Induced Superconductivity in EuFe2As2

_2

High-Pressure Electrical Resistivity Measurements of EuFe2As2 Single Crystals

As

Cyclotron Resonance in Fe-based Superconductor KFe2As2

_2

Highly nonlinear current-voltage characteristics of the organic Mott insulatorκ-(BEDT-TTF)2Cu[N(CN)2]Cl

at 12~K. In order to investigate in-plane anisotropy of magnetic form factor in the antiferromagnetic phase, the detwinned single crystal is used in the measurement. The magnetic structure factor and magnetic form factor are well explained by the spin densities consisting of

Kosterlitz-Thouless-type transition in a charge ordered state of the layered organic conductor α-(BEDT-TTF)2I3.

3d_{yz}

Large energy dissipation due to vortex dynamics in mesoscopic Al disks

electrons with a fraction of about 40~\% and the electrons in the other four