S. Takasaki

Crystal growth of organic charge-transfer complexes by electrocrystallization with controlled applied current

Abstract It has been proposed in the past that in electrocrystallization of charge-transfer complexes the current applied through the electrodes must be controlled and kept proportional to the surface area of the growing crystal in order to keep the growth rate of the surface layers constant to obtain good quality crystals with no secondary nucleation of new crystals or defects. According to the concept, we could obtain so large and good quality crystals that the surfaces of crystals of κ-(BEDT-TTF)2Cu(SCN)2, (TMTTF)2Br and (TMTSF)2X (X = ClO4, PF6 and AsF6) obtained by electrocrystallization with controlled applied current were flatter than the ones obtained by a constant applied current.

Depinning of Spin-Density-Wave in (TMTSF)2ClO4

We have performed the electric conductivity measurements in the spin-density-wave (SDW) phase of (TMTSF) 2 ClO 4 to clarify the dynamics of SDW. The temperature dependence of threshold electric fie...

Effect of electrode-materials for electrocrystallization of organic charge-transfer complex (TMTSF)2ClO4

Abstract Several materials (Pt, Au, Pd, Ag, Cu, Ni, glassy carbon, PbO 2 , TiO 2 and SnO 2 –Sb 2 O 3 ) as positive electrode and Pt metal as negative electrode, respectively, were investigated for crystal growth by electrocrystallization, in order to obtain good-quality crystals of (TMTSF) 2 ClO 4 and to reduce the cost of growing crystals.

STM spectroscopy of (BEDT-TTF)2Cu(NCS)2

The superconducting phase of (BEDT-TTF)2Cu(NCS)2 was investigated by the electron tunneling spectroscopy using low temperature STM. The tunneling differential conductance was obtained at the b-c plane of single crystal varying the tip position. The tunneling conductance is reduced to almost zero and flat near zero bias voltage while it is finite inside the gap edge suggesting the gap anisotropy. The obtained curve is not fitted to the BCS density of states nor the simple d-wave. The anisotropic model with finite gap in which Δ(k) varies depending on the direction in k-space is examined. It is suggested that the superconducting gap is finite and highly anisotropic.

Crystal growth of organic charge-transfer complex by electrocrystallization with regulated applied current

Abstract The regulated electrocrystallization of organic charge-transfer complex is presented. By this preparation, large Better quality crystals of κ-(BEDT-TTF) 2 Cu(SCN) 2 and (TMTTF) 2 Br and so on than ones prepared by usual method with constant applied current were obtained.

STM Spectroscopy on κ-(BEDT-TTF)2Cu(NCS)2

The dI/dV-V curves in the superconducting phase of κ-(BEDT-TTF)2Cu(NCS) 2 single crystals have been measured by STM spectroscopy. The tunneling spectra on the lateral surfaces systematically vary depending on the tunneling direction in the b-c plane. This is explained by the d x2-y2 -wave gap model considering the k dependence of the tunneling transition probability. The pseudogap-like behavior is observed at temperatures between T c and 45 K. It is strongly suggested that the pair wave function has the d x2-y2 -wave symmetry in this salt.

Collective Mode of Spin-Density-Wave in (TMTSF)2ClO4.

The conductivity measurements were performed in the spin-density-wave (SDW) phase of (TMTSF) 2 ClO 4 . The electric conductivity increases above the clear threshold electric field E T . The normalized excess electric conductivity [σ(2 E T )-σ(0)]/σ(0) rapidly decreases below about T * ≃0.3 T SDW , where T SDW is the SDW transition temperature. In high electric fields far above E T , the temperature independent electric conduction expressed as the function j = j 0 exp (- E 0 / E ) is observed below T * . It is suggested that the sliding of SDW with the quantum origin occurs in the low temperature. These phenomena are related to the phase transition dividing the SDW phase into two sub-phases in (TMTSF) 2 ClO 4 . The electric conductivity in the low temperature sub-phase is discussed in term of the SDW with the discommensuration.

Direct observation of in-plane gap anisotropy in (BEDT-TTF)2Cu(NCS)2

Abstract The superconducting phase of κ-(BEDT-TTF) 2 Cu(NCS) 2 was investigated by the electron tunneling spectroscopy using low temperature STM. The tunneling differential conductance obtained at the b-c surface shows V-shaped gap structure consistent with the d -wave symmetry. The lateral surface of single crystals was also investigated. We found that the tunneling spectrum varies its shape depending on the tip direction. This indicates the gap anisotropy. Taking into account the k -dependence of the tunneling transition probability, the in-plane anisotropy of the conductance is well explained by the d -wave symmetry with line nodes along the direction 45 ° from the c -axis. The d x 2 − y 2− wave pairing is strongly suggested in this material.

Anion disorder and two-dimensionality in the superconducting and SDW states of (TMTSF){sub 2}ClO{sub 4}

The anion-disorder and two-dimensionality effect for the superconducting and SDW phase of (TMTSF)2ClO4was investigated through static magnetization and resistance measurements for various cooling rates through the CIO4-ClO4-anion ordering temperature. In the slowly cooled phase, we find a strong dependence of the superconducting transition temperature on the a-axis residual resistivity ρa due to the suppression of anion ordering. This behavior supports models of non-s-wave pairing in (TMTSF)2X. In the rapidly quenched phase, the transition temperature of SDW shows a large increase in the magnetic field. This means that the SDW phase of quenched (TMTSF)2ClO4is strongly suppressed by the two-dimensionality of the system.

Quantum Hall transitions in (TMTSF)2PF6.

We have studied the temperature dependence of the integer quantum Hall transitions in the molecular crystal (TMTSF)