Kazushige Nomura

Non-linear conductivity in the spin density wave phase of (TMTSF)2ClO4

Abstract Electrical conductivity was measured in the spin-density wave phase of (TMTSF)2ClO4, which is induced in zero magnetic field when ordering of ClO4 ions is suppressed by rapid quenching. The conductivity along the one-dimensional axis increases above a threshold field, in the range of 10–40mV cm-1. The threshold field increases slightly with increasing temperature. The conductivity increase is presumably assigned to the sliding motion of the spin-density wave, as suggested by Tomic et al. for (TMTSF)2NO3. Significant sample dependence is observed in threshold field-temperature and conductance-field relations; important effects of the interaction between the deformable spin-density wave and pinning centers are inferred.

Narrow band noise in SDW sliding

Narrow band noise was observed in the spin-density-wave (SDW) phase of quenched (TMTSF)2ClO4, when electric current larger than the threshold for non-ohmicity was passed parallel to the one-dimensional axis. The noise frequency F increases linearly with the excess current density JSDW with a slope FJSDW = 240 kHz (Acm-2)-1. It is confirmed that the non-linear excess current is carried by the SDW condensate and that the narrow band noise is generated by the sliding motion of the SDW.

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...

STM Study of Anisotropic Superconducting Gap of Bi2Sr2CaCu2O8

The electron tunneling study was carried out on Bi 2 Sr 2 CaCu 2 O 8 with use of the scanning tunneling microscope. Both the cleaved and lateral surface of single crystal were investigated. The electronic density of states for the superconducting phase was correctly obtained at the lateral surface. It shows the finite gap on the whole Fermi surface clearly, while the gap has a considerable anisotropy. The temperature dependence of the magnetic field penetration depth was also measured and its thermally activated behavior confirmed the finite gap again. These results indicate the large s -wave component in the pair wave function and the fair contribution of d -wave as well. The attractive force between electrons is not only due to the on-site interaction, but also the extended one.

ANISOTROPIC SUPERCONDUCTING TRANSITION IN ZrTe3

Electrical resistivity and magnetic susceptibility of ZrTe3 were measured. The superconductivity below 2K is found not bulk but of filamentary.

d-wave pair symmetry in the superconductivity of κ-(BEDT-TTF)2X

The superconducting phase of organic superconductors κ-(BEDT-TTF) 2 X was studied by the electron tunneling using scanning tunneling microscope (STM). Tunneling both at the conducting plane and lateral surfaces was performed on single crystals of κ-(BEDT-TTF) 2 Cu(NCS) 2 . Tunneling conductance curve obtained at the conducting plane is explained by the d -wave gap symmetry. The temperature dependence of tunneling spectra is also consistent with the d -wave symmetry. Tunneling spectra at lateral surfaces varies depending on the tunneling direction, suggesting the in-plane anisotropy of the gap. The directional dependence is also consistent with the d -wave symmetry with line nodes π/4 from the k b - and k c -axes. It indicates that the superconducting pair wave function has the d x 2 - y 2 -wave symmetry. (If we take the same conventions for the magnetic Brillouin zone as high- T c cuprates with the d x 2 - y 2 -wave symmetry, the gap symmetry of κ-(BEDT-TTF) 2 Cu(NCS) 2 is the d x y -wave symmetry.) Proto...

Electronic State and Arrangement of Hydrogen Atoms in Ternary Graphite Intercalation Compounds C8KH0.61 –ESR, 1H NMR and 13C NMR Studies

We have studied ESR, 1 H NMR and 13 C NMR in ternary graphite intercalation compounds C 8 KH 0.61 prepared from the highly oriented pyrolitic graphite (HOPG). Although it has been controversial whether the hydrogen atom has a localized moment, our experiment proves non-existence of the localized moment. It is shown that the absorbed hydrogen molecules are dissolved into an atomic state and that the hydrogen atoms have a metallic character. The electronic state of hydrogen atoms and their geometrical arrangement are discussed.

STM study of the electronic density of states in the superconducting phase of Bi2Sr2CaCu2O8

Abstract Tunneling spectroscopic measurement was carried out in the superconducting phase of Bi 2 Sr 2 CaCu 2 O 8 with use of a low temperature scanning tunneling microscope. Both the cleaved Bi-O surface and the lateral surface of a single crystal were investigated. The tunneling conductance shows an explicit superconducting gap structure at both surfaces. For the lateral surface the conductance curve is independent of the tip distance from the sample surface and gives directly the electronic density of states in the superconducting phase. The obtained gap structure is in good agreement with the BCS prediction, although it seems that the gap is slightly anisotropic. The obtained gap-ratio 2Δ/k B T c =6.1 indicates the strong-coupling nature of this superconductor. For the Bi-O surface, on the other hand, the normalized differential conductance increases with increasing the tip distance, especially at the outside of the superconducting gap as reported by Hasegawa et al . Such a dependence on the tip distance is attributed to series barriers of Bi-O, Sr-O layers and vacuum for the tunneling between the Cu-O layer and the tip metal.

STM observation of sliding motion of CDW in K0.3MoO3

Abstract The sliding motion of CDW was investigated with the STM observation in a K0.3MoO3 single crystal. For bias current exceeding the threshold value for CDW depinning, sharp peak was found in the spectra of tunneling current with fixing the tunneling tip position. The peak frequency increased with the current carried by the CDW condensate. This peak was explained by the modulation of tunneling current due to the sliding motion of CDW; the sliding motion of CDW at the surface was observed for the first time. The sliding velocity was obtained directly. It was confirmed that the CDW begins to slide at the surface just above the threshold current with much higher velocity than the interior of sample.

Role of the dimerized gap due to anion ordering in spin-density wave phase of (TMTSF)2ClO4 at high magnetic fields

Magnetoresistance measurements have been carried out along the highly conducting a axis in the FISDW phase of hydrogened and deuterated (TMTSF)