Y. Oshima

Fermi Surface Study of Quasi-Two-Dimensional Organic Conductors by Magnetooptical Measurements.

Magnetooptical measurements of several quasi-two-dimensional (q2D) organic conductors, which have simple Fermi surface structure, have been performed by using a cavity perturbation technique. Despi...

Microwave EPR spectroscopy of cobalt-doped germanium cuprate

Resonance magnetoabsorption spectra of CuGeO3 single crystals containing 2% Co impurity have been studied in the frequency range 60–360 GHz in magnetic fields of up to 16 T and in the temperature interval 2–60 K with the magnetic field B aligned parallel to the a crystallographic axis. In addition to the Cu2+ chain resonance, a new absorption line (unobserved previously in doped CuGeO3 and deriving apparently from the Co2+ ions) was detected in EPR spectra. Quantitative analysis of the spectra suggests that the spin-Peierls transition occurs in about 10% Cu2+ chains, while the spin-Peierls state in the remaining 90% chains is completely destroyed by cobalt doping. The results obtained reveal considerable deviations from the universally accepted scenario of CuGeO3 doping and are discussed within alternative theoretical models, namely, the quantum critical behavior (based on the EPR theory for quasi-one-dimensional systems) and a three-dimensional antiferromagnet with the Néel temperature lowered by disorder.

Quantum critical point in CuGeO3 doped with magnetic impurities

Abstract Using high frequency (up to 450 GHz ) ESR and low-temperature specific heat measurements we find that insertion of 1% Fe and 2% Co damps spin-Peierls and Neel transitions and for T K may give rise to onset of a quantum critical behaviour characteristic for a Griffiths phase.Abstract Using high frequency (up to 450 GHz ) ESR and low-temperature specific heat measurements we find that insertion of 1% Fe and 2% Co damps spin-Peierls and Neel transitions and for T K may give rise to onset of a quantum critical behaviour characteristic for a Griffiths phase.

Cyclotron resonance study of θ-(BEDT-TTF)2I3

Abstract Cyclotron resonances of θ-(BEDT-TTF) 2 I 3 have been observed for the first time in the frequency region from 40GHz to 315GHz at 1.8K using pulsed magnetic field up to 15T. We observed two cyclotron resonances at 150 and 160GHz, but only one resonance in the other frequency region. Obtained effective masses are 0.97 m e and 2.28 m e , and these effective masses turned out to be smaller than the masses obtained by de Haas oscillation.

High-field magnetooptical measurements of BEDT-TTF salts

Abstract Cyclotron resonances of quasi-two-dimensional (q2D) organic conductor θ-(BEDT-TTF)2I3 have been observed by using strip-line technique at 1.8xa0K and Millimeter Vector Network Analyzer, V- and W-Band Cavity at 0.5xa0K. Two resonances are observed, and the mode coupling in the cavity and angular dependence suggest that they are (q2D) cyclotron resonances. The obtained effective masses 0.96me and 2.13me are assigned to the α and β orbits, respectively.

Fermi surface study of θ-(BEDT-TTF)2I3 by cyclotron resonance measurements

Cyclotron resonances of quasi-two-dimensional organic conductor θ-(BEDT-TTF) 2 I 3 have been observed by using Millimeter Vector Network Analyzer (MVNA), V- and W-Band Cavity at 0.5K. Two resonances are observed, and the mode coupling in the cavity suggests that the resonances are cyclotron resonances. Obtained effective masses 1.03m c and 2.14m c are assigned to be a and β orbits, respectively.

Magneto-optical measurements of β-(BEDT-TTF)2AuI2

Magneto-optical measurements of β-(BEDT-TTF) 2 AuI 2 , which has an isotropic two dimensional Fermi surface in the ab-plane, have been performed at 1.8 K by using cavity perturbation technique with steady magnetic field and mosaic transmission technique with pulsed magnetic field. A cyclotron resonance coming from the quasi two dimensional Fermi surface has been observed in both measurements for H⊥ab-plane. Obtained effective mass was 0.9 m c and this result is smaller than the mass obtained by the Shubnikov-de Haas measurement, which suggests the existence of electron-electron interactions in the system.

Magnetic properties of the fullerene organic compounds in strong magnetic fields

Abstract Magnetisation study of the C60·TMTSF·2CS2 molecular complex in magnetic field up to 47 T for the temperature range 1.8–300 K and ESR spectroscopy of the molecular complex (ET)2C60 at T=1.8 K for the frequency range 60–90 GHz in magnetic field up to 32 T provide the experimental evidence that a paramagnetic centers with the reduced g-factor values g

Magnetooptical measurements of quasi-one-dimensional conductor (DMET)2I3

Magnetooptical measurements of quasi-one-dimensional organic conductor (DMET) 2 I 3 have been performed by using a cavity perturbation technique with Millimeter Vector Network Analyzer (MVNA). Several resonances are observed and these resonances disappear when the magnetic field is applied nearby the conducting b-axis. These resonances seem to come from the periodic modulation of group velocities of the carriers on the quasi-one-dimensional Fermi surface (qlD FS). However, these resonances show a different angular dependence with the Fermi traversal resonance (FTR) or quasi-one-dimensional periodic orbit resonance (q1D POR).