Research on superconductivity transition phenomena of organic conductor through quantum oscillation effects.

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Organic superconductor K, -(BEDT-TTEOsCuCNCS^ exhibits superconducting fluctuation effects enhanced by the inherent layered structure. As a result, the superconductivity transition is smeared with no distinct upper critical field. In order to get insight into the superconductivity transition characteristics, damping due to superconductivity appearing on the quantum oscillations is studied.Superconductivity damping factor appearing on the de Haas-van alphen effect, which was measured as a collaboration project with University of Bristol, is analyzed in terms of the superconducting fluctuation. Up to 0.5K, fluctuating superconductivity gap is clarified quantitatively. Its angle dependence with respect to the direction of the external magnetic field indicates the two-dimensionality of the superconductivity and relevant fluctuation effects. In order to investigate the correlation with the two-dimensionality in the normal state, temperature dependence of the anisotropy of resistivity is measured.The Shubnikovde Haas effect, the quantum oscillation on the resistivity, is measured at ambilent and 2 kbar pressure, under temperature down to 0.55 K and magnetic field up to 9 T generated by the magnet purchased with the grant. The Shubnikovde Haas effect is observed above 6.8 T. In a magnetic field region between 6.8 and 7.3 T, additional damping of the oscillation is found. Under pressure in which superconductivity is suppressed, the damping is absent. This indicates clearly that the damping is caused by the superconductivity. The quantitative analysis is not successful because the magnetic field window is too small at 0.55 K Measurements at further low temperature using dilution' refrigerator is encouraged.Other K-type BEDT-TTF salts and BEDO-TTF salts are also investigated, however, no quantum oscillation effect was measured near the superconductivity transition region, at least down to 0.55 K.