Ultrasonic investigation on BEDT-TTF-based superconductors

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Crystal growth and physical properties of BEDT-TTF related CT complexes were studied. As to the crystal growth study, In situ observation of crystal growth of beta- (BEDT-TTF) _2I_3 by the electrochemical oxidation method was carried out. Stable growth of the seed crystal was observed at the beginning of the growth, while the growth rate was gradually decelerated with passage of time. A measurement of time dependence of the distribution of the anion molecules shows a local decrease in the anion concentration at around the anode. From this, the observed deceleration of the growth could be explained by the shift of the forming location of the charge-transfer complex which is attributed to the decrease of solute concentration.As to the physical properties, the superconducting statewas of kappa- (BEDT-TTF) _2K (SCN) _4 was investigated ultrasonic measurements, and the result was discussed based on the vortex state of this material. The low-temperature anomalous state of alpha- (BEDT-TTF) _2KHg (NCS) _4 was detected by ultrasonic measurements. The results were interpreted by the carrier change in the anomalous state. Thermal conductivity of alpha- (BEDT-TTF) _2I_3 was measured as functions of temperature.