Hypersonic studies in Low dimensional electronic states with strong correlation

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In this study, we constructed a hypersonic system to measure sound absorptions in microwave frequency range of low dimensional electronic systems with strong correlations. The excitation and detection of hypersonics were too difficult to realize, so that only a few studies were reported on a hypersonic absorption of solids. Our group possesses both ultrasound and microwave techniques, which are fundamentally required to build up the hypersonic system. We developed reentrant cavities with high Q values made of an oxygen free copper to generate and detect hypersonics. Most difficult thing was to control precisely the resonant frequency of the cavity, because the frequency varied with temperatures. A huge amount of times were necessary to develop the control mechanisms. Finally we achieved the frequency control by changing cavity volumes with three manipulators mounted on a top flange of the insert at room temperature. The electric circuits were based on a superheterodyne detection to increase resolution. We carried out longitudinal hypersonic measurements of single crystal quartz with 1 cm on length. First and second echo signals were successfully detected, and the temperature change of the absorption coefficient was identified to follow T^3 dependence.