Study of elementary charge excitation in strongly correlated materials by shot noise measurment

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(1)Construction of PLD apparatus : A capability of the thin film synthesis using Pulsed laser deposition technique was constructed. In the very beginning, we had problems in the homogeneity of films because of the insufficient substrate temperature. So, we improved the apparatus by changing the method of raising the substrate temperature. By this improvement, we succeeded in making films with good superconductivity properties.(2)Synthesis of thin film samples : Using the above mentioned apparatus, we prepared La-Sr-CuO cuprate superconductors with various hole concentrations for a broad range in the phase diagram. As a result of resistivity measurement on these films, we confirmed that phase diagram of temperature vs carrier concentration of our films agreed well with that already reported in bulk single crystals.(3)Study of wet etching of high-Tc cuprate sample : We tried to make narrow wires by the wet etching techniques, by using various different kinds of chemical solutions. Unfort … More unately, however, all the results were unsuccessful.(4)Study of making narrow wires by FIB technique : We tried to make narrow wires by the focused ion beam (FIB) lithography technique. Unfortunately, however, we did not succeeded in making nano-scale wires applicable in the shot noise experiment.(5)Study of development of electrical contacts with ultra-low contact resistance : We did not get good results for this either. We strongly feel that a circumstance where all the capability of FIB, OLD and those for electrical measurements are located at the same place is indispensable for the success of shot noise measurement in oxide superconductors.(6)Investigation of phase diagram of high-Tc cuprate superconductor by superconductivity fluctuation measurement with ac conductivity measurement (broadband technique) : Although we have not succeeded in obtaining good results for shot noise measurement, we measured ac conductivity of synthesized films by broadband technique developed by our selves, where microwave frequency can be varied in a continuous manner. In all the underdoped samples, the superconductivity fluctuation and superconductivity transition can be understood completely in terms of two dimensional XY model. On the other hand, for optimally doped crystals, it changes in the three dimensional XY model. Our preliminary results show that the overdoped samples show two dimensional behavior again, suggesting that the optimally doped sample is very special in the phase diagram. This may be related to a possible existence of quantum critical point at an almost optimally doped hole concentration. Less