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

（1）PLD装置的构建：构建了使用脉冲激光沉积技术的薄膜合成能力。一开始，由于衬底温度不足，我们在薄膜的均匀性方面存在问题。因此，我们通过改变提高衬底温度的方法来改进设备。通过这种改进，我们成功地制备了具有良好超导性能的薄膜。（2）薄膜样品的制备：利用上述装置，我们制备了在相图中较宽范围内具有不同空穴浓度的La-Sr-CuO铜酸盐超导体。作为对这些薄膜的电阻率测量的结果，我们证实了我们的薄膜的温度与载流子浓度的相图与已经在大块单晶中报道的一致。（3）高温超导铜酸盐样品的湿法腐蚀研究：我们尝试了用湿法腐蚀技术，通过使用各种不同的化学溶液，制作出窄的金属丝。昂福尔 关于我们 然而，所有的结果都不成功。（4）聚焦离子束（FIB）技术制作窄导线的研究：我们尝试了聚焦离子束（FIB）光刻技术制作窄导线。然而，不幸的是，我们没有成功地使纳米尺度的线适用于散粒噪声实验。（5）超低接触电阻电接触的开发研究：在这方面也没有得到好的结果。我们强烈地感到，FIB、OLD和电学测量的所有能力都位于同一位置的情况对于氧化物超导体中散粒噪声测量的成功是必不可少的。（6）用超导涨落测量和交流电导率测量（宽带技术）研究高Tc铜氧化物超导体的相图：虽然我们在散粒噪声测量方面没有获得好的结果，但我们用我们自己开发的宽带技术测量了合成薄膜的交流电导率，其中微波频率可以连续变化。在所有欠掺杂样品中，超导电性涨落和超导电性转变都可以完全用二维XY模型来理解。另一方面，对于最佳掺杂的晶体，它在三维XY模型中变化。我们的初步结果表明，过掺杂的样品再次显示出二维行为，这表明最佳掺杂的样品在相图中是非常特殊的。这可能与在几乎最佳掺杂的空穴浓度下可能存在量子临界点有关。少

(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