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

(1)PLD装置的搭建：建立了脉冲激光沉积技术合成薄膜的能力。在一开始，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对装置进行了改进。薄膜样品的制备：利用上述装置，在较宽的相图范围内制备了不同空穴浓度的La-Sr-CuO超导体。通过对这些薄膜的电阻率测量，我们证实了我们的薄膜的温度-载流子浓度相图与已报道的大块单晶中的相图很好地吻合。(3)高T_c铜酸盐样品的湿法刻蚀研究：我们尝试用各种不同的化学溶液，采用湿法刻蚀技术制作窄线。Unfort…(4)利用聚焦离子束(FIB)技术制作细丝的研究：我们尝试用聚焦离子束(FIB)光刻技术制作细丝。然而，遗憾的是，我们没有成功地将纳米导线应用于散粒噪声实验。(5)超低接触电阻电触头的研制：我们在这方面也没有取得好的结果。我们强烈地感觉到，对于氧化物超导体来说，所有的FIB、OLD和电测量能力都集中在一个地方是必不可少的。(6)利用超导涨落测量和交流电导测量(宽带技术)研究高T_c铜酸盐超导体的相图：虽然我们在测量散粒噪声方面没有取得良好的结果，但我们利用自己开发的宽带技术测量了合成薄膜的交流电导率，这种技术可以连续地改变微波频率。在所有欠掺杂样品中，超导电性涨落和超导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模型中发生变化。我们的初步结果表明，过度掺杂的样品再次表现出二维行为，这表明最佳掺杂的样品在相图上是非常特殊的。这可能与在近乎最佳的空穴掺杂浓度处存在量子临界点有关。较少

(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