Establishment of the Reproducibility of the Superconducting Gap in Tunneling measurements.

本研究的目的是建立点接触隧道谱中超导带隙的重现性。在超导体中，安德烈夫反射的变化依赖于接触尺寸(与相干性相关)，从而产生过电流和亚谐带隙结构。在这项研究中，它试图改变触点大小和消除矢量不平衡与被测信号的相位。为此，采用两相输出振荡器来消除电路的不平衡电压和信号相位不平衡。采用自行研制的自动就地清洗方法，建立了点接触隧道测量装置，防止了污染和针压的产生。作者用垂直浮区法生长了YB_6超导体单晶。在很低的温度下进行了测量，得到了作为偏置电压的函数的差动电阻率。可以独立地改变两相输出振荡器中的0.1度的相位。到目前为止，用精密可变电阻代替两相输出振荡器来实现电压平衡。因此，很难控制电路中的相位关系，从而产生不可再现信号或重影信号。通过本课题的研究，同时消除了电压和相位的不平衡，实现了采样信号和电路信号的区分。

The purpose of this research project is to establish the reproducibility of superconducting gap value in the point-contact tunneling spectroscopy. In the superconductor the Andreev-reflection changes depend on the contact size (correlated to the phase coherence) so as to arise the excess current and the subharmonic gap structure. In this study it is tried to change the contact size and to cancel the vector-unbalance with the phase of the detected signal. For this aim the two-phase output oscillator is used to remove the circuit unbalane voltage and the unbalance signal phase. The equipment for the point-contact tunneling measurements was constructed to prevent the contamination and the needle-pressure by the automatic in situ cleaning method developed by us. The superconductor single crystal YB_6 was grown by a vertical floating zone method by an author. The measurements were performed to get the differential resistivity as a function of the bias-voltage at very low temperature. It is possible to change the phase of 0.1 degree in the two phase output oscillator independently. The precise variable resistor was used to get voltage-balance so far instead of the two phase output oscillator. Therefore it was difficult to control the phase relation in the circuit so as to arise the non-reproducible signal or the ghost signal. By this research project the unbalance of the voltage and the phase are removed simultaneously, so that the distinction between the signal from the sample and the signal from the circuit is achieved.