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光谱中超导带隙值的可重复性。在超导体中，Andreev反射的变化依赖于接触尺寸（与相位相干性相关），从而产生过剩电流和次谐波间隙结构。在这项研究中，它是试图改变接触的大小，并取消与检测信号的相位矢量不平衡。为此，采用两相输出振荡器来消除电路中的不平衡电压和不平衡信号相位。点接触式隧道测量装置采用自行研制的自动原位清洗方法，防止污染和针压。作者用垂直浮区法生长了YB_6超导单晶。进行测量以获得在非常低的温度下作为偏置电压的函数的微分电阻率。在两相输出振荡器中可以独立地改变0.1度的相位。采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，难以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。该研究方案同时消除了电压和相位的不平衡，从而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.