Investigation of Quantum Conductance Fluctuation in Mesoscopic Structure of Degenerate Semiconductor

我们用8.5T超导磁网制作了He^3低温恒温器（0.4K），研究了低温强磁场下介观系统的量子输运。获得了以下结果。(1)在GaAs/AlGaAs异质结的超细细线（有效宽度为170nm）中观察到一维子带的磁减布居效应。(2)在GaAs/AlGaAs异质结的小十字线中观察到非局域电导效应引起的磁场反转下的非对称电导涨落。(3)在样品尺寸和弹性散射长度相当的量子线的弹道输运区，我们观察到零场附近的相关弯曲电阻、非局域电压起伏和磁阻过冲效应。(4)在多端量子线中，我们观察到了Shubnikov-de哈斯（SdH.）在非局部几何结构中，电流探针和电压探针是分开的。S.dH中振幅的衰减长度测量相对于间隔距离的振荡和负弯曲阻力。负弯曲电阻的衰减长度与电子的弹性散射长度近似相等，而与SdH的弹性散射长度近似相等。振荡比散射长度长得多，并且随着磁场的增大而变短。(5)观察到Sb薄膜的安德森局域化。(6)研究了Bi超细细线中的磁阻波动。当导线的长度（L）小于电子的相干长度时，电导涨落不是普适的，并且将随L ^而变化。<-2>

We have made He^3 cryostat (0.4K) with a compact superconducting malenet (8.5T) and investigated the quantum transport of mesoscopic system under low temperatures and high magnetic fields. The following results are obtained.(1) The magnetic depopulation effect of 1-D subbands is observed in the ultrafine narrow wire (the effective width is 170nm) of GaAs/AlGaAs heterostructures.(2) The unsymmetrical conductance fluctuations under a magnetic field inversion due to the non-local conductivity effect is observed in the small cross wire of GaAs/AlGaAs heterostructure.(3) In the ballistic transport region of quantum wire, where the sample size and the elastic scattering length are comparable, we observed the necative bend resistance, the non-local voltage fluctuations and the overshootine, effect of magnetoresistance near zero field.(4) In the multi-terminal quantum wire, we observed the Shubnikov-de Haas (SdH.) effect in the non-local geometry, where the current probes and voltace probes are separated. The decay lengths of amplitudes in the S.dH. oscillation and the negative bend resistance with respect to the separation distance are measured. The decay length of the negative bend resistance is approximately same to the elastic scattering length of electron, however, that of SdH. oscillation is much longer than the scattering length and it becomes shorter with higher magnetic fields.(5) The Anderson localization of Sb film is observed.(6) The magneto-resistance flutuation is investigated in the ultra-fine narrow wire of Bi. When the length of wire(L) is shorter than the coherence length electron the conductance fluctuations are not universal and will diverse as L^<-2>.