近藤隧道結之微分電導的磁場效應

Abstract

為了瞭解二雜質近藤效應中磁性雜質自旋在氧化層介面排列方式的影響，比較二雜質近藤模型中三種相位的基態之間差異。 我們量測五個參雜釔的穿隧接面，基態對應到二雜質近藤效應中的三種相位。藉由改變磁場方向及大小，量測微分電導G(V,T)和磁阻，升溫至100K後加磁場再降溫量測的方式，討論零場冷與場冷之間的差異。 在定磁場大小改變磁場方向的量測中，我們從數據中發現B=4T和B=-4T的微分電導數據可以重疊。在零場冷與場冷的比較，從數據中可以觀察到兩者之間的微分電導有些微偏移，但因穿隧接面的氧化層容易在升降溫過程中變化，故無法明確說明；而在減去背景訊號的微分電導，零場冷與場冷的數據可以重疊。在磁電阻量測中，RKKY耦合強度越大的樣品出現的磁滯行為越明顯，但基態為Kondo Screened的樣品則完全沒有磁滯。 根據實驗結果，我們的結論為磁性雜質自旋方向與排列不影響二雜質近藤效應，在Kondo Screened沒有磁滯行為，在QCP及RKKY有磁滯行為，且隨著RKKY耦合強度越強，磁滯行為越明顯。

We want to know the impurity moment of Two-impurity Kondo effect in the interface of the oxide layer about the influence of their array. Compare different about the ground state of the three phase of the Two-impurity Kondo model. We measure five tunneling junction that dope Y atom, and their ground state can correspond on three phase in 2IK. We change the direction and magnitude of magnetic field. To measure the differential conductance G(V,T) and magnetoresistance. Then we rise the temperature to 100K, after control magnetic field in 4T we cool temperature again to measure as before we measure. So we can discuss the different between zero-field-cooled and field-cooled. iii In fixed magnitude magnetic field we change the direction and we find the G(V,T) curve can be overlapping at B = 4T and B = -4T. For the compare between the zfc and fc, in our data can observe a small offset in the two G(V,T) curve. But the barrier of the tunneling junction is easy to change when we rise and cool the temperature, so we can’t clearly explain. And we fit the G(V,T) curve, to deduct the background. In fitting data we observe the overlapping peak between zfc and fc. At magnetoresistance, the sample with strong RKKY coupling have obvious magnetic hysteresis, but the sample that ground state is Kondo screened doesn’t have magnetic hysteresis. According to the experimental results, we know the impurity moment’s array and direction is uncorrelated to 2IK effect. At the ground state in Kondo screened doesn’t have magnetic hysteresis, and the ground state in QCP and RKKY have magnetic hysteresis. The magnetic hysteresis is bigger when the RKKY coupling is bigger.