單晶氧化釕奈米線的普適電導漲落

Abstract

近年來電腦工業進步快速，電子元件越做越小，然而在微小的尺寸下，古典的波茲曼傳輸理論已不適用，電子的傳輸性質必頇加入量子力學的修正，因此量子相位相干現象一直是科學家研究的重點，其中弱局域效應已被研究相當一段時間，並且已被作為決定相位相干時間的有力工具。普適電導漲落屬於另一種量子相位相干現象，相對上有關的文獻較少，然而相關文獻已指出，普適電導漲落具有相當大的研究價值，由於其對雜質移動敏感性，使原子級或次原子級的雜質移動事件可被直接觀察到，可被運用在許多領域。 我們以電子束微影製程製作四點量測電極，量測單一單晶RuO2奈米線的低溫電性，我們看到低溫下電導漲落隨溫度下降而增大的普適電導漲落現象，經分析顯示電導漲落應屬於一維系統，但是在加入熱平均效應的考量後理論與實驗沒有完全一致。另外理論指出在一定磁場下隨時變的普適電導漲落大小應該減小，但是我們沒有發現這個現象。 由電阻隨溫度的變化分析顯示低溫下電阻的異常上升量遠大於弱局域效應與電子-電子相互作用的貢獻，由電阻行為推測可能是二能級近藤效應造成。 我們認為造成普適電導漲落的原因應為奈米線中的點缺陷形成的二能級系統，由電阻隨溫度變化的分析結果也支持此一論點。

Recently, as progresses in computer instustry, the electronic devices are made smaller and smaller. In such small systems, classical Boltzmann transport theorem is not applied and quantum modification must be added. As a result, quantum interference phenomena have been important topics in physics. The weak localization effect has been studied for a long time and has become a convenient tool to determine the dephasing time. On the other hand, there are less articles about universal conductance fluctuations, which has been pointed out having great potential for researches. Due to its sensitivity to mobile impurities, direct observations to atomic or even subatomic movements of impurities is possible and can be applied in many fields. Using the e-beam lithography process to make four-porbe contacts, we measured the electric properties of individual single-crystalline RuO2 nanowires at low temperature. We observed increasing conductance fluctuations as temperature decreased, which has been thought as a feature of universal conductance fluctuations. By analysis, the UCF should come from a one dimension system. But with thermal averaging effect, the data can’t be fit very well. We didn’t observe the reduction of fluctuation magnitude in the present of magnetic field. In R-T data, the increasing resistivity at low temperature was much more larger than the contribution of weak localization effect and electron-electron interaction, and maybe caused by two-level system Kondo effect. We suppose that the universal conductance fluctuations are due to the two-level systems formed by point defects in nanowires. Results of R-T data also support this argument.