原子分子接面的自旋與非自旋電子與熱流輸運性質與熱電效應

Abstract

本研究計畫以第一原理計算方式，研究原子分子接面的電子與熱流的非平衡態量子輸運性質。主要的研究方法是在密度泛函理論與非平衡態輸運理論(DFT + Lippmann-Schwinger equation)的計算架構下，結合多體物理理論，探討分子接面系統的量子輸運性質與所伴隨的多體物理現象。奈米接面的模型是由兩個半平面無窮大的電極與中間所夾由原子或分子所構成。其中電極部分是以凝膠模型為基礎透過自洽運算求解，偏壓則是由左右電極的化學位所決定。從左與右側電極入射的電子，被中間所夾的原子或分子所散射，此效應則是在DFT + Lippmann-Schwinger equation的架構下做自洽計算得到。 我們的研究子題包含原子分子接面的 (1) 電流電壓特徵曲線 (2) 閘極偏壓可調控之電流(電晶體元件)性質 (3)的熱傳導性質(以分子動力學方式模擬) (4) 電子遂穿所引起的力 (5) 量子噪音 (6) 高階電流的相關函數關係的量子干涉行為 (7) 穿遂電子造成分子振動所造成的奈米結構侷域溫度上升效應 (8) 非彈性散射電子穿隧電流電壓頻譜 (9) 熱電效應與熱能電能轉換機制 (10) 新型態的熱電元件例如致冷機以及利用廢熱驅動分子電晶體的理論模型 (11) 電子與分子振動交互作用對以上問題的影響。我們目前的模型與理論計算，已經能夠處理上述之研究子題。原子和分子接面的電子輸運物理的特性和電極所夾的奈米結構有關，個別原子和分子的特性決定大部分的輸運性質。所以本計畫將在既有的基礎上，繼續深入研究不同的原子和分子接面系統與上述子題相關的量子輸運性質。 過去十年，分子電子學和自旋電子學各自平行發展，成為物理與跨領域科學重要的研究課題。本計畫的另一個主要目標則是結合這兩個領域，朝著分子自旋電子學方向邁進。在現有分子電子學的基礎上，引進電子自旋與自旋軌道偶合，開發新程式和新理論架構，研究原子和分子自旋軌道偶合夾在鐵磁電極中間的自旋電子輸運性質。因為分子元件的微小特性有助於保存傳輸電子的自旋，所以分子自旋電子學將來有潛力形成一個新穎且重要的前瞻性研究領域。

We propose to investigate the quantum transport properties in atomic-scale junctions in the framework of the combination of density-functional theory and Lippmann-Schwinger equation in scattering approaches. We will focus on the current-induced many-body effects in the nanoscale junctions (modeled as electron jellium) formed by atoms/molecule sandwiched between bimetallic electrodes with semi-infinite planar surface. These effects can be calculated from the wavefunctions obtained self-consistently first principles approaches allied to many-body theory. Our research will cover the following subtopics: (1) nonlinear current-voltage characteristics； (2) gate-controllable current in single-molecule transistors； (3) thermal current (simulated by MD)； (4) current-induced force； (5) shot noise； (6) counting statistics； (7) local heating； (8) inelastic electron tunneling spectroscopy (IETS)； (9) thermoelectricity and the energy-conversing mechanism between thermal and electric current； (10) new forms of atomic-scale thermoelectric devices, such and nano-refrigerators, power generators, and self-powered electronic nano-devices； and (11) the effects of electron-vibration interactions on the above mentioned subtopics. In the past decade, we have developed theories and codes to address the above-mentioned subtopics. Owing to the wave nature, the species of individual atom and molecule are critically important to the quantum transport properties in the nanojunctions. We, thus, will continue to investigate the transport properties relevant to the above-mentioned subtopics in various atomic and molecular junctions.Molecular electronics and spintronics emerged around 10 years ago. Both have become the forefront of the multidisciplinary fundamental researches including physics. The alternative major goal of this project is to bridge the gap between molecular electronics and spintronics. We will develop new theories and codes including the ferromagnetic electrodes and spin-orbit potential in the nano-structured object based on our knowledge in molecular electronics to advance the field of ’molecular spintronics.’