多层石墨烯体系的杂质与磁场效应和转移矩方法的推广

Since it possesses many pronounced physical phenomena and potential application, such as electronic transport, spin manipulation and heat disspation, and its carrier can be described as massless Dirac fermion, graphene becomes one of intensive research fields in condensed matter physics and modern material.There are several important issues to be solved, regarding the electronic transport in graphene, such as the effects of the contact and structure topology. Metallic contacts such as gold, platinum and aluminum were adopted in experiments,while most theoretical works assumed graphite contact, which fails to estimate the effect of contact on transport.Recently, we found an exact solution for single layer graphene connected to quantum wire contacts, based on transfer matrix method developed by our group, and found pronounced effects of the contact and structure topology on transport, whereas the minimal conductivity of armchair and zigzag graphene is finite and zero respectively at the limit of large aspect ratio, and also well explained some relevant experimental observations. This program will adopt transfer matrix method and intensively investigate the effects of the number of layer and intra-layer interaction on the transport in bi- and tri-layer graphene, and the effects of defect, non-uniform structure and external magnetic field on the transport in single-, bi- and tri-layer graphene.

石墨烯具有优异的电输运、自旋调控和热传导等特性，其载流子可以表示为无质量狄拉克费米子，蕴含着丰富的物理和潜在的应用前景，成为凝聚态物理与信息材料的研究热点。在石墨烯的电输运特性方面，有一些重要的物理现象和基本问题需要更加深入的研究，例如电极与拓扑特性的影响等。实验研究通常采用金铂铝等金属电极，而绝大部分理论研究局限于石墨烯电极，难以充分考虑电极对电输运的影响。近年来，基于我们发展的一套转移矩阵方法，我们找到了单层石墨烯与量子线电极连接体系的严格解，发现电极与拓扑特性对输运特性有着极为深刻的影响：在纳米带宽长比率足够大的极限下，扶手椅和锯齿形体系的电导率分别为有限值和零，并很好地解释了一些电输运实验现象。本项目将基于转移矩阵方法，深入研究双层与三层石墨烯体系的电输运特性受层数和层间相互作用等参数的影响，以及缺陷、非均匀结构与外磁场对1-3层石墨烯体系电输运特性的影响，并研究相关现象的机理。

本项目初期研究了金属原子掺杂、修饰原子链对石墨烯纳米带的能带结构、电子输运的影响。应力在石墨烯样品中很普遍，引起石墨烯的结构产生形变，等价于对样品施加赝磁场。在本项目中我们主要研究外加应力对石墨烯纳米带的电子性质的调控作用和切变应力和拉伸应力联合作用对石墨烯电子输运的影响。我们不仅验证观测现象：平行于输运方向的应力减弱导电性能而垂直于输运方向的应力则增强导电性能，而且证实切应变不影响石墨烯样品的导电性能。后者阐明了石墨烯在柔性电极、电子产品中的应用前景。我们还进一步研究了Stone-Wales缺陷在石墨烯纳米带的边缘和电极界面处对石墨烯导电性能的影响。本项目还进一步采取电子传输模式匹配机制，成功地将重整化转移矩阵方法推广研究普适的电极间二维材料的电子输运性质，包括量子线电极、石墨烯电极、多端电极。我们利用第一性原理计算得到的紧束缚参数来研究二硫化钼、硅烯等二维材料的第一性原理电子输运。此工作正在整理，预计2016年投稿发表。通过本项目的资助，我们已发表4篇国际期刊论文，2篇论文被国际期刊录用，1篇论文正在整理中。