Quantum transport and far from equilibrium response in nano-junctions

纳米结中的量子传输和远离平衡响应

• 批准号: 1961096
• 金额: --
• 依托单位: King's College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1961096
• 关键词: Quantum; transport; far; equilibrium; response

Aim and PlanThis project is about an entirely new low-voltage approach whose electron trans- port characteristics will be investigated theoretically. The experimental partners and collaborators at IBM are building the first nanoscale realization of the PET which makes the theoretical and the experimental progress somewhat hand in hand. The objective is the study of thin film heterostructure at nanometre scales for switching operations including the many-body effects and evaluation of scalability of such technology to low dimensions.The ultimate aim is the development of a state-of-the-art theoretical frame- work for modelling non-equilibrium quantum transport in nanojunctions.Methods and ObjectivesThis theoretical project includes the development and application of atomic scale electronic structure and quantum transport computational techniques to model the conductance of piezoresistive materials in contact with metal electrodes in a device setup. The used methods are based on the density functional theory (DFT), combined with the non-equilibrium Greens functions (NEGF) technique for quantum transport, as implemented in the Smeagol code.Although the electronic structure calculations, in general, are well under- stood and controlled especially using the Density Functional Theory(DFT), the proper description of quantum transport requires more advanced mathematical descriptions e.g., non-equilibrium Keyldysh Green's Functions. In the litera- ture usually Non-Equilibrium Green's Function methods are employed in the framework of DFT to describe transport. It predicts correctly the qualitative nature of reduction in bandgap of these materials with pressure. But the DOS, bandstructure and f-electron conductnces do not agree with experiments. This is because, strong electron-electron correlations are not captured correctly for the highly localised Sm f-shells.Piezoresistive materials such as SmS or SmSe typically include strongly cor- related f-electrons, so that their transport properties cannot be captured by state of the art DFT methods. To be able to describe such systems new algo- rithms are therefore required, which will be based on the dynamical mean field theory (DMFT) embedded in the NEGF framework. DMFT is supposed to re- duce the over-delocalistion of f-electrons and may thus, reduce the conductance overestimation.To date such methods are only in their infancy, and an important aspect of the project will be the development of many-body DMFT+NEGF compu- tational algorithms into a mature software, which will also be distributed for use to the community. Part of the calculations will also be performed with the CASTEP software, and a project to implement DMFT in CASTEP is under way in collaboration with King's College London. The atomic scale con- ductive properties of the piezoresist/metal nanodevices will then be passed to our collaborators and embedded in a multiscale approach encompassing finite elements simulations and analytical models, which will allow to develop new device designs for the experimental partners at IBM.This project is a collaboration between the National Physical Laboratory and Royal Holloway, University of London, as centres for the development of electronic structure methods, where Ivan Rungger and Keith Refson are basedas core developers of the Smeagol and CASTEP software packages, respectively. Collaborators in this project include: IBM TJ Watson (USA), IBM Ruesch- likon (Switzerland), CASTEP developers group (UK), Nano-bio spectroscopy group in the University of the Basque Country (Spain), University of Augsburg (Germany), Kings College London (UK).

目的与计划本项目是关于一种全新的低电压方法，其电子输运特性将从理论上进行研究。IBM的实验合作伙伴和合作者正在构建PET的第一个纳米级实现，这使得理论和实验进展在某种程度上齐头并进。目标是在纳米尺度上研究薄膜异质结构的开关操作，包括多体效应和评估这种技术的可扩展性到低维。最终目标是发展一个国家的最先进的理论框架，用于模拟非纳米结中的平衡量子输运。方法和目的这个理论项目包括原子尺度电子结构的发展和应用，量子输运计算技术，以模拟器件设置中与金属电极接触的压阻材料的电导。所使用的方法是基于密度泛函理论（DFT），结合用于量子输运的非平衡格林函数（NEGF）技术，如在Smeagol代码中实现的。虽然电子结构计算，通常，特别是使用密度泛函理论（DFT），被很好地理解和控制，但是量子输运的适当描述需要更高级的数学描述，例如，非平衡态Keyldysh绿色函数文献中通常在密度泛函理论的框架下采用非平衡绿色函数方法来描述输运。它正确地预测了这些材料的带隙随压力的减少的定性性质。但DOS、能带结构和f电子电导与实验不符。压阻材料如SmS或SmSe通常包括强相关的f-电子，使得它们的输运性质不能被现有技术的DFT方法捕获。为了能够描述这样的系统，因此需要新的算法，这将是基于嵌入在NEGF框架中的动态平均场理论（DMFT）。DMFT被认为可以减少f-电子的过度离域，从而减少电导的高估。到目前为止，这种方法还处于起步阶段，该项目的一个重要方面是将多体DMFT+NEGF计算算法开发成一个成熟的软件，该软件也将分发给社区使用。部分计算也将用CASTEP软件进行，目前正在与伦敦国王学院合作实施一个在CASTEP中实施DMFT的项目。压电抗蚀剂/金属纳米器件的原子尺度导电特性将被传递给我们的合作者，并嵌入到包括有限元模拟和分析模型的多尺度方法中，这将允许为IBM的实验合作伙伴开发新的器件设计。该项目是国家物理实验室和伦敦大学皇家霍洛威之间的合作，作为电子结构方法的发展中心，Ivan Rungger和基思雷夫森分别作为Smeagol和CASTEP软件包的核心开发人员。该项目的合作者包括：IBM TJ沃森（美国）、IBM Ruesch-likon（瑞士）、CASTEP开发人员小组（英国）、巴斯克地区大学的纳米生物光谱学小组（西班牙）、奥格斯堡大学（德国）、伦敦国王学院（英国）。