Probing and manipulating superconductivity in nanostructures

非技术描述：超导性可以在放松管制的电力市场和减少二氧化碳排放和其他环境影响方面发挥重要作用。高温超导体（HTS）材料的层状结构导致其物理性质特别是其载流能力或临界电流密度Jc的许多显著影响，临界电流密度Jc是电气设备和系统中的许多应用的关键参数。在过去的二十年里，提高Jc一直是世界范围内应用超导领域努力的焦点。特别是，一个长期存在的问题是理论上的depairing限制（Jd）是否可以达到实际的HTS导体通过自组装的纳米结构设计钉扎的磁涡旋。纳米科学的最新进展为高温超导材料的微结构设计提供了新的机会。该项目通过控制纳米级载流子来设计物理性能的方法代表了从传统经验方法的飞跃，在传统经验方法中，HTS材料的开发没有基础物理的精确指导。这种研究也为下一代提供了纳米科学和材料科学领域的前沿教育。技术难题：由于在纳米尺度下可控加工的困难，以及对这种尺度下的物理学缺乏了解，以纳米级精度控制微观结构一直是高温超导材料和其他技术上有趣的材料研究的主要挑战。为了应对这一挑战，几个新的工艺应变工程在纳米级已开发PI？通过先前的NSF支持。特别是，理论建模和数值模拟已经连贯地集成到这项研究中，为纳米结构的操作和制造提供见解和指导。本计画的理论与实验的互补，为了解高温超导奈米结构的成长机制提供了一个有效的途径。这种理解是普遍存在的，最终实现了操纵纳米结构特性的能力。本研究分为三个主题。主题1着重于微观生长机制的研究（成核、引发、演化等）。高温超导YBa_2Cu_3O_7（YBCO）薄膜中纳米管和纳米棒的排列阵列。主题2继续着重于发展理论模型和数值模拟，以深入了解YBCO纳米结构的微观生长机制。扩展建模和模拟，以涵盖大范围的高温超导材料和掺杂杂质有助于解释实验观察，并有助于制造具有特定物理特性的纳米结构。主题3探索石墨烯中的超导性。将研究超导体-石墨烯-超导体结构中无质量2D狄拉克费米子在超导状态下的微观输运行为，例如，Nb-石墨烯-Nb约瑟夫森结。尽管有许多令人兴奋的理论研究，但石墨烯超导电性的实验研究仍处于起步阶段。这种Nb-石墨烯-Nb混合系统可能为探索相对论约瑟夫森效应的物理提供独特的系统。

NON-TECHNICAL DESCRIPTION: Superconductivity can play a significant role in deregulated electricity markets and in lessening carbon dioxide emission and other environmental impacts. The layered structure of high temperature superconductor (HTS) materials result in many dramatic effects in their physical properties especially their current carrying capability, or critical current density, Jc, which is a critical parameter for numerous applications in electrical devices and systems. Raising Jc has been the focus of world-wide efforts in the field of applied superconductivity during the past two decades. In particular, a long-standing question is whether the theoretical depairing limit (Jd) can be reached in practical HTS conductors through self-assembly of nanostructures designed to pin the magnetic vortices. Recent advances in nanoscience have provided fresh opportunities in engineering the microstructures of HTS materials. The approach undertaken in this project of designing physical properties via controlling the charge carriers at the nanoscale represents a leap forward from the traditionally empirical method in which the HTS materials have been developed without a precise guidance of fundamental physics. Such research also provides the forefront of education for the next generation in the fields of nanoscience and material science.TECHNICAL DETAILS: Controlling microstructure with nanoscale precision has been a major challenge in material research of HTS and other technologically interesting materials due to the difficulties in processing controllably at nanoscale, and the lack of understanding of the physics at such a scale. To address this challenge, several novel processes for strain engineering at the nanoscale have been developed in PI?s group through prior NSF support. In particular, theoretical modeling and numerical simulation have been coherently integrated into this research to provide insights and guidance in nanostructure manipulation and fabrication. The complement of theory and experiment continues in this project provides an efficient approach in understanding the growth mechanism of nanostructures of HTS. Such an understanding is ubiquitous to ultimately achieve the capability to manipulate the nanostructure properties. This research divides into three themes. Theme 1 focuses on investigation of the microscopic growth mechanisms (nucleation, initiation, evolution, etc.) of nanostructures such as aligned arrays of nanotubes and nanorods in HTS YBa2Cu3O7 (YBCO) films. Theme 2 continues focuses on developing theoretical models and numerical simulations to provide insight into the microscopic growth mechanism of nanostructures in YBCO. Extending the modeling and simulation to cover a large range of HTS materials and doping impurities helps explain experimental observations and assists in fabricating nanostructures with specific physical properties. Theme 3 explores superconductivity in graphene. The microscopic transport behavior of massless 2D Dirac fermions in the superconducting state will be studied for a superconductor-graphene-superconductor structure, e.g., Nb-graphene-Nb Josephson junctions. Experimental investigation of the superconductivity in graphene is still in its infancy despite of many exciting theoretical studies. This Nb-graphene-Nb hybrid system may provide a unique system for exploring the physics of the relativistic Josephson effect.