Probing and manipulating superconductivity in nanostructures

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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.