Infrared spectroscopy and nano-imaging of iron arsenide superconductors

非技术摘要：这个项目的目的是促进对非常规超导的理解：在相对较高的温度下，这是一种与完全丧失电阻有关的显著现象。这一活动利用了PI开发的光学纳米成像的新实验能力。该项目中的研究和教育相结合，有助于培养具有凝聚态物理、光学、扫描探针显微镜和材料科学专业知识的高技能人才。国际学生联合会致力于扩大目前在研究生教育中任职人数不足的群体的参与，办法是吸纳来自这些群体中学生比例较大的机构的本科生。该项目有助于加强哥伦比亚大学的研究和教育基础设施。由PI开发的纳米光学仪器支持哥伦比亚大学材料研究科学与工程中心和纽约城市学院的多学科活动。技术摘要：在铁基材料中发现高超导电性表明，这种现象并不像人们曾经认为的那样仅限于铜氧化物，而且可能更普遍。这一突破要求探索铁基超导体的光学性质。红外光谱是PI使用的主要实验方法，它允许人们探测超导的基本特征，包括能隙和超流密度。该项目的另一个目标是研究超导产生的正常状态。本项目致力于探索具有不同掺杂的BaFe2As2和NaFeAs的原型化合物。需要对NaFe1-xCuxAs进行系统的研究，以阐明这些材料中难以捉摸的绝缘态的起源以及神秘的超导体-绝缘体转变的原因。利用纳米光学方法对所研究样品的均匀性进行了验证。将纳米红外成像与同时进行的扫描磁力显微镜测量相结合，探测局部超导，非常适合于揭示超导和密度波态之间相互作用的以前未被探索的真实空间方面。

Nontechnical abstract:This project is aimed at advancing the understanding of unconventional superconductivity: a remarkable phenomenon pertaining to complete loss of resistance at relatively high temperature. This activity capitalizes on novel experimental capabilities for optical nano-imaging developed by the PI. The integration of research and education within this project aids the preparation of highly skilled personnel with expertise spanning condensed matter physics, optics, scanning probe microscopy, and materials science. The PI is committed to broaden participation of groups currently underrepresented in graduate education by engaging undergraduates from institutions with a large fraction of students belonging to these groups. This project contributes to the enhancement of infrastructure for research and education at Columbia. Nano-optical instrumentation developed by the PI supports multidisciplinary activities at Materials Research Science and Engineering Center at Columbia and The City College of New York.Technical abstract:The discovery of high-Tc superconductivity in iron-based materials demonstrates that this phenomenon is not restricted to the copper oxides, as once thought, and is likely to be much more generic. This breakthrough calls for an exploration of the optical properties of iron-based superconductors. Infrared spectroscopy, the principal experimental method employed by the PI, allows one to probe fundamental characteristics of superconductivity including the energy gap and the superfluid density. Another goal of the project is to investigate the normal state, from which superconductivity emerges. This project is focused on the exploration of prototypical BaFe2As2 and NaFeAs compounds with various dopants. Systematic studies of NaFe1-xCuxAs are needed to elucidate the origin of the elusive insulating state in these materials and of the enigmatic superconductor-insulator transition. Nano-optical methods are utilized to verify the uniformity of the studied specimens. A combination of nano-IR imaging with simultaneously performed scanning magnetic force microscopy measurements probing local superconductivity is well suited to uncover previously unexplored real-space aspects of the interplay between superconducting and density wave states.