Ordered Phases of Solid and Liquid 3He in Defined Geometries

这项研究的重点是超流体3He B对比超流体相干长度x小得多的结构的响应。这些结果可以作为理解其他非常规BCS状态（如氧化物超导体）如何响应杂质存在的范例。在这项工作中，将首次通过在平行板阵列中生长气凝胶来测量有序参数的弯曲刚度。在这里，磁场与表面效应竞争以确定序参量的方向。在与布法罗大学的弗兰克·加斯帕里尼的单独合作中，超流体3He密度将在硅衬底上精确蚀刻的通道中进行研究。这将使超流体间隙抑制的首次精确测量成为可能。另一个实验将研究U2D2核自旋有序固体3He中畴壁的迁移率，看看这个系统是否可能成为研究宏观量子隧道的候选者。参与这些项目的研究生将接受超低温制冷技术、核磁共振波谱学和精密仪器设计方面的培训。这种培训使以前的学生能够在学术界、国家实验室和工业领域取得成功。这项工作将研究超流体3He在二氧化硅气凝胶中被直径仅为5纳米的线散射如何改变超流体的性质。这是一个宏观的量子态，直接类似于超导体，特别是高温氧化物超导体。在这两种情况下，杂质散射都会破坏有序态。通过使用核磁共振技术研究在平行板之间的间隙中生长的气凝胶样品中的超流体是如何定向的，将有可能首次测量这种散射如何影响有序态到弯曲态的刚度。在与布法罗大学的Frank Gasparini的单独合作研究中，超流体3He将在硅衬底上蚀刻的明确的窄通道中进行研究。这将允许通过定义良好的、高度受限的几何形状对超流动性的抑制进行精确的首次测量。这些结果应该有助于理解从高温超导体到中子星中的致密物质，各种超流体和超导体是如何受到杂质散射和限制的影响的。该课程的学生学习技术和材料物理学，使他们能够在学术、政府和工业环境中从事职业。

This research focuses on the response of superfluid 3He B to the presence of structures much smaller than the superfluid coherence length, x. These results can serve as a paradigm for understanding how other unconventional BCS states, such as the oxide superconductors, will respond to the presence of impurities. In this work, the bending stiffness of the order parameter will be measured for the first time by growing aerogel within an array of parallel plates. Here the magnetic field competes with surface effects to orient the order parameter. In a separate collaboration with Frank Gasparini of the University of Buffalo, the superfluid 3He density will be studied in channels accurately etched in silicon substrates. This will allow the first accurate measurements of the superfluid gap suppression in well-defined confining geometries. Another experiment will study the mobility of domain walls in U2D2 nuclear spin ordered solid 3He, to see if this system might be a candidate for studying macroscopic quantum tunneling. Graduate students involved in these projects will receive training in ultra-low temperature refrigeration techniques, NMR spectroscopy, and the design of sophisticated apparatus. This training has allowed previous students to go on to successful careers in academia, national laboratories, and industry. %%%This work will study how the scattering of superfluid 3He by strands just 5 nm in diameter in silica aerogels alter the properties of the superfluid. This is a macroscopic quantum state, directly analogous to that in superconductors, particularly the high temperature oxide superconductors. In both cases impurity scattering can destroy the ordered state. By studying how the superfluid is oriented in an aerogel sample grown in the gaps between parallel plates using NMR techniques, it will be possible to measure how this scattering affects the stiffness of the ordered state to bending for the first time. In a separate collaborative study with Frank Gasparini, University of Buffalo, superfluid 3He will be studied in well-defined narrow channels etched in silicon substrates. This will allow an accurate first measurement of the suppression of superfluidity by well defined, highly confining geometries. These results should be useful in understanding how a broad class of superfluids and superconductors will be affected by impurity scattering and confinement, from the high Tc superconductors to the dense matter in neutron stars. Students in this program learn techniques and materials physics that allow them to pursue careers in academe government, and industrial settings.