MRI: Development of an instrument combining optics, transport and strain for studying quantum matter at low temperatures

物质的电子性质的多样性继续增长，例如最近包括所谓的拓扑绝缘体和石墨烯等层状材料中的各种二维态。在他们的研究中，仔细控制温度和磁场是标准的和必要的，但另一个重要的热力学变量，机械应变，通常被忽略。应变可能会对测量结果产生巨大影响，但通常情况下，样品只是简单地安装或布线，要么没有应变，要么随机地不受控制的内置应变。与此同时，灵敏而强大的光学技术在较低的温度下并与其他技术(如电子传输)结合使用的情况很少见。该项目将开发的仪器将解决这两个问题，使用氦稀释制冷机，将应变和自由空间光学的仔细控制与更传统的测量能力相结合，温度低至0.1K以下。PI团队包括世界领先的光学探头、使用压电换能器施加应变和低温技术方面的专业知识。在完成和测试后，该仪器将作为成本中心运行，并根据华盛顿大学清洁能源研究所的教育和研究计划与其他设施一起进行维护。它将是由多个其他赠款支持的研究的关键设施，包括华盛顿大学新的NSF MRSEC，重点是二维材料的相变。因此，它将加强密歇根大学学生在广泛的材料、物理和技术方面的培训。尽管稀释冰箱是世界各地物理科学实验室的标准设施，但这将是美国太平洋西北部第一次用于凝聚态研究，填补了一个重要的空白，并促进了该地区的量子材料活动。根据这项核磁共振拨款将开发的独特仪器将结合样品中应变的实时控制和灵活的共焦光学系统，在稀释冰箱温度(低于100MK)和强磁场(14T)下具有直流和交流(最高可达微波)的电传输能力。这将使人们能够对量子材料中以前无法访问的状态和现象进行广泛的研究，例如诱导和研究平凡绝缘体和拓扑绝缘体之间的相变，或者奇异超导体中的对称破缺。尺寸小至微米级的样品将安装在定制的低温工作台上，该工作台允许三轴定位并能够施加单轴应变。将开发一种具有机械/压电驱动和应变仪技术的硅芯片盒系统，适当地解决一些挑战，包括压电叠层的热膨胀、量化应变的需要、磁孔内的空间约束、以最小的变形和像差最大化光场大小、隔振和散热以及由于内耗和光吸收而产生的加热。自由空间光学将允许扫描、偏振控制、多光束相干光学光谱以及超快光学光谱和光电流测量。该阶段将包括电力、微波和光纤接入。还将密切注意尽量减少电、磁、振动和光学噪声源，以实现所有参数和电子温度低于100MK的高精度和高分辨率。

The diversity of electronic properties of matter continues to grow, for instance recently to include so-called topological insulators and a wide variety of two-dimensional states in layered materials like graphene. Careful control of temperature and magnetic field is standard and essential in their study, but another important thermodynamic variable, mechanical strain, is usually neglected. Strain can have enormous impact on what is measured, but generally samples are simply mounted or wired up with either no strain or random uncontrolled built-in strain. At the same time, it is rare that sensitive and powerful optical techniques are deployed at lower temperatures and in combination with other techniques such as electrical transport. The instrument to be developed in this project will address both of these issues, combining careful control of strain and free-space optics with more conventional measurement capabilities at temperatures down to below 0.1 K, using a helium dilution refrigerator. The team of PIs includes world-leading expertise in optical probes, application of strain using piezo transducers, and low temperature techniques. After completion and testing, the instrument will be operated as a cost center, and maintained with other facilities under the Education and Research program of the Clean Energy Institute at the University of Washington. It will be a key facility for research supported on multiple other grants, including a new NSF MRSEC at UW having a focus on phase transitions in two-dimensional materials. It will thus enhance training of students at UW in a wide range of materials physics and techniques. Although dilution refrigerators are standard facilities in physical science laboratories worldwide, this will be the first used for condensed matter studies in the US Pacific Northwest, filling an important gap and fostering quantum materials activity in the region.The unique instrument to be developed under this MRI grant will combine real-time control of strain in the sample with a flexible confocal optical system with dc and ac (up to microwave) electrical transport capability at dilution refrigerator temperatures (below 100 mK) and high magnetic fields (14 T). This will enable a wide range of studies of regimes and phenomena in quantum materials that have not been accessible before, for example inducing and studying phase transitions between trivial and topological insulators, or symmetry breaking in exotic superconductors. Samples with dimensions down to the micron scale will be mounted on a custom low-temperature stage which allows three-axis positioning and ability to apply uniaxial strain. A silicon-chip cassette system with mechanical/piezoelectric drive and strain gauge technology is to be developed, properly attacking a number of challenges including thermal expansion of the piezo stacks, the need to quantify the strain, spatial constraints inside the magnet bore, maximizing optical field size with minimal distortion and aberration, vibration isolation and heat sinking, and heating due to internal friction and light absorption. Free-space optics will allow scanning, control of polarization, coherent optical spectroscopy with multiple beams, and ultrafast optical spectroscopy and photocurrent measurements. The stage will include electrical, microwave and fiber-optic access. Close attention will also be paid to minimize electrical, magnetic, vibrational and optical noise sources, to achieve high precision and resolution in all parameters and electron temperatures below 100 mK.