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各种各样的二维状态的层状材料，如石墨烯。在它们的研究中，仔细控制温度和磁场是标准的和必不可少的，但另一个重要的热力学变量，机械应变，通常被忽略。应变可能对测量结果产生巨大影响，但通常样品只是简单地安装或连接，没有应变或随机不受控制的内置应变。与此同时，在较低温度下部署敏感和强大的光学技术并与其他技术（如电传输）相结合是罕见的。在这个项目中开发的仪器将解决这两个问题，结合应变和自由空间光学的仔细控制与更传统的测量能力，在温度低至0.1 K以下，使用氦稀释制冷机。PI团队拥有世界领先的光学探头、使用压电传感器的应变应用和低温技术方面的专业知识。完成和测试后，该仪器将作为成本中心运行，并与华盛顿大学清洁能源研究所教育和研究项目下的其他设施一起维护。它将是一个关键的研究设施，支持多个其他赠款，包括一个新的NSF MRSEC在华盛顿大学有一个重点在二维材料的相变。因此，它将加强在UW的学生在广泛的材料物理和技术的培训。尽管稀释制冷机是全球物理科学实验室的标准设施，但这将是美国太平洋西北部首次用于凝聚态研究，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MRI赠款开发的独特仪器将结合联合收割机实时控制样品中的应变与灵活的共焦光学系统，直流和交流（微波）电传输能力在稀释冰箱温度（低于100 mK）和高磁场（14 T）。这将使以前无法访问的量子材料中的制度和现象的广泛研究成为可能，例如诱导和研究平凡和拓扑绝缘体之间的相变，或奇异超导体中的对称性破缺。尺寸低至微米级的样品将安装在定制的低温载物台上，该载物台允许三轴定位和施加单轴应变的能力。将开发具有机械/压电驱动器和应变仪技术的硅芯片盒系统，适当地应对许多挑战，包括压电叠层的热膨胀、量化应变的需要、磁体孔内的空间约束、最大化光场尺寸并具有最小的失真和像差、振动隔离和散热以及由于内部摩擦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、具有多个光束的相干光谱学、以及超快光谱学和光电流测量。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100 mK的高精度和分辨率。

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.