Resonant Ultrasound Spectroscopy and Supersolid Research

****非技术摘要****几乎所有的过程，最重要的是用于能源生产和分配的过程，都涉及摩擦或阻力，其结果是过程遭受重大的能量损失。然而，现代物理学（特别是量子力学）的一个主要结果是绝对没有摩擦或阻力的物质的存在。值得注意的例子包括超导体，它可以在没有能量损失的情况下传输电流，是未来电能应用的候选者，以及超流体，它可以在没有粘度的情况下流动。最近的一个发现是超固体，尽管它是固体，但它可以像超流体一样流动。这是如何发生的，目前是一个谜，在考虑任何应用之前，对这一现象有一个彻底的科学理解是必要的。正如超导体所发现的那样，对“超级”现象的理解可以通过测量物质的弹性特性或其对施加的力的反弹反应来推进。该奖项支持一个项目，该项目将采用一种新的方法来测量超固体的弹性特性，以增加我们对这种材料的理解。这项研究将培养年轻的科学家，使他们掌握经常被忽视但却很重要的声学领域的最先进的方法。****技术摘要****最近在凝聚态物理中最引人注目的发现之一是实验观察到4He的超固态。这是一个相当惊人的现象，它的物理起源仍然是一个谜。大多数实验研究都涉及到一个扭转振子，传统的解释是，当电池中的部分氦变成超固体时，振子固有频率的增加表明“质量损失”。固体的完全解耦要求固体的剪切弹性模量和剪切粘度完全消失。另一种可能性是，扭转振子的频率增加是因为4He剪切弹性模量增加，最近的实验测量为这种可能性提供了证据。这项个人研究者奖支持了一个项目，该项目旨在精确测量通过超固体转变的温度范围内的4He弹性常数。共振超声光谱学，其中测量细胞的固有振动频率，连同细胞的数值（有限元）模型，将用于确定4He的弹性常数。这项研究将训练年轻科学家使用新的声学方法。

****NON-TECHNICAL ABSTRACT****Virtually all processes, most importantly those used in energy production and distribution, involve friction or resistance, with the consequence that the processes suffer significant losses of energy. However, a major result of modern physics (specifically quantum mechanics) is the existence of substances which have absolutely no friction or resistance. Notable examples include superconductors, which can carry electrical currents with no energy loss and are candidates for future electric energy applications, and superfluids, which can flow without viscosity. A very recent discovery is the supersolid, which despite being a solid, can flow like a superfluid. How this can happen is currently a mystery, and a thorough scientific understanding of the phenomenon is necessary before any applications may be considered. As has been found for superconductors, the understanding of a "super" phenomenon may be advanced through measurements of the substance's elastic properties, or its rebound response to an applied force. This award supports a project that will incorporate a new method for measuring elastic properties of a supersolid in an attempt to increase our understanding of this material. The research will train young scientists in state-of-the-art methods of the often overlooked, but nontheless important, field of acoustics.****TECHNICAL ABSTRACT****One of the most remarkable recent discoveries in condensed matter physics has been the experimental observation of a supersolid state for 4He. It is quite an astounding phenomenon, and its physical origin remains a mystery. Most experimental studies involve a torsional oscillator, with the conventional interpretation that an increase in the oscillator's natural frequency indicates a "lost mass" which occurs when part of the helium in the cell becomes supersolid. Complete decoupling of a solid requires that the solid's shear elastic modulus and its shear viscosity vanish completely. An alternate possibility is that the frequency of the torsional oscillator increases because the 4He shear elastic modulus increases, and recent experimental measurements provide evidence for this possibility. This individual investigator award supports a project to make precise measurements of the 4He elastic constants over a range of temperatures passing through the supersolid transition. Resonant ultrasound spectroscopy, in which measurements of the cell's natural frequencies of vibration, together with a numerical (finite element) model of the cell, will be used to determine the elastic constants of the 4He. The research will train young scientists in novel methods of acoustics.