Resonant Ultrasound Spectroscopy and Supersolid Research

共振超声光谱和超固体研究

• 批准号: 0804105
• 负责人: Julian Maynard
• 金额: $ 33.3万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-11-01 至 2012-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804105&HistoricalAwards=false
• 关键词: Resonant; Ultrasound; Spectroscopy; Supersolid; Research

****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.

* 非技术摘要 * 几乎所有的过程，最重要的是那些用于能源生产和分配的过程，都涉及摩擦或阻力，结果是这些过程遭受显著的能量损失。 然而，现代物理学（特别是量子力学）的一个主要结果是存在绝对没有摩擦或阻力的物质。 值得注意的例子包括超导体，它可以携带电流而没有能量损失，是未来电能应用的候选者，以及超流体，它可以流动而没有粘性。 最近的一个发现是超固体，尽管是固体，但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，有必要对这一现象进行彻底的科学了解。 正如超导体所发现的那样，通过测量物质的弹性特性或其对所施加的力的回弹响应，可以进一步理解“超级”现象。 该奖项支持一个项目，该项目将采用一种测量超固体弹性特性的新方法，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在国家的最先进的方法往往被忽视，但同样重要的是，声学领域。最近在凝聚态物理学中最引人注目的发现之一是对4He的超固态的实验观察。 这是一个令人震惊的现象，它的物理起源仍然是一个谜。 大多数实验研究涉及扭转振荡器，传统的解释是振荡器的固有频率增加表明当电池中的部分氦成为超固体时发生的“损失质量”。 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为零。 另一种可能性是扭转振子的频率增加，因为4He剪切弹性模量增加，最近的实验测量提供了这种可能性的证据。 这项个人研究奖支持一个项目，以精确测量4He弹性常数在一个温度范围内通过超固体转变。共振超声光谱，其中测量的细胞的振动的自然频率，连同一个数值（有限元）模型的细胞，将被用来确定4He的弹性常数。 这项研究将培养年轻科学家掌握声学的新方法。