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Zero Point Vacanty and Nuclear Magnetism of Adsorbed Two Dimensional Quantum Solid

吸附二维量子固体的零点空位与核磁性

基本信息

批准号：
13640349
负责人：
MORISHITA Masashi
金额：
$ 2.3万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640349/
关键词：
2D quantum spin system Helium-3 multiple spin exchange interaction zero point vacancy adsorption structure domain wall structure honeycomb cage structure C-IC transition 量子固体

项目摘要

The submonolayer ^3He solid film adsorbed on a graphite surface is one of the most ideal two-dimensional quantum spin system. The magnetism of this system is understood to be governed by the competition of the multiple spin exchange interactions. However, the detail of the competition had not been understood. We have considered that the corrugation of the adsorption potential plays an important role on the competition, and determined the structural phase diagram based on the calculation of the adsorption potential by the path integral Monte Carlo simulations. With increasing density from the √<3>×√<3> phase, striped domain wall structure, honeycomb domain wall structure, honeycomb cage structure and incommensurate structure appear successively. These transitions are the second order structural phase transitions. The obtained structural phase diagram can explain many experimental observations qualitatively. Especially, the sudden AFM - FM change with increasing density, which was the bi … More g puzzle, can be explained as the sudden change of competition due to the structural phase transition from the commensurate structure to the incommensurate one (C-IC transtion).On the other hand, we have measured the heat capacities of these systems down to 100 μK, and observed anomalous temperature dependence, which are almost inversely proportional to the temperature, in a wide density regime and in a wide temperature range more than two orders of magnitude. In any localized spin system, the heat capacity at the high temperature limit must be inversely proportional to the square of temperature. The difference of the observed exponent from the expected normal value, -2, are thought to be a frustration parameter, which show the strength of the competiton of the multiple spin exchange interactions. The observed heat capacity exponent shows complicated behavior with the density. This behavior can also be explained by our proposed phase diagram. The facts that at the lower density range than the √<3>×√<3> phase the competition become weaker and that the no heat capacity contribution from the fluid but the bumps are observed at same density range, strongly support the existence of the zero point vacancy, for which no direct evidence had been observed. Less

吸附在石墨表面的^3He固体亚单层膜是最理想的二维量子自旋系统之一。这个系统的磁性被理解为由多个自旋交换相互作用的竞争所支配。只是，具体的比试，还没有弄清楚。我们认为吸附势的变化对竞争起着重要的作用，并通过路径积分Monte Carlo模拟计算了吸附势，确定了结构相图。从α × β相开始，随着密度的增加<3><3>，依次出现条纹畴壁结构、蜂窝畴壁结构、蜂窝笼结构和无公度结构。这些相变是二级结构相变。所得到的结构相图可以定性地解释许多实验观察结果。特别是随着密度的增加，原子力显微镜-原子力显微镜的突变，这是双折射率 ...更多信息 g难题，可以解释为由于结构相变从公度结构到非公度结构引起的竞争突变另一方面，我们测量了这些系统的热容，直到100 μK，并观察到反常的温度依赖性，这几乎与温度成反比，在宽的密度范围和宽的温度范围内，超过两个数量级。在任何定域自旋系统中，高温极限下的热容必须与温度的平方成反比。观测指数与期望正常值之差-2被认为是一个阻挫参数，它反映了多重自旋交换相互作用的竞争强度。观察到的热容指数与密度表现出复杂的行为。这种行为也可以用我们提出的相图来解释。在比α × β相低的密度范围内<3><3>，竞争减弱，在相同的密度范围内，除了凸点外，没有流体的热容贡献，这一事实有力地支持了零点空位的存在，而这一点没有直接的证据。少