Experimental Studies of Nanoscale Energy Localization in Periodic Condensed Matter Systems

该个人研究者奖支持一个研究项目，重点研究凝聚态物理中非线性纳米级局部化现象和离散模式形成的实验研究。利用特定的大振幅非线性平面波激励的调制不稳定性是在纳米尺度区域内产生这种内在能量局域化的一种方法。为了更好地理解晶体中平面波不稳定性到纳米级能量局域化的途径，将进行三种不同类型的实验：(a)一维微机械阵列中的固有局域模式（ILMs）将使单色能量局域化现象的长时间产生研究成为可能。(b)将研究经典类一维反铁磁晶体的本征局域自旋波模式，试图观察新预测的局域自旋翻转，它代表了比ILM更局域化和更大的能量激发。(c)将利用杰斐逊实验室产生的高强度宽带太赫兹辐射，研究量子反铁磁体和软模式准电晶体的固有纳米级能量局域化。在进行非线性实验与数值模拟相结合的过程中，研究生和本科生都将在这个不断发展的跨学科领域中培养专业知识。非线性和晶格离散性在物理学的许多分支中都起着重要的作用。凝聚态物理的传统方法是分别处理这两个项目。近年来，人们预测并认识到在强非线性离散系统中会出现全新的动力学现象。例如，固体中的大振幅长波振动可以随着振动振幅的大幅增加而迅速级联下来并在原子尺度上定位。由此产生的晶体中离散的纳米尺度图案被预测会产生不同的物理状态。这个实验研究项目探索了这样的新现象。在非线性能量局部化行为方面的科学活动的快速增长表明，这些效应可能在许多领域发挥作用，例如摩擦和裂纹扩展。还有一些发展中的领域涉及更大的长度尺度，如光开关、非线性光子晶体波导、周期性电约瑟夫森结阵列、微机电硅系统，以及在最大尺度上，高能加速器中多束模式的局域化。参与该项目的研究生和本科生将接受涉及技术上重要长度尺度的凝聚态系统的非线性动力学训练。

This individual investigator award supports a research program focused on the experimental investigation of nonlinear nanoscale localization phenomena and discrete pattern formation in condensed matter physics. One way to produce such intrinsic energy localization over a nanoscale region is by making use of the modulational instability of specific large amplitude nonlinear plane wave excitations. To better understand the pathways from plane wave instability to nanoscale energy localization in crystals, three different classes of experiments will be carried out: (a) Intrinsic localized modes (ILMs) in 1D micromechanical arrays will make possible the study of the long time production of monochromatic energy localization phenomena. (b) Intrinsic localized spin wave modes in classical 1D-like antiferromagnetic crystals will be studied in an attempt to observe the newly predicted localized spin flop, which represents a more localized and larger energy excitation than does an ILM. (c) Intrinsic nanoscale energy localization in quantum antiferromagnets and also in soft mode paraelectric crystals will be investigated using high-intensity broadband THz radiation produced at the Jefferson Laboratory. In carrying out nonlinear experiments coupled with numerical simulations both graduate and undergraduate students will develop expertise in this developing interdisciplinary field. Both nonlinearity and lattice discreteness have played important roles in many branches of physics. The traditional approach in condensed matter physics has been to treat these two items separately. Recently it has been predicted and realized that completely new kinds of dynamical phenomena occur in strongly nonlinear discrete systems. For example, large amplitude long wavelength vibrations in a solid can rapidly cascade down and localize at the atomic scale with a large increase in the vibrational amplitude. The resulting discrete nanoscale patterns in the crystal are predicted to give rise to different physical states. This experimental research program explores such new phenomena. The rapid growth of scientific activity in nonlinear energy localization behavior has shown there are a variety of areas where these effects may play a role, such as friction, and crack propagation. Still other developing areas involve somewhat larger length scales such as optical switches, nonlinear photonic crystal waveguides, periodic electrical Josephson junction arrays, micro-electrical-mechanical silicon systems, and, at the largest scale, the localization within multibunch modes in high energy accelerators. Graduate and undergraduate students working on this project will receive training in nonlinear dynamics in condensed matter systems involving technologically important length scales.