Sato M, Sievers A J
Laboratory of Atomic and Solid State Physics and Cornell Center for Materials Research, Cornell University, Ithaca, New York 14850-2501, USA.
Nature. 2004 Nov 25;432(7016):486-8. doi: 10.1038/nature03038.
In a strongly nonlinear discrete system, the spatial size of an excitation can become comparable to, and influenced by, the lattice spacing. Such intrinsic localized modes (ILMs)--also called 'discrete breathers' or 'lattice solitons'--are responsible for energy localization in the dynamics of discrete nonlinear lattices. Their energy profiles resemble those of localized modes of defects in a harmonic lattice but, like solitons, they can move (although, unlike solitons, some energy is exchanged during collisions between them). The manipulation of these localized energy 'hotspots' has been achieved in systems as diverse as annular arrays of coupled Josephson junctions, optical waveguide arrays, two-dimensional nonlinear photonic crystals and micromechanical cantilever arrays. There is also some evidence for the existence of localized excitations in atomic lattices, although individual ILMs have yet to be identified. Here we report the observation of countable localized excitations in an antiferromagnetic spin lattice by means of a nonlinear spectroscopic technique. This detection capability permits the properties of individual ILMs to be probed; the disappearance of each ILM registers as a step in the time-dependent signal, with the surprising result that the energy staircase of ILM excitations is uniquely defined.
在一个强非线性离散系统中，激发的空间尺寸会变得与晶格间距相当，并受其影响。这种本征局域模（ILMs）——也被称为“离散呼吸子”或“晶格孤子”——是离散非线性晶格动力学中能量局域化的原因。它们的能量分布类似于简谐晶格中缺陷的局域模，但与孤子一样，它们可以移动（不过，与孤子不同的是，它们之间碰撞时会交换一些能量）。在诸如耦合约瑟夫森结环形阵列、光波导阵列、二维非线性光子晶体和微机械悬臂阵列等多种系统中，已经实现了对这些局域能量“热点”的操控。虽然尚未识别出单个的本征局域模，但也有一些证据表明原子晶格中存在局域激发。在此，我们报告通过非线性光谱技术在反铁磁自旋晶格中观测到可数的局域激发。这种探测能力使得能够探究单个本征局域模的性质；每个本征局域模的消失在随时间变化的信号中表现为一个台阶，令人惊讶的是，本征局域模激发的能量阶梯是唯一确定的。
