Localizing Energy Through Nonlinearity and Discreteness
نویسندگان
چکیده
ally perceived as arising from extrinsic disorder that breaks the discrete translational invariance of the perfect crystal lattice. Familiar examples include the localized vibrational phonon modes around impurities or defects (such as atomic vacancies or interstitial atoms) in crystals and Anderson localization of electrons in disordered media.1 The usual perception among solid-state researchers is that, in perfect lattices—those free of extrinsic defects—phonons and electrons exist only in extended, plane wave states. That notion extends to any periodic structure, such as a photonic crystal or a periodic array of optical waveguides. Such firmly entrenched perceptions were severely jolted in the late 1980s by the discovery that intrinsic localized modes2 (ILMs), also known as discrete breathers3 (DBs), are, in fact, typical excitations in perfectly periodic but strongly nonlinear systems. The past several years have seen this prediction confirmed by a flood of experimental observations of ILMs in physical systems ranging from electronic and magnetic solids, through microengineered structures including Josephson junctions and optical waveguide arrays, to laserinduced photonic crystals. Experimentalists are currently hot on the trail of ILMs in Bose–Einstein condensates (BECs) and biopolymers. Hopes are high that these exotic excitations will be useful in all-optical logic and switching devices and in targeted breaking of chemical bonds, and will prove helpful to the understanding of melting processes in solids and conformational changes in biomolecules. In this brief overview, we have attempted to capture the excitement and to explain the essence of these remarkable nonlinear excitations. We urge readers to consult some of the several pioneering papers, recent reviews, and Web sites for more details.2,3
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