Optical properties of large and small polarons and bipolarons

• Published in: Physical review. B, Condensed matter Vol. 48; no. 18; pp. 13691 - 13702
• Main Author: EMIN, D
• Format: Journal Article
• Language: English
• Published: Woodbury, NY American Physical Society 01-11-1993; American Institute of Physics
• Subjects: 665400 - Quantum Physics Aspects of Condensed Matter- (1992-); ABSORPTION SPECTRA; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Condensed matter: electronic structure, electrical, magnetic, and optical properties; COPPER COMPOUNDS; COUPLING; CUPRATES; Electron states; ELECTRON-PHONON COUPLING; Exact sciences and technology; General theory; HIGH-TC SUPERCONDUCTORS; IONIZATION; MATRIX ELEMENTS; OPTICAL PROPERTIES; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; OXYGEN COMPOUNDS; PHOTOIONIZATION; PHYSICAL PROPERTIES; Physics; POLARONS; Polarons and electron-phonon interactions; QUASI PARTICLES; SPECTRA; SUPERCONDUCTORS; Theory, models, and numerical simulation; TRANSITION ELEMENT COMPOUNDS; Self trapping; Frequency dependence; Energy levels; Charge carriers; Theoretical study; Dimensions; Coulomb field; Free carrier; Line broadening; Electron lattice interaction; Photoionization; Bipolaron; Transport processes; Absorption spectra; Matrix elements; Polarons
• ISSN: 0163-1829; 1095-3795
• DOI: 10.1103/physrevb.48.13691

In systems that are two and three dimensional electronically, a large polaron and a small polaron are distinct types of quasiparticles. The type of polaron formed depends on which electron-lattice interaction is of primary importance. A large polaron forms when the electron-lattice interaction due to the long-range Coulombic interactions between an electronic carrier and a solid's ions are of paramount importance. Competing effects then determine the radius of a large polaron. By contrast, a small polaron can form when a short-range electron-lattice interaction, such as the deformation-potential interaction, is dominant. A small polaron forms as its self-trapped carrier shrinks without limit until it is confined to a single site. Fundamental differences between large and small polarons produce optical spectra with distinguishing features. The absorption due to photoionization of a large polaron depends on products of the matrix elements for exciting a carrier from its self-trapped states to a free-carrier state and the density of these free-carrier states. These matrix elements fall sharply with increasing free-carrier wave vector [ital k] when [ital kR][gt]1, where [ital R] is the large polaron's radius. A large polaron's photoionization produces a temperature-independent absorption band. This band is asymmetric with the absorption intensity on the high-energy side of the peak exceeding that on the low-energy side of the peak.