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Unformatted text preview: Solid State Theory Exercise 4 SS 11 Prof. M. Sigrist Excitons Exercise 4.1 OneDimensional Model of a Semiconductor Let us consider electrons moving on a onedimensional chain. We use the socalled tight binding approximation. Thus, we assume that each atom has a localized electron state and that the electrons are able to hop between neighboring atoms. This hopping process describes the kinetic energy term. It is most convenient to use a secondquantized language. For simplicity, we assume spinless electrons. Let c i and c † i be the creation and annihilation operators for an electron at site i , respectively. The overlap integral between neighboring electron states is denoted by t . Then, the kinetic energy operator is written as H = t X i c † i c i +1 + c † i +1 c i . (1) We assume that the chain contains N atoms and in the following we set the lattice constant a = 1. Furthermore, we assume that two consecutive atoms are nonequivalent which is modeled by an alternating potential of the form V = v X i ( 1) i c † i c i . (2) [a] Consider first the case...
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This note was uploaded on 10/04/2011 for the course PHYS fs11 taught by Professor Sigrist during the Spring '11 term at Swiss Federal Institute of Technology Zurich.
 Spring '11
 Sigrist

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