凝聚態(tài)光物理學(xué)ppt課件-資料下載頁(yè)
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【正文】 stal. Bloch’s theorem states that the wave functions: where uk(r ) is a function that has the periodicity of the lattice. Each electronic band has a different envelope function uk(r ) Vibronic bands The band arises from the coupling of discrete electronic state to a continuous spectrum of vibrational mode. This contrast with the electronic band that arises from interaction between electronic states of neighbouring atoms. The density of states This is defined as: Number of states in the range E ? ( E + d E) = g (E) d E. g(E) is work out in practice: g(E) = g(k)dk / dE This can be evaluated from knowledge of the Ek relationship for electrons or phonons. Delocalized states and collective excitations phonon: the collective excitation of lattice vibration。 exciton: formed from delocalized electrons and holes in semiconductors。 plasmon: formed from free electrons in metals and doped semiconductors。 … … many optical effects related to these … … Microscopic models Classical : Treat both the medium and the light according to classical physics。 Semiclassical: apply quantum mechanics to atoms, treat light as a classical electromagic wave。 Fully quantum: both atoms and light are treated quantum mechanically. Characteristic optical physics in the condensed matter Exercises: 1. The plex refractive index of germanium at 400 nm is given by . Calculate for germanium at 400 nm: (a) the phase velocity of light, (b) the absorption coefficient, and ( c) the reflectivity. 2. Show that the optical density (.) of a sample is related to its transmission T and reflectively R through: Hence explain how you would determine the optical density by making two transmission measurements, one at wavelength ? where the material absorbs, and the other at a wavelength ?’ where the material is transparent. ~ in ??).1(l o g2)(l o g.. 1010 RTDO ????
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