• Two-phonon bound states in imperfect crystals

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    • Keywords


      Two-phonon bound states; imperfect crystals; anharmonic crystals; phonon-phonon interactions; combination modes

    • Abstract


      The question of the occurrence of two-phonon bound states in imperfect crystals is investigated. It is shown that the anharmonicity mediated two-phonon bound state which is present in perfect crystals gets modified due to the presence of impurities. Moreover, the possibility of the occurrence of a purely impurity mediated two-phonon bound state is demonstrated. The bound state frequencies are calculated using the simple Einstein oscillator model for the host phonons. The two-phonon density of states for the imperfect crystal thus obtained has peaks at the combination and difference frequencies of two host phonons besides the peaks at the bound state frequencies. For a perfect crystal the theory predicts a single peak at the two-phonon bound state frequency in conformity with experimental observations and other theoretical calculations. Experimental data on the two-phonon infrared absorption and Raman scattering from mixed crystals of GA1−c Alc P and Ge1−c Sic are analysed to provide evidence in support of impurity-mediated two-phonon bound states. The relevance of the zero frequency (difference spectrum) peak to the central peak observed in structural phase transitions, is conjectured;

    • Author Affiliations


      S N Behera1 Sk Samsur1

      1. Institute of Physics, A/105 Saheed Nagar, Bhubaneswar - 751 007, India
    • Dates

  • Pramana – Journal of Physics | News

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      Posted on July 25, 2019

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