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On the crossing of dispersion curves of alkali metals in [ζ00] direction
Author(s) -
Ramamurthy V.,
Singh K. K.
Publication year - 1978
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220850241
Subject(s) - degeneracy (biology) , condensed matter physics , alkali metal , lattice (music) , electron , lattice vibration , dispersion (optics) , physics , boundary value problem , wave vector , lithium (medication) , phonon , quantum mechanics , medicine , endocrinology , acoustics , bioinformatics , biology
The experimentally observed dispersion curves of lithium, sodium, and potassium in [ζ00] direction, especially the degeneracy of the zone boundary frequencies and the anomalous crossing in lithium, are reproduced completely by a lattice dynamical which model which takes into account the umklapp processes and the screening associated with the electrons. It is shown that the observed crossing in lithium is associated with the large positive value of the bulk modulus of the electron gas, together with the variation of umklapp contribution to these modes of vibration with the wave vector. The latter leads to the observed degeneracy at the zone boundary point. The role played by umklapp processes in producing effects is discussed.