Microscopic theory of charges density wave instability in NbSe/sub 2/

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The microscopic theory of Sinha and Harmon for electronically driven lattice instabilities is used to explain the ''Kohn-like'' anomalies in the ..sigma../sub 1/ phonon branch and the observed incommensurate superlattice Bragg peak in 2H-NbSe/sub 2/, characteristic of the charge density wave at low temperatures in the neutron scattering experiments of Moncton et al. In accordance with the APW and LCAO band-structure calculations of Mattheiss of 2H-NbSe/sub 2/, the presence of three narrow d bands of atomic symmetry xy, x/sup 2/-y/sup 2/ and 3z/sup 2/-r/sup 2/ at the Fermi level is assumed. Thus the conduction-band wave function is represented by a ... continued below

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Pages: 14

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Das, S G; Sinha, S K & Wakabayashi, N January 1, 1977.

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The microscopic theory of Sinha and Harmon for electronically driven lattice instabilities is used to explain the ''Kohn-like'' anomalies in the ..sigma../sub 1/ phonon branch and the observed incommensurate superlattice Bragg peak in 2H-NbSe/sub 2/, characteristic of the charge density wave at low temperatures in the neutron scattering experiments of Moncton et al. In accordance with the APW and LCAO band-structure calculations of Mattheiss of 2H-NbSe/sub 2/, the presence of three narrow d bands of atomic symmetry xy, x/sup 2/-y/sup 2/ and 3z/sup 2/-r/sup 2/ at the Fermi level is assumed. Thus the conduction-band wave function is represented by a linear combination of tight-binding Gaussian atomic orbitals with neglect of the variation of the radial wave function across the bands. The screened electron-ion interaction and the Coulomb energy of the charge fluctuation on the d shells of Nb atoms is represented by a pseudopotential screened by the Lindhard dielectric function. The phonon eigenvectors needed for estimating the electron-phonon interaction were calculated using a simple force constant model. In agreement with the experimental results, it was found that the phonon frequencies for the ..sigma../sub 1/ and ..sigma../sub 3/ branches are very strongly renormalized as one approaches the zone boundary. By introducing the electronic relaxation effects a central peak appears at the q vector of the instability and the actual phonon renormalization is partially suppressed. This explains the superlattice Bragg peaks observed at low temperatures and ''Kohn-like'' anomalies in the ..sigma../sub 1/ phonon branch of NbSe/sub 2/.

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Pages: 14

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Dep. NTIS, PC A02/MF A01.

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  • International conference on lattice dynamics, Paris, France, 5 Sep 1977

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  • Report No.: CONF-770913-8
  • Grant Number: W-31-109-ENG-38
  • Office of Scientific & Technical Information Report Number: 5085513
  • Archival Resource Key: ark:/67531/metadc1058876

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  • January 1, 1977

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  • Jan. 22, 2018, 7:23 a.m.

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  • Feb. 1, 2018, 6:42 p.m.

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Das, S G; Sinha, S K & Wakabayashi, N. Microscopic theory of charges density wave instability in NbSe/sub 2/, article, January 1, 1977; Illinois. (digital.library.unt.edu/ark:/67531/metadc1058876/: accessed April 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.