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

Conference · Sat Jan 01 00:00:00 EST 1977

OSTI ID:5085513

Das, S G; Sinha, S K; Wakabayashi, N

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/.

• Research Organization: Argonne National Lab., Ill. (USA); Oak Ridge National Lab., Tenn. (USA)
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 5085513
• Report Number(s): CONF-770913-8; TRN: 78-010410
• Resource Relation: Conference: International conference on lattice dynamics, Paris, France, 5 Sep 1977
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
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CRYSTAL LATTICES
INSTABILITY
CHALCOGENIDES
CRYSTAL STRUCTURE
NIOBIUM COMPOUNDS
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SELENIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
656000* - Condensed Matter Physics
360104 - Metals & Alloys- Physical Properties