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

Conference · Wed Feb 01 04:00:00 EST 1978

OSTI ID:5150126

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/, we have assumed 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. 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 atom 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, we have 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-7405-ENG-26
• OSTI ID: 5150126
• Report Number(s): CONF-7709106-1
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
656000 -- Condensed Matter Physics
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BAND THEORY
CHALCOGENIDES
CHARGE DENSITY
COHERENT SCATTERING
DIFFRACTION
INSTABILITY
LATTICE PARAMETERS
LCAO METHOD
NEUTRON DIFFRACTION
NIOBIUM COMPOUNDS
NIOBIUM SELENIDES
RELAXATION
SCATTERING
SELENIDES
SELENIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
WAVE PROPAGATION