Effect of spin-density waves on the lattice dynamics of metals
Abstract
Spin density waves (SDW's) have built-in charge modulations, equal in magnitude but opposite in sign, for both spin states. A small shift in the spatial phase $\delta\phi$ = $\epsilon\sigma\sb{z}$, depending on the spin $\sigma\sb{z}$, creates an additional charge response, and causes a peak in the response function $Q(\vec q)$ for $\vec q$ near $\pm\vec Q$, where $\vec Q$ is the SDW wave vector. When this spin-split-phase contribution to $Q(\vec q)$ is incorporated into the theory for phonon spectra of metals, several anomalous behaviors can be understood, including the large depressions in both longitudinal and transverse modes at the zone-boundary in lead and the frequency softening of the (001) LO branch at the zone-center in zirconium. The large anisotropy in the magnetic susceptibility of Zr can also be attributed to the anisotropic spin paramagnetism of an SDW state. The shell model of lattice dynamics is used to study the reduction of the Coulomb repulsion caused by the collective oscillations of the last-filled negative-ion shells in transition-metal oxides and sulfides. The screening energy of two electrons on the same metal-site minus their sum when separated is found to be $\Delta U \cong -10eV$. It follows that the on-site Coulomb interaction parameter U in the Hubbard model is reduced from a large $U\sb{bare}$ to a small net value.
Degree
Ph.D.
Advisors
Overhauser, Purdue University.
Subject Area
Condensation
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.