Exchange and Correlation Instabilities of Simple Metals

TLDR

Screened interactions inadequately treat exchange instabilities; the wave vector adjusts to align the Fermi surface with energy gaps, optimizing correlation energy and suggesting charge‑density‑wave ground states in simple metals with weak ion‑ion interactions. The study examines how electron‑electron correlation influences exchange instabilities in metals. The authors compute the intensity of Bragg‑reflection satellites arising from a concomitant positive‑ion modulation. Correlation suppresses ferromagnetic instabilities but enhances charge‑density‑wave exchange instabilities, as shown by the alignment of long‑period superlattice periodicity with the Fermi surface in order‑disorder alloys.

Abstract

The influence of electron-electron correlation on exchange instabilities of a metal is examined. The employment of screened interactions does not constitute a proper treatment. Correlation effects suppress ferromagnetic instabilities, as is well known, but they need not supress instabilities of the spin-density-wave type. On the contrary, it is shown that correlation enhances exchange instability of the charge-density-wave type. For either type, the wave vector of such a state adjusts so that the Fermi surface makes critical contact with the energy gaps introduced by the instability. This circumstance optimizes the correlation energy. The observed conjunction of the long-period-superlattice periodicity with the Fermi surface in order-disorder alloys is probably an example of this phenomenon. It is suggested that charge-density-wave ground states are likely in simple metals having weak Born-Mayer ion-ion interactions, such as the alkali metals. The intensity of Bragg reflection satellites caused by a concomitant positive-ion modulation is computed.