Physical review. B, Solid state
Analytical structure of the wave-number-dependent susceptibility of many-fermion systems at low temperature and long wavelength
D. J. W. Geldart, Mark Rasolt
Abstract
The analytical structure of the wave-number-dependent magnetic susceptibility $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ is studied at small wave number $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ and low temperature. It is found to exhibit a nonanalytic behavior in contrast to commonly assumed forms for $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ of interacting systems. The importance and implications of these results are discussed for the cases of short-range point interactions and long-range Coulomb interactions.