Ci. Um et al., VARIATIONAL DENSITY-MATRIX APPROACH TO THE TEMPERATURE-DEPENDENT ELEMENTARY EXCITATION SPECTRUM OF 2-DIMENSIONAL LIQUID-HE-4, Journal of low temperature physics, 102(3-4), 1996, pp. 307-324
Using the variational density matrix method, we obtain a temperature-d
ependent elementary excitation spectrum for two-dimensional liquid He-
4. Ebv more precise results, we use a Jastrow-Feenberg-type trial wave
function aad include the contribution of elementary diagrams within t
he hypernetted chain approximation. The behavior of the excitation spe
ctrum as a function of the temperature and density in two dimensions i
s similar to that of the bulk system, but has a smaller roton minimum.
The roton minimum of the excitation spectrum decreases with increasin
g temperature and increases with increasing density at low densities b
ut decreases at large densities. The results agree well with Monte Car
lo calculations and ave closer than pevious theories to experimental m
easurements of He-4 film adsorbed on substrates.