Dynamic properties and the roton mode attenuation in liquid 3 He: ab initio study within the self-consistent method of moments

Abstract

The dynamic structure factor and the eigenmodes of density fluctuations in liquid 3 He are studied using a novel non-perturbative approach. This new version of the self-consistent method of moments invokes up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo simulations which provide necessary reliable input information on the system static properties. Detailed analysis is performed of the collective excitations dispersion relations, the modes’ decrements and the static structure factor of 3 He at the saturated vapour pressure. The results are compared to available experimental data by Albergamo et al. (Albergamo et al. 2007 Phys. Rev. Lett. 99 , 205301. ( doi:10.1103/PhysRevLett.99.205301 )) and Fåk et al. (Fåk et al. 1994 J. Low Temp. Phys. 97 , 445–487. ( doi:10.1007/BF00754303 )). The theory reveals a clear signature of the roton-like feature in the particle-hole segment of the excitation spectrum with a significant reduction of the roton decrement in the wavenumber range 1.3   Å − 1 ≤ q ≤ 2.2   Å − 1 . The observed roton mode remains a well-defined collective mode even in the particle-hole band, where it is strongly damped. The existence of the roton-like mode in the bulk liquid 3 He is confirmed like in other quantum fluids. The phonon branch of the spectrum is in a reasonable agreement with the same experimental data. This article is part of the theme issue ‘Dynamic and transient processes in warm dense matter’.