Dynamical Structure Factors in Quantum Many-Body Systems from Quantum Monte Carlo Calculations

TL;DR

This paper introduces a new ab-initio method combining integral transforms and Quantum Monte Carlo to accurately compute dynamical structure factors in quantum many-body systems, demonstrated on bulk helium-4.

Contribution

It develops a novel, model-independent approach to determine dynamical structure functions using Quantum Monte Carlo and integral transforms, applied to helium-4.

Findings

Predicted position and width of collective excitations in helium-4

Computed incoherent excitation spectrum across momentum ranges

Accurately characterized collective modes in the maxon-roton region

Abstract

An ab-initio method for determining the dynamical structure function of an interacting many--body quantum system has been devised by combining a generalized integral transform method with Quantum Monte Carlo methods. As a first application, the coherent and, separately, the incoherent excitation spectrum of bulk atomic 4He has been computed, both in the low and intermediate momentum range. The peculiar form of the kernel in the integral transform of the dynamical structure function allows to predict, without using any model, both position and width of the collective excitations in the maxon--roton region, as well as the second collective peak. A prediction of the dispersion of the single--particle modes described by the incoherent part is also presented.