The Dynamic Structure Factor of the 1D Bose Gas near the Tonks-Girardeau Limit

TL;DR

This paper calculates the dynamic structure factor of the 1D Bose gas near the Tonks-Girardeau limit, revealing a crossover from non-superfluid to superfluid behavior observable experimentally.

Contribution

It introduces a fermionic pseudopotential approach and derives an analytical RPA expression for the dynamic structure factor near the Tonks-Girardeau limit.

Findings

Identifies a crossover in the dynamic structure factor from non-superfluid to superfluid regimes.

Provides an analytical RPA-based formula valid at first order in 1/γ.

Suggests experimental observability via Bragg scattering.

Abstract

While the 1D Bose gas appears to exhibit superfluid response under certain conditions, it fails the Landau criterion according to the elementary excitation spectrum calculated by Lieb. The apparent riddle is solved by calculating the dynamic structure factor of the Lieb-Liniger 1D Bose gas. A pseudopotential Hamiltonian in the fermionic representation is used to derive a Hartree-Fock operator, which turns out to be well-behaved and local. The Random-Phase approximation for the dynamic structure factor based on this derivation is calculated analytically and is expected to be valid at least up to first order in $1/\gamma$, where $\gamma$ is the dimensionless interaction strength of the model. The dynamic structure factor in this approximation clearly indicates a crossover behavior from the non-superfluid Tonks to the superfluid weakly-interacting regime, which should be observable by Bragg scattering in current experiments.