First and second sound in a dilute Bose gas across the BKT transition

authored by: Vijay Pal Singh, Ludwig Mathey
Abstract: We study the propagation of the two sound modes in two-dimensional Bose gases across the Berezinksii-Kosterlitz-Thouless transition using classical-field dynamics, which is motivated by recent measurements of Christodoulou et al (2021 Nature 594 191). Based on the dynamic structure factor (DSF), we identify the two sound modes as the Bogoliubov (B) and the non-Bogoliubov (NB) sound mode below the transition, and as the diffusive and the normal sound mode above the transition. The NB sound mode velocity is higher than the B sound mode velocity, which we refer to as the weak-coupling regime of the sound modes. We excite the sound modes by driving the system as in the experiment and by perturbing the density with a step-pulse perturbation, as a secondary comparison. The driven response depends on the driving strength and results in higher velocities for the B sound mode at high temperatures near the transition, compared to the sound results of the DSF and step-pulse excitation. We show that the higher mode velocity has a weak temperature dependence across the transition, which is consistent with the experimental observation.
Organisation(s): Institute of Theoretical Physics
QuantumFrontiers
External Organisation(s): Universität Hamburg
Type: Article
Journal: New journal of physics
Volume: 24
No. of pages: 10
ISSN: 1367-2630
Publication date: 01.07.2022
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Physics and Astronomy(all)
Electronic version(s): https://doi.org/10.48550/arXiv.2203.08837 (Access: Open)
https://doi.org/10.1088/1367-2630/ac7d6f (Access: Open)

BibTeX

@article{d58761438d2149899d29c0ac7ac33215,
title = "First and second sound in a dilute Bose gas across the BKT transition",
abstract = "We study the propagation of the two sound modes in two-dimensional Bose gases across the Berezinksii-Kosterlitz-Thouless transition using classical-field dynamics, which is motivated by recent measurements of Christodoulou et al (2021 Nature 594 191). Based on the dynamic structure factor (DSF), we identify the two sound modes as the Bogoliubov (B) and the non-Bogoliubov (NB) sound mode below the transition, and as the diffusive and the normal sound mode above the transition. The NB sound mode velocity is higher than the B sound mode velocity, which we refer to as the weak-coupling regime of the sound modes. We excite the sound modes by driving the system as in the experiment and by perturbing the density with a step-pulse perturbation, as a secondary comparison. The driven response depends on the driving strength and results in higher velocities for the B sound mode at high temperatures near the transition, compared to the sound results of the DSF and step-pulse excitation. We show that the higher mode velocity has a weak temperature dependence across the transition, which is consistent with the experimental observation.",
keywords = "Berezinksii-Kosterlitz-Thouless transition, collective modes, first and second sound, ultracold atom superfluids",
author = "Singh, {Vijay Pal} and Ludwig Mathey",
note = "Funding Information: We thank Panagiotis Christodoulou for insightful discussions. This work is supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of SFB 925—Project ID 170620586 and the excellence cluster {\textquoteleft}Advanced Imaging of Matter{\textquoteright}—EXC 2056—Project ID 390715994, and the Cluster of Excellence {\textquoteleft}QuantumFrontiers{\textquoteright}—EXC 2123—Project ID 390837967. ",
year = "2022",
month = jul,
day = "1",
doi = "10.48550/arXiv.2203.08837",
language = "English",
volume = "24",
journal = "New journal of physics",
issn = "1367-2630",
publisher = "IOP Publishing Ltd.",
number = "7",
}