TY - JOUR

T1 - First and second sound in a dilute Bose gas across the BKT transition

AU - Singh, Vijay Pal

AU - Mathey, Ludwig

N1 - 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 ‘Advanced Imaging of Matter’—EXC 2056—Project ID 390715994, and the Cluster of Excellence ‘QuantumFrontiers’—EXC 2123—Project ID 390837967.

PY - 2022/7/1

Y1 - 2022/7/1

N2 - 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.

AB - 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.

KW - Berezinksii-Kosterlitz-Thouless transition

KW - collective modes

KW - first and second sound

KW - ultracold atom superfluids

UR - http://www.scopus.com/inward/record.url?scp=85136592602&partnerID=8YFLogxK

U2 - 10.48550/arXiv.2203.08837

DO - 10.48550/arXiv.2203.08837

M3 - Article

AN - SCOPUS:85136592602

VL - 24

JO - New journal of physics

JF - New journal of physics

SN - 1367-2630

IS - 7

M1 - 073024

ER -