article published yes Luca Salasnich author Alberto Cappellaro author 9d13b3cb-30a2-11eb-80dc-f772505e86600000-0001-6110-2359 Koichiro Furutani author Andrea Tononi author Giacomo Bighin author 4CA96FD4-F248-11E8-B48F-1D18A9856A870000-0001-8823-9777 MiLe department We review our theoretical results of the sound propagation in two-dimensional (2D) systems of ultracold fermionic and bosonic atoms. In the superfluid phase, characterized by the spontaneous symmetry breaking of the U(1) symmetry, there is the coexistence of first and second sound. In the case of weakly-interacting repulsive bosons, we model the recent measurements of the sound velocities of 39K atoms in 2D obtained in the weakly-interacting regime and around the Berezinskii–Kosterlitz–Thouless (BKT) superfluid-to-normal transition temperature. In particular, we perform a quite accurate computation of the superfluid density and show that it is reasonably consistent with the experimental results. For superfluid attractive fermions, we calculate the first and second sound velocities across the whole BCS-BEC crossover. In the low-temperature regime, we reproduce the recent measurements of first-sound speed with 6Li atoms. We also predict that there is mixing between sound modes only in the finite-temperature BEC regime. https://research-explorer.ista.ac.at/download/12154/12361/2022_Symmetry_Salsnich.pdf application/pdfno https://creativecommons.org/licenses/by/4.0/ MDPI2022 eng Physics and Astronomy (miscellaneous)General MathematicsChemistry (miscellaneous)Computer Science (miscellaneous) 2073-8994 00087503920000110.3390/sym14102182 1410 Salasnich, L., Cappellaro, A., Furutani, K., Tononi, A., &#38; Bighin, G. (2022). First and second sound in two-dimensional bosonic and fermionic superfluids. <i>Symmetry</i>. MDPI. <a href="https://doi.org/10.3390/sym14102182">https://doi.org/10.3390/sym14102182</a> Salasnich, Luca, Alberto Cappellaro, Koichiro Furutani, Andrea Tononi, and Giacomo Bighin. “First and Second Sound in Two-Dimensional Bosonic and Fermionic Superfluids.” <i>Symmetry</i>. MDPI, 2022. <a href="https://doi.org/10.3390/sym14102182">https://doi.org/10.3390/sym14102182</a>. Salasnich L, Cappellaro A, Furutani K, Tononi A, Bighin G. First and second sound in two-dimensional bosonic and fermionic superfluids. <i>Symmetry</i>. 2022;14(10). doi:<a href="https://doi.org/10.3390/sym14102182">10.3390/sym14102182</a> L. Salasnich, A. Cappellaro, K. Furutani, A. Tononi, and G. Bighin, “First and second sound in two-dimensional bosonic and fermionic superfluids,” <i>Symmetry</i>, vol. 14, no. 10. MDPI, 2022. Salasnich L, Cappellaro A, Furutani K, Tononi A, Bighin G. 2022. First and second sound in two-dimensional bosonic and fermionic superfluids. Symmetry. 14(10), 2182. Salasnich, Luca, et al. “First and Second Sound in Two-Dimensional Bosonic and Fermionic Superfluids.” <i>Symmetry</i>, vol. 14, no. 10, 2182, MDPI, 2022, doi:<a href="https://doi.org/10.3390/sym14102182">10.3390/sym14102182</a>. L. Salasnich, A. Cappellaro, K. Furutani, A. Tononi, G. Bighin, Symmetry 14 (2022). 121542023-01-12T12:08:31Z2023-08-09T10:13:17Z