2014/09/30 by Wonyoung Cho, Sang-Woo Kim, Jeong-Hyuck Park · 1 citation
Physics and Astronomy · #cond-mat.quant-gas #cond-mat.stat-mech #hep-th
paper · pdf · doi:10.1088/1367-2630/17/1/013038
published as New J. Phys. 17 (2015) 013038 · 17 pages, 4 figures; version expanded, To appear in New Journal of Physics
arxiv created 2014/12/10 · arxiv updated 2015/01/27
Evading the Mermin-Wagner-Hohenberg no-go theorem and revisiting with rigor the ideal Bose gas confined in a square box, we explore a discrete phase transition in two spatial dimensions. Through both analytic and numerical methods we verify that thermodynamic instability emerges if the number of particles is sufficiently yet finitely large: specifically N≥ 35131. The instability implies that the isobar of the gas zigzags on the temperature-volume plane, featuring supercooling and superheating phenomena. The Bose-Einstein condensation then can persist from absolute zero to the superheating temperature. Without necessarily taking the large N limit, under constant pressure condition, the condensation takes place discretely both in the momentum and in the position spaces. Our result is applicable to a harmonic trap. We assert that experimentally observed Bose-Einstein condensations of harmonically trapped atomic gases are a first-order phase transition which involves a discrete change of the density at the center of the trap.