Local and global heat capacities of confined Bose gases: The impact of quantum migration.

The recently proposed macroscopic quantum phenomenon, Temperature-Induced Quantum Migration (TIQM), causes local heating and cooling and significantly affects the local heat capacity of a noninteracting confined Maxwell-Boltzmann gas. TIQM guarantees the non-negativity of local heat capacity at low temperatures, results in a substantial local heat-capacity overshoot, and provides a physical basis for global heat-capacity maxima and thermal confinement energy. We extend this framework here to Bose gases in three different rectangular domains, effectively providing three-dimensional (3D)/two-dimensional (2D)/one-dimensional (1D) confinement at high temperatures while transitioning to 2D/1D/zero-dimensional (0D) at low temperatures, thus inducing dimensional crossovers during temperature changes. We demonstrate that quantum degeneracy enhances the TIQM process, resulting in dimension-dependent effects on local and global heat capacities. For the 3D-2D crossover, TIQM leads to a giant excess local heat capacity and explains the mechanism for the enhancement of the global heat-capacity maximum, which surpasses the unconfined ideal Bose gas limit (1.93), reaching 1.97 at a finite density. Conversely, for the 2D-1D and 1D-0D crossovers, the excess local heat capacity diminishes with increasing quantum degeneracy (density), while it is TIQM alone that becomes responsible for excess global heat capacity. For the 1D-0D crossover, we find that only single-particle ergodic systems can have a global excess heat capacity; otherwise, the maximum behavior disappears completely. TIQM also provides a mechanism for the thermal confinement energy in Bose gases.