Berezinskii-Kosterlitz-Thouless Transition in a Two-dimensional Dipolar Bose Gas

Instead of statistic-driven Bose-Einstein-Condensate transition, interaction-driven Berezinskii-Kosterlitz-Thouless(BKT) transition connects the normal phase and superfluid phase in two dimension(2D) where a quasi long-range order reveals superfluidity. The BKT transition has been extensively studied with ultracold quantum gases in quasi-2D confinement, but only with contact interactions so far. In this talk, we will present the latest study on 2D quantum gases with long-range and anisotropic dipole-dipole interaction (DDI) utilizing magnetic erbium atoms in a quasi-2D harmonic trap. We characterize the dipole-angle-dependent BKT transition point by measuring the onset of extended coherence and equation of states (EoS). We also investigate the scale invariance and universal behavior around the BKT critical point in the presence of DDI. Additionally, we observe a unique anisotropic number fluctuation in the dipolar 2D superfluid with tilted dipoles, which reflects the anisotropic density-density correlation in the system.