Strongly anomalous non-thermal fixed point in a quenched two-dimensional Bose gas

Abstract

Universal scaling behavior in the relaxation dynamics of an isolated two-dimensional Bose gas is studied bymeans of semi-classical stochastic simulations of theGrossPitaevskiimodel. The systemis quenched far out of equilibriumby imprinting vortex defects into an otherwise phase-coherent condensate.A strongly anomalous non-thermal fixed point is identified, associatedwith a slowed decay of the defects in the case that the dissipative coupling to the thermal background noise is suppressed.At this fixed point, a large anomalous exponent η ≃ -3 and, related to this, a large dynamical exponent z ≃ 5 are identified. The corresponding power-lawdecay is found to be consistent with three-vortex-collision induced loss. The article discusses these aspects of non-thermal fixed points in the context of phaseordering kinetics and coarsening dynamics, thus relating phenomenological and analytical approaches to classifying far-from-equilibriumscaling dynamics with each other. In particular, a close connection between the anomalous scaling exponent η, introduced in a quantum-field theoretic approach, and conservation-law induced scaling in classical phase-ordering kinetics is revealed.Moreover, the relation to superfluid turbulence aswell as to driven stationary systems is discussed.