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

Abstract

Universal scaling behavior in the relaxation dynamics of an isolated\ntwo-dimensional Bose gas is studied by means of semi-classical stochastic\nsimulations of the Gross-Pitaevskii model. The system is quenched far out of\nequilibrium by imprinting vortex defects into an otherwise phase-coherent\ncondensate. A strongly anomalous non-thermal fixed point is identified,\nassociated with a slowed decay of the defects in the case that the dissipative\ncoupling to the thermal background noise is suppressed. At this fixed point, a\nlarge anomalous exponent $\\eta \\simeq -3$ and, related to this, a large\ndynamical exponent $z \\simeq 5$ are identified. The corresponding power-law\ndecay is found to be consistent with three-vortex-collision induced loss. The\narticle discusses these aspects of non-thermal fixed points in the context of\nphase-ordering kinetics and coarsening dynamics, thus relating phenomenological\nand analytical approaches to classifying far-from-equilibrium scaling dynamics\nwith each other. In particular, a close connection between the anomalous\nscaling exponent $\\eta$, introduced in a quantum-field theoretic approach, and\nconservation-law induced scaling in classical phase-ordering kinetics is\nrevealed. Moreover, the relation to superfluid turbulence as well as to driven\nstationary systems is discussed.\n