Universal scaling at nonthermal fixed points of a two-component Bose gas

Quasistationary far-from-equilibrium critical states of a two-component Bose gas are studied in two spatial dimensions. After the system has undergone an initial dynamical instability it approaches a nonthermal fixed point. At this critical point the structure of the gas is characterized by ensembles of (quasi) topological defects such as vortices, skyrmions, and solitons which give rise to universal power-law behavior of momentum correlation functions. The resulting power-law spectra can be interpreted in terms of strong-wave-turbulence cascades driven by particle transport into long-wavelength excitations. Scaling exponents are determined on both sides of the miscible-immiscible transition controlled by the ratio of the intraspecies to interspecies couplings. Making use of quantum turbulence methods, we explain the specific values of the exponents from the presence of transient (quasi)topological defects.