Kinetic decoupling in electron-beam-driven dusty plasma: Microscopic randomization coexisting with collective flow stability.

Abstract

Energy injection and dissipation in nonequilibrium systems typically lock microscopic motion and collective flow into a coupled evolution. Our observations in electron-beam-driven dusty plasma reveal a distinct "kinetic decoupling" regime where this synchrony breaks down. While microscopic and collective entropies evolve in tandem at low energies, a sharp "entropic scissors" effect emerges at a critical threshold: microscopic velocity randomization reaches a maximum, while collective flow fluctuations are simultaneously suppressed. The resulting state behaves as an ergodic, thermal-like fluid where intense local mixing coexists with global transport stability. This phenomenology originates from a fundamental timescale separation between rapid energy injection and slower neutral-drag dissipation, sustaining microscopic randomization while quenching large-scale instabilities. The dual-entropy framework introduced here provides a model-independent diagnostic for emergent scale separation, applicable to diverse driven many-body platforms.