Disorders can induce continuously varying universal scaling in driven systems

We elucidate the nature of universal scaling in a class of quenched disordered driven models. In particular, we explore the intriguing possibility of whether coupling with quenched disorders can lead to continuously varying universality classes. We examine this question in the context of the Kardar-Parisi-Zhang (KPZ) equation, with and without a conservation law, coupled with quenched disorders having distributions with pertinent structures. We show that when the disorder is relevant in the renormalization group sense, the scaling exponents can depend continuously on a dimensionless parameter that defines the disorder distribution. This result is generic and holds for quenched disorders with or without spatially long-ranged correlations, as long as the disorder remains a "relevant perturbation" on the pure system in the renormalization group sense and a dimensionless parameter naturally exists in its distribution. We speculate on its implications for generic driven systems with quenched disorders, and we compare and contrast with the scaling displayed in the presence of annealed disorders.