Flux-flow fingerprint of disorder: Melting versus tearing of a flux-line lattice

A steady-state inhomogeneous flow of a slowly moving flux-line lattice shows the fingerprint of the specific realization of dynamically generated disorder obtained through the interaction between the lattice and the quenched pinning centers. This is characteristic of ``tearing'' of a soft lattice and is pronounced in a narrow regime of the (H,T) phase diagram where the system is neither a stiff lattice nor a fluid. A first-order depinning transition accompanying this nonequilibrium dynamical phenomenon is fundamentally different from an equilibrium ``melting'' of a flux-line lattice. A length scale is proposed to describe the dynamics.