Description:

Abstract: Topological defects provide symmetry breaking in systems with longrang order. Examples in condensed matter are domain walls and spinskyrmions in magnetic materials, edge and screw dislocations incrystals, vortices in superconductors and superfluids, textures inliquid crystals. Once created, the topologically protected defectscan only disappear by exiting through the surface or annihilatingwith defects of opposite polarity. Proliferation of topologicaldefects like vortices and dislocations can break the globallong-range order in superconductivity and superfluidity in thin filmsand enable plasticity of solids and melting of atomic monolayers. Forinstance, breaking the global phase coherence in superfluid orsuperconducting films can occur via theBerezinskii-Kosterlitz-Thouless unbinding of vortex-antivortex pairsin thermodynamic equilibrium. An open question is whether atopological defect can be destroyed by a strong force. In this talk Iwill show that applying a strong driving force to a vortex inJosephson junctions, 2D Josephson junction arrays or layered high-Tcsuperconductors can trigger a chain reaction of self-replicatingexpanding vortex-antivortex pairs forming branching multiquantadynamic patterns. This process can be described in terms ofpropagating phase cracks in long-range order, similar to the pileupof dislocations at the initial stage of crack expansion in crystals.In a nonequilibrium state the global long-range order can thus bedestroyed by proliferation of topological defects initiated by asingle driven topological defect. I will present results of ourrecent numerical simulations of a Josephson vortex trapped in alayered high-Tc cuprates and driven by a dc current flowing along thec-axis. Such Josephson vortex gets periodically reflected from thesample edges and behaves like a magnetic flux shuttle which startsgenerating vortex-antivortex pairs above a threshold current. Theresulting bouncing macrovortices get synchronized, causinglarge-amplitude standing electromagnetic waves and oscillatingmagnetic moment of phase-locked CuO planes, which can producecoherent THz radiation from the cuprate BSCCO mesas. 

Speaker: Alex Gurevich, Professor and Eminent Scholar, Old Dominion University 

Host: Professor James Sauls