ESPCI web site
Thursday September 19 at 11:00 am (Paris time)
ESPCI, Room Holweck, Building C, 1st Floor
What can happen if a topological defect is broken by a strong driving force ?
Topological defects provide symmetry breaking in systems with long rang order. Examples are domain walls and spin skyrmions in magnetic materials, edge and screw dislocations in crystals, vortices in superconductors and superfluids, textures in liquid crystals. Once created, the topologically protected defects can only disappear by exiting through the surface or annihilating with defects of opposite polarity. Proliferation of topological defects like vortices and dislocations can break the global long-range order in superconductivity and superfluidity in thin films and enable plasticity of solids and melting of atomic monolayers. For instance, breaking the global phase coherence in superfluid or superconducting films can occur via the Berezinskii-Kosterlitz-Thouless unbinding of vortex-antivortex pairs in thermodynamic equilibrium. An open question is whether a topological defect can be destroyed by a strong force. In this talk I will show that applying a strong driving force to a vortex in Josephson junctions, 2D Josephson junction arrays or layered high-Tc superconductors can trigger a chain reaction of self-replicating expanding vortex-antivortex pairs forming branching multiquanta dynamic patterns. This process can be described in terms of propagating phase cracks in long-range order, similar to the pileup of dislocations at the initial stage of crack expansion in crystals. In a nonequilibrium state the global long-range order can thus be destroyed by proliferation of topological defects initiated by a single driven topological defect. I will present results of our recent numerical simulations of a Josephson vortex trapped in a layered high-Tc cuprates and driven by a dc current flowing along the c-axis. Such Josephson vortex gets periodically reflected from the sample edges and behaves like a magnetic flux shuttle which stimulates generation of vortex-antivortex pairs above a threshold current. The resulting bouncing macrovortices get synchronized, exciting large-amplitude electromagnetic resonant modes and oscillating magnetic moment of phase-locked CuO planes, which can produce coherent THz radiation from the cuprate BSCCO mesas.
