Speaker: Liang Luo

Beijing Computational Science Research Center    

Abstract: The two-dimensional gauge glass model has been proposed to study transport properties of granular superconducting films and disordered Josephson-junction arrays in a magnetic field. Detailed analytical and numerical studies have shown that the low temperature equilibrium behavior of the system is controlled by a T=0 critical point with a finite density of states for gapless vortex excitations.However, due to the random potential created by the disorder and the ground state vortex configuration, vortex transport under a weak external current I is expected to be complex and has not been analyzed in detail. In fact, previous numerical work suggested a change of behavior from Ohmic to power-law I-V at around T/J~ 0.22, where J is the Josephson coupling constant between neighboring superconducting grains. We report here more extensive simulations of the gauge glass model under the resistively-shunted-junction (RSJ) dynamics at weak applied currents and lower temperatures. Ohmic behavior is observed down to T=0.1 for arrays of size up to 512x128. Simulations also indicate that the vortex configuration is insensitive to the temperature and a weak external current, suggesting that most of the dissipation is due to isolated vortices that traverse in a random potential. Following this picture, we constructed a single vortex model which quantitatively reproduces the RSJ simulation results. A key finding in our single-vortex simulations is that a finite lifetime should be assigned to the vortex, corresponding to a relaxation distance of about 7 lattice sites. If the time is enough, we can go further to discuss the vortex Nernst effect and the related probable 2D crystallization.  

Date&Time: March 1, 2013 (Friday), 14:30–15:30
Location: 606 Conference Room