External Electric Field Mediated Quantum Phase Transitions in One-Dimensional Charge Ordered Insulators: A DMRG Study

We perform density matrix renormalization group (DMRG) calculations extensively on one-dimensional chains with on site (U) as well as nearest neighbour (V) Coulomb repulsions. The calculations are carried out in full parameter space with explicit inclusion of the static bias and we compare the nature of spin density wave (SDW) and charge density wave (CDW) insulators under the influence of external electric field. We find that, although the SDW (U>2V) and CDW (U<2V) insulators enter into a conducting state after a certain threshold bias, CDW insulators require much higher bias than the SDW insulators for insulator-metal transition at zero temperature. We also find the CDW-SDW phase transition on application of external electric field. The bias required for the transitions in both cases decreases with increase in system size.Comment: 7 pages, 7 figures, accepted in J. Phys.: Condens. Matte

Bayes Model Selection with Path Sampling: Factor Models and Other Examples

We prove a theorem justifying the regularity conditions which are needed for Path Sampling in Factor Models. We then show that the remaining ingredient, namely, MCMC for calculating the integrand at each point in the path, may be seriously flawed, leading to wrong estimates of Bayes factors. We provide a new method of Path Sampling (with Small Change) that works much better than standard Path Sampling in the sense of estimating the Bayes factor better and choosing the correct model more often. When the more complex factor model is true, PS-SC is substantially more accurate. New MCMC diagnostics is provided for these problems in support of our conclusions and recommendations. Some of our ideas for diagnostics and improvement in computation through small changes should apply to other methods of computation of the Bayes factor for model selection.Comment: Published in at http://dx.doi.org/10.1214/12-STS403 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Dynamical Structure Factor of Fulde-Ferrell-Larkin-Ovchinnikov Superconductors

Superconductor with a spatially-modulated order parameter is known as Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor. Using the time-dependent Ginzburg-Landau (TDGL) formalism we have theoretically studied the temporal behaviour of the equal-time correlation function, or the structure factor, of a FFLO superconductor following a sudden quench from the unpaired, or normal, state to the FFLO state. We find that quenching into the ordered FFLO phase can reveal the existence of a line in the mean-field phase diagram which cannot be accessed by static properties.Comment: 2 pages, Poster presented at 57TH DAE SOLID STATE PHYSICS SYMPOSIUM, 2012. Mainly based on arXiv:1210.220