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Exp. points: Hardy et al. PRB 81, 060501 (2010)

Thermodynamics and Dynamics of Superconducting Devices Maxim G. Vavilov, University of Wisconsin Madison, DMR 0955500.

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Exp. points: Hardy et al. PRB 81, 060501 (2010)

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  1. Thermodynamics and Dynamics of Superconducting DevicesMaxim G. Vavilov, University of Wisconsin Madison, DMR 0955500 • Recent discovery of novel iron-pnictide superconductors has stimulated massive theoretical and experimental research aimed at unveiling their unique properties. This research has high potential for applications in superconducting technologies. • We developed a theoretical model of iron-pnictides and applied this model to: • Establish conditions for a new thermodynamic phase with co-existence between magnetic and superconducting orders;1 • Evaluate the magnitude of the specific heat discontinuity at the superconducting transition from normal or spin-density wave phases and analyze experimental data (top figure);2 • Describe the differential conductance of contacts between iron-pnictide superconductors and normal metals (bottom figure).3 • The co-existence state was observed by a number of laboratories,andour theoretical curves are quantitatively consistent with experimental data (see figures). • References: 1Vorontsov, Vavilov, Chubukov, PRB 81, 174538 (2010); 2Vavilov, Chubukov, Vorontsov, arxiv:1104.5037; 3Kuzmanovski, Vavilov, arxiv:1105.3926. Specific heat jump doping Exp. points: Hardy et al. PRB 81, 060501 (2010) Transition temperature (in units of Tc,max) Differential conductance Bias voltage, mV Experimental curve: Lu et al., SUST 23, 054009 (2010).

  2. Thermodynamics and Dynamics of Superconducting DevicesMaxim G. Vavilov, University of Wisconsin Madison, DMR 0955500 • As part of another project, we study dynamics of superconducting devices for quantum information technologies. • We analyzed optimal microwave pulses for operation of a flux-biased qubit (an element for quantum computers).4 • We modeled the switching time for Josephson bifurcation amplifiers (potential read-out element for quantum computers) in the high-temperature limit. We plan to model the low-temperature limit soon. • The latter problem was also adopted as a part of an undergraduate course in classical mechanics to discuss classical non-linear and stochastic systems. We are working to develop web-based demonstrationsforthepublicto highlight featuresof non-linear and stochastic systems. • Currently, three PhD students are involved in projects supported by DMR award 0955500. • References: 4Poudel, Vavilov, PRB 82, 144528 (2010). Josephson bifurcation amplifier can be modeled by a driven Duffing oscillator. Amplitude r dependence on drive frequency w is a multi-value function: A B States A and B are steady solutions for a driven Duffing oscillator corresponding identical system parameters. System may spontaneously switch between these states due to fluctuations introduced by the oscillator environment.

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