Phase oscillations in superfluid 3He-B weak links

Oscillations in quantum phase about a mean value of $\pi$, observed across micropores connecting two \helium baths, are explained in a Ginzburg-Landau phenomenology. The dynamics arises from the Josephson phase relation,the interbath continuity equation, and helium boundary conditions. The pores are shown to act as Josephson tunnel junctions, and the dynamic variables are the inter bath phase difference and fractional difference in superfluid density at micropores. The system maps onto a non-rigid, momentum-shortened pendulum, with inverted-orientation oscillations about a vertical tilt angle $\phi = \pi$, and other modes are predicted

Re-equilibration after quenches in athermal martensites:Conversion-delays for vapour to liquid domain-wall phases

Entropy barriers and ageing states appear in martensitic structural-transition models, slowly re-equilibrating after temperature quenches, under Monte Carlo dynamics. Concepts from protein folding and ageing harmonic oscillators turn out to be useful in understanding these nonequilibrium evolutions. We show how the athermal, non-activated delay time for seeded parent-phase austenite to convert to product-phase martensite, arises from an identified entropy barrier in Fourier space. In an ageing state of low Monte Carlo acceptances, the strain structure factor makes constant-energy searches for rare pathways, to enter a Brillouin zone `golf hole' enclosing negative energy states, and to suddenly release entropically trapped stresses. In this context, a stress-dependent effective temperature can be defined, that re-equilibrates to the quenched bath temperature.Comment: 11 pages, 12 figures. Under process with Phys. Rev. B (2015

Theoretical calculations of radiant heat transfer properties of particle-seeded gases

Radiant heat transfer properties of particle seeded gases, including absorption and scattering characteristics of carbon, silicon, and tungste

Nonequilibrium phase transition in a radiation-driven Josephson junction

We predict that a nonequilibrium phase transition, analogous to optical bistability, occurs when coherent radiation is applied to an unbiased Josephson junction with an external resistance across it. The order parameter is the self-consistently developed dc voltage, and the drive parameter is the applied radiation intensity. The order parameter exhibits jump and hysteresis behavior characteristic of a first-order phase transition. The size of the hysteresis region can be tuned by varying the resistance. An approach based on the Fokker-Planck equation is adopted. The extremum of the stationary probability yields the self-consistency equation for the mean-field order parameter. Relaxation and decay times are calculated, the decay times being identified with the first passage time. Estimates of parameters show that the bistable regime could be experimentally accessible

Exponent behavior at a dissipative phase transition of a driven Josephson junction

Static and dynamic critical exponents and a set of spinodal exponents are calculated within a mean-field approximation for the case of a driven Josephson junction undergoing a nonequilibrium phase transition. These universal exponents obey the exponent relations obtained from scaling-for-equilibrium phase transitions. The exponents are directly related to experimental observables such as the junction voltage, its noise bandwidth, and the Josephson radiation linewidth

Radiation-induced bistability in Josephson junctions

It is predicted that a nonequilibrium first-order phase transition analogous to optical bistability can occur when external coherent radiation is applied to a suitably prepared Josephson junction with an external resistance across it. The size of the hysteresis region can be tuned by varying the resistance

Three-Dimensional Elastic Compatibility: Twinning in Martensites

We show how the St.Venant compatibility relations for strain in three dimensions lead to twinning for the cubic to tetragonal transition in martensitic materials within a Ginzburg-Landau model in terms of the six components of the symmetric strain tensor. The compatibility constraints generate an anisotropic long-range interaction in the order parameter (deviatoric strain) components. In contrast to two dimensions, the free energy is characterized by a "landscape" of competing metastable states. We find a variety of textures, which result from the elastic frustration due to the effects of compatibility. Our results are also applicable to structural phase transitions in improper ferroelastics such as ferroelectrics and magnetoelastics, where strain acts as a secondary order parameter