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Search Results: 1 - 10 of 200906 matches for " Jaime E. Santos "
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Non-equilibrium behavior at a liquid-gas critical point
Jaime E. Santos,Uwe C. Tauber
Physics , 2002, DOI: 10.1140/epjb/e2002-00246-2
Abstract: Second-order phase transitions in a non-equilibrium liquid-gas model with reversible mode couplings, i.e., model H for binary-fluid critical dynamics, are studied using dynamic field theory and the renormalization group. The system is driven out of equilibrium either by considering different values for the noise strengths in the Langevin equations describing the evolution of the dynamic variables (effectively placing these at different temperatures), or more generally by allowing for anisotropic noise strengths, i.e., by constraining the dynamics to be at different temperatures in d_par- and d_perp-dimensional subspaces, respectively. In the first, case, we find one infrared-stable and one unstable renormalization group fixed point. At the stable fixed point, detailed balance is dynamically restored, with the two noise strengths becoming asymptotically equal. The ensuing critical behavior is that of the standard equilibrium model H. At the novel unstable fixed point, the temperature ratio for the dynamic variables is renormalized to infinity, resulting in an effective decoupling between the two modes. We compute the critical exponents at this new fixed point to one-loop order. For model H with spatially anisotropic noise, we observe a critical softening only in the d_perp-dimensional sector in wave vector space with lower noise temperature. The ensuing effective two-temperature model H does not have any stable fixed point in any physical dimension, at least to one-loop order. We obtain formal expressions for the novel critical exponents in a double expansion about the upper critical dimension d_c = 4 - d_par and with respect to d_par, i.e., about the equilibrium theory.
Dipolar Interactions in Superconductor-Ferromagnet Heterostructures
Jaime E. Santos,Erwin Frey,Franz Schwabl
Physics , 2000, DOI: 10.1103/PhysRevB.63.054439
Abstract: We consider a simple model for a superlattice composed of a thin magnetic film placed between two bulk superconductors. The magnetic film is modelled by a planar but otherwise arbitrary distribution of magnetic dipoles and the superconductors are treated in the London approximation. Due to the linearity of the problem, we are able to compute the magnetic energy of the film in the presence of the superconductors. We show that in the case of small wavenumbers compared to the inverse London penetration depth, the magnetic energy resembles the energy of a distribution of magnetisation in a two dimensional space. Possible experimental applications of these results are discussed.
The distribution of work performed on a NIS junction
Jaime E. Santos,Pedro Ribeiro,Stefan Kirchner
Physics , 2015,
Abstract: We propose an experimental setup to measure the work performed in a normal-metal/insulator/superconducting (NIS) junction, subjected to a voltage change and in contact with a thermal bath. We compute the performed work and argue that the associated heat release can be measured experimentally. Our results are based on an equivalence between the dynamics of the NIS junction and that of an assembly of two-level systems subjected to a circularly polarised field, for which we can determine the work-characteristic function exactly. The average heat dissipated by the NIS junction, as well as its fluctuations, are determined. From the work characteristic function, we also compute the work probability-distribution and show that it does not have a Gaussian character. Our results allow for a direct experimental test of the Crooks-Tasaki fluctuation relation.
Domain wall roughening in dipolar films in the presence of disorder
Jaime E. Santos,Erwin Frey,Franz Schwabl
Physics , 2001, DOI: 10.1103/PhysRevE.65.031608
Abstract: We derive a low-energy Hamiltonian for the elastic energy of a N\'eel domain wall in a thin film with in-plane magnetization, where we consider the contribution of the long-range dipolar interaction beyond the quadratic approximation. We show that such a Hamiltonian is analogous to the Hamiltonian of a one-dimensional polaron in an external random potential. We use a replica variational method to compute the roughening exponent of the domain wall for the case of two-dimensional dipolar interactions.
Non-equilibrium tube length fluctuations of entangled polymers
Gunter M. Schuetz,Jaime E. Santos
Physics , 2001, DOI: 10.1063/1.1374557
Abstract: We investigate the nonequilibrium tube length fluctuations during the relaxation of an initially stretched, entangled polymer chain. The time-dependent variance $\sigma^2$ of the tube length follows in the early-time regime a simple universal power law $\sigma^2 = A \sqrt{t}$ originating in the diffusive motion of the polymer segments. The amplitude $A$ is calculated analytically both from standard reptation theory and from an exactly solvable lattice gas model for reptation and its dependence on the initial and equilibrium tube length respectively is discussed. The non-universality suggests the measurement of the fluctuations (e.g. using flourescence microscopy) as a test for reptation models.
Strong light-matter interaction in systems described by a modified Dirac equation
N. M. R. Peres,Jaime E. Santos
Physics , 2013, DOI: 10.1088/0953-8984/25/30/305801
Abstract: The bulk states of some materials, such as topological insulators, are described by a modified Dirac equation. Such systems may have trivial and non-trivial phases. In this paper, we show that in the non-trivial phase a strong light-matter interaction exists in a two-dimensional system, which leads to an optical conductivity at least one order of magnitude larger than that of graphene.
Evolution of squeezed states under the Fock-Darwin Hamiltonian
Jaime E. Santos,Nuno M. Peres,Joao Lopes dos Santos
Physics , 2009, DOI: 10.1103/PhysRevA.80.053401
Abstract: We develop a complete analytical description of the time evolution of squeezed states of a charged particle under the Fock-Darwin Hamiltonian and a time-dependent electric field. This result generalises a relation obtained by Infeld and Pleba\'nski for states of the one-dimensional harmonic oscillator. We relate the evolution of a state-vector subjected to squeezing to that of state which is not subjected to squeezing and for which the time-evolution under the simple harmonic oscillator dynamics is known (e.g. an eigenstate of the Hamiltonian). A corresponding relation is also established for the Wigner functions of the states, in view of their utility in the analysis of cold-ion experiments. In an appendix, we compute the response functions of the FD Hamiltonian to an external electric field, using the same techniques as in the main text.
Diffusion-annihilation dynamics in one spatial dimension
Jaime E. Santos,Gunter M. Schutz,Robin B. Stinchcombe
Physics , 1996, DOI: 10.1063/1.472107
Abstract: We discuss a reaction-diffusion model in one dimension subjected to an external driving force. Each lattice site may be occupied by at most one particle. The particles hop with asymmetric rates (the sum of which is one) to the right or left nearest neighbour site if it is vacant, and annihilate with rate one if it is occupied. We compute the long time behaviour of the space dependent average density in states where the initial density profiles are step functions. We also compute the exact time dependence of the particle density for uncorrelated random initial conditions. The representation of the uncorrelated random initial state and also of the step function profile in terms of free fermions allows the calculation of time-dependent higher order correlation functions. We outline the procedure using a field theoretic approach.
Renewal processes and fluctuation analysis of molecular motor stepping
Jaime E. Santos,Thomas Franosch,Andrea Parmeggiani,Erwin Frey
Physics , 2005, DOI: 10.1088/1478-3975/2/3/008
Abstract: We model the dynamics of a processive or rotary molecular motor using a renewal processes, in line with the work initiated by Svoboda, Mitra and Block. We apply a functional technique to compute different types of multiple-time correlation functions of the renewal process, which have applications to bead-assay experiments performed both with processive molecular motors, such as myosin V and kinesin, and rotary motors, such as F1-ATPase.
The effects of violating detailed balance on critical dynamics
Uwe C. Tauber,Vamsi K. Akkineni,Jaime E. Santos
Physics , 2001, DOI: 10.1103/PhysRevLett.88.045702
Abstract: We present an overview of the effects of detailed-balance violating perturbations on the universal static and dynamic scaling behavior near a critical point. It is demonstrated that the standard critical dynamics universality classes are generally quite robust: In systems with non-conserved order parameter, detailed balance is effectively restored at criticality. This also holds for models with conserved order parameter, and isotropic non-equilibrium perturbations. Genuinely novel features are found only for models with conserved order parameter and spatially anisotropic noise correlations.
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