M. I. Molina

University of Santiago, Chile, Santiago, Region Metropolitana de Santiago, Chile

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Publications (17)39.52 Total impact

  • D Chen, M I Molina, G P Tsironis
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    ABSTRACT: We study the dynamics of non-adiabatic Holstein-type impurities embedded in an infinite linear chain. The impurities are modelled as Einstein oscillators coupled to specific sites of an infinite one-dimensional tight-binding host. We present numerical evidence providing bounds for the onset of self-trapping that depend critically on the initial conditions of the oscillators. We show that, in general, small but finite oscillator masses do not substantially change the self-trapped character of the states. For intermediate as well as large oscillator masses self-trapping can still occur for some initial oscillator preparations.
    Journal of Physics Condensed Matter 12/1998; 5(46):8689. · 2.22 Impact Factor
  • N Sun, D Hennig, M I Molina, G P Tsironis
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    ABSTRACT: We study the transmission problem for electrons in an alternately linear-non-linear medium using a quasiperiodic Kronig-Penney model whose variance in spatial locations obeys the Fibonacci rules. We find that for waves with low intensity and long wavelength, non-linearity enhances the lattice transparency.
    Journal of Physics Condensed Matter 12/1998; 6(38):7741. · 2.22 Impact Factor
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    D Chen, M I Molina, G P Tsironis
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    ABSTRACT: We study propagation of excitations in one-dimensional tight-binding chains doped with random impurities that are classical Einstein oscillators. We find that the presence of impurities does not affect substantially the ballistic nature of the electronic propagation. Furthermore, for some oscillator masses, wave propagation is faster than that of the ordered tight-binding chain.
    Journal of Physics Condensed Matter 12/1998; 8(37):6917. · 2.22 Impact Factor
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    M. I. Molina, J. A Roessler
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    ABSTRACT: We study an ideal Bose gas of N atoms contained in a box formed by two identical planar and parallel surfaces S, enclosed by a mantle of height a perpendicular to them. Calling r0 the mean atomic distance, we assume S >> r0^2 while a may be comparable to r0. In the bidimensional limit (a/r0 << 1) we find a macroscopic number of atoms in the condensate at temperatures T ~1/log(N); therefore, condensation cannot be described in terms of intensive quantities; in addition, it occurs at temperatures not too low in comparison to the tridimensional case. When condensation is present we also find a macroscopic occupation of the low--lying excited states. In addition, the condensation phenomenon is sensitive to the shape of S. The former two effects are significant for a nanoscopic system. The tridimensional limit is slowly attained for increasing (a/r0), roughly at (a/r0) ~ 10^{2}-10^{3}.
    05/1997;
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    M. I. Molina, J. A Roessler, G. P. Tsironis
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    ABSTRACT: We perform a fully quantum mechanical numerical calculation for the problem of a single electron (or excitation) propagating in a N-site one-dimensional chain in the presence of a single Holstein impurity. We compute the long-time averaged probability for finding the electron on the impurity site as a function of the nonlinearity parameter, defined in terms of the electron-phonon coupling strength and the oscillator frequency. The results, in the intermediate nonlinearity parameter range, differ substantially from the ones obtained through the use of the discrete nonlinear Schroedinger equation, even in the high-frequency regime. Comment: 8 pages, 4 figures
    Physics Letters A 04/1997; · 1.77 Impact Factor
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    W.D. Deering, M.I. Molina
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    ABSTRACT: We report on a theoretical and numerical investigation of the switching of power in new hybrid models of nonlinear coherent couplers consisting of optical slab waveguides with various orders of nonlinearity. The first model consists of two guides with second-order instead of the usual third-order susceptibilities as typified by the Jensen coupler. This second-order system is shown to have a power self-trapping transition at a critical power greater than the third-order susceptibility coupler. Next, we consider a mixed coupler composed of a second-order guide coupled to a third-order guide and show that, although it does not display a rigorous self-trapping transition, for a particular choice of parameters it does show a fairly abrupt trapping of power at a lower power than in the third-order coupler. By coupling this mixed nonlinear pair to a third, purely linear guide, the power trapping can be brought to even lower levels and in this way a satisfactory switching profile can be achieved at less than one sixth the input power needed in the Jensen coupler
    IEEE Journal of Quantum Electronics 04/1997; · 1.83 Impact Factor
  • M. I. Molina, G. P. Tsironis
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    ABSTRACT: We study the interplay of disorder and nonlinearity in condensed matter systems modeled by the paradigmatic discrete nonlinear Schrödinger equation and focus on selftrapping and transport properties. We start by analyzing the two most simple nonlinear disordered systems, viz. a nondegenerate nonlinear dimer and a perturbed degenerate dimer. We then consider the case of few nonlinear impurities embedded in a linear host and treat the stationary problem analytically. We conclude by examining the case of a one-dimensional nonlinear random binary alloy where we find absence of quasiparticle localization, except for large nonlinearity parameter values. The transmission of plane’ waves across a disordered nonlinear segment of this type shows a power-law decay as a function of the segment size.
    International Journal of Modern Physics B 01/1995; 9(16):1899-1932. · 0.36 Impact Factor
  • GP Tsironis, MI Molina, D Hennig
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    ABSTRACT: We study the problem of one nonlinear impurity embedded in a linear tight-binding host. The impurity is of the type found in the generalized discrete nonlinear Schrödinger equation. We obtain analytically a phase diagram that describes the presence of bound states for different nonlinearity parameter values and nonlinearity exponents. We find that two impurity states are possible in some parameter regimes. From the numerical solution of the complete dynamical problem we obtain information on the nonlinear site survival probability that shows a dynamical self-trapping that is compatible with the findings of the stationary-state analysis.
    Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 10/1994; 50(3):2365-2368.
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    MI Molina, GP Tsironis
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    ABSTRACT: We investigate electronic propagation in a one-dimensional nonlinear random binary alloy modeled by a discrete nonlinear Schrödinger equation. We find absence of electronic localization except for large nonlinearity parameter values. The presence of disorder is completely overcome by the nonlinear terms leading to ballistic propagation of the untrapped electronic fraction. The existence of disorder in the model is manifested in the power-law decay of the transmissivity of plane waves through the medium as a function of the system size.
    Physical Review Letters 08/1994; 73(3):464-467. · 7.73 Impact Factor
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    ABSTRACT: We investigate wave propagation in a superlattice consistent of dielectric material with a nonlinear Kerr coefficient. We find gaps in the propagating properties of the medium that depend critically on the injected wave power. This property can be used for transmission of information.
    Applied Physics Letters 06/1994; · 3.79 Impact Factor
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    ABSTRACT: We introduce a quasiperiodic nonlinear Kronig-Penney model with a sequence of barrier heights constructed according to the Fibonacci inflation rule. We find that nonlinearlity enhances tranparency and reduces the localization properties of the corresponding linear quasiperiodic Kronig-Penney model.
    Physics Letters A 01/1994; 190:259-263. · 1.77 Impact Factor
  • G.P. Tsironis, W.D. Deering, M.I. Molina
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    ABSTRACT: We present two generalizations to standard optical coupler configurations. Both cases show improved switching characteristics.
    Physica D Nonlinear Phenomena 09/1993; 68(1):135–137. · 1.67 Impact Factor
  • MI Molina, GP Tsironis
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    ABSTRACT: We use the Green's function formalism to evaluate analytically the stationary states for an electron moving in a one-dimensional chain in the presence of one and two adiabatic Holstein-type [ital nonlinear] impurities. For the case of one nonlinear monomer we find that, contrary to what occurs in the linear impurity problem, the strength of the impurity must be greater than half the bandwidth for a bound state to exist. In the case of a nonlinear dimer resonance phenomena are observed that lead to [ital complete] transmission through the dimer.
    Physical review. B, Condensed matter 07/1993; 47(22):15330-15333. · 3.77 Impact Factor
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    W. D. Deering, M. I. Molina, G. P. Tsironis
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    ABSTRACT: The switching characteristics of simple mixed linear–nonlinear configurations of directional couplers for single‐mode operation are investigated. For negative interaction coefficients, faster switching can be achieved at lower input power levels than in all‐nonlinear coupler configurations.  
    Applied Physics Letters 06/1993; · 3.79 Impact Factor
  • M.I. Molina, G.P. Tsironis
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    ABSTRACT: We study dynamical aspects of the discrete nonlinear Schrödinger equation (DNLS) for chains of different sizes with periodic and open boundary conditions. We focus on the occurrence of a self-trapping transition in the different geometries. The initial condition used is that which places the particle (or power) on one lattice site (or nonlinear waveguide) and the quantity studied is the time-averaged probability for the particle to remain in that site. We show that the self-trapping transition in long chains occurs for parameter values not very different from that for very small clusters.
    Physica D Nonlinear Phenomena 05/1993; · 1.67 Impact Factor
  • M.I. Molina, W.D. Deering, G.P. Tsironis
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    ABSTRACT: We introduce an optical coupler configuration consisting of two nonlinear waveguides coupled to a linear one. Selftrapping of electric field amplitude is possible in each nonlinear waveguide arising from the nonlinear field-dependent dielectric coefficient. We show that this coupler system can act as an optical switching device and it can have switching properties superior to that of conventional two and three all nonlinear coupler configurations.
    Physica D Nonlinear Phenomena 01/1993; · 1.67 Impact Factor
  • MI Molina, GP Tsironis
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    ABSTRACT: We study the persistence of self-trapping in the presence of arbitrary large perturbations. We obtain the phase diagram for a nonlinear dimer interacting with a third linear impurity site and show that the abrupt Kenkre-Campbell transition is sustained. In addition to the ``free'' and ``self-trapped'' regimes we find a ``chaotic'' regime for some well-defined values of the nonlinearity and linear coupling parameters.
    Physical Review A 08/1992; 46(2):1124-1127. · 3.04 Impact Factor

Publication Stats

324 Citations
39.52 Total Impact Points

Institutions

  • 1997–1998
    • University of Santiago, Chile
      • Departamento de Física
      Santiago, Region Metropolitana de Santiago, Chile
  • 1993–1998
    • University of North Texas
      • Department of Physics
      Denton, TX, United States