G. P. Tsironis

University of Crete, Réthymnon, Kriti, Greece

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Publications (122)234.38 Total impact

  • G. P. Tsironis, N. Lazarides, I. Margaris
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    ABSTRACT: Superconducting metamaterials comprising rf SQUIDs (Superconducting QUantum Interference Devices) have been recently realized and investigated with respect to their tuneability, permeability and dynamic multistability properties. These properties are a consequence of intrinsic nonlinearities due to the sensitivity of the superconducting state to external stimuli. SQUIDs, made of a superconducting ring interrupted by a Josephson junction, possess yet another source of nonlinearity, which makes them widely tuneable with an applied dc dlux. A model SQUID metamaterial, based on electric equivalent circuits, is used in the weak coupling approximation to demonstrate the dc flux tuneability, dynamic multistability, and nonlinear transmission in SQUID metamaterials comprising non-hysteretic SQUIDs. The model equations reproduce the experimentally observed tuneability patterns, and predict tuneability with the power of an applied ac magnetic magnetic field. Moreover, the results indicate the opening of nonlinear frequency bands for energy transmission through SQUID metamaterials, for sufficiently strong ac fields.
    04/2014;
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    F. Perakis, M. Mattheakis, G. P. Tsironis
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    ABSTRACT: We use a simple dynamical model and explore coherent dynamics of wavepackets in complex networks of optical fibers. We start from a symmetric lattice and through the application of a Monte-Carlo criterion we introduce structural disorder and deform the lattice into a small-world network regime. We investigate in the latter both structural (correlation length) as well as dynamical (diffusion exponent) properties and find that both exhibit a rapid crossover from the ordered to the fully random regime. For a critical value of the structural disorder parameter $\rho \approx 0.25$ transport changes from ballistic to sub-diffusive due to the creation strongly connected local clusters and channels of preferential transport in the small world regime.
    01/2014;
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    ABSTRACT: The spatiotemporal complexity induced by perturbed initial excitations through the development of modulational instability in nonlinear lattices with or without disorder, may lead to the formation of very high amplitude, localized transient structures that can be named as extreme events. We analyze the statistics of the appearance of these collective events in two different universal lattice models; a one-dimensional nonlinear model that interpolates between the integrable Ablowitz-Ladik (AL) equation and the nonintegrable discrete nonlinear Schr\"odinger (DNLS) equation, and a two-dimensional disordered DNLS equation. In both cases, extreme events arise in the form of discrete rogue waves as a result of nonlinear interaction and rapid coalescence between mobile discrete breathers. In the former model, we find power-law dependence of the wave amplitude distribution and significant probability for the appearance of extreme events close to the integrable limit. In the latter model, more importantly, we find a transition in the the return time probability of extreme events from exponential to power-law regime. Weak nonlinearity and moderate levels of disorder, corresponding to weak chaos regime, favour the appearance of extreme events in that case.
    12/2013;
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    G. P. Tsironis, N. Lazarides
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    ABSTRACT: An overview of several dynamic properties of SQUID metamaterials is given in the presence of both constant and alternating magnetic field. The total current as a function of the driving frequency exhibits hysteretic effects which are favored by low levels of disorder. Multistability in the current states leads to multiple magnetic responses with different value of magnetic permeability. SQUID metamaterials exhibit wide-band tuneability which is periodic with the applied constant magnetic field; the numerical calculations reproduce fairly well recent experimental results. Current work also reveals the possibility for wave transmission through nonlinear bands, which is briefly discussed.
    12/2013;
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    N Lazarides, G P Tsironis
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    C. Athanasopoulos, M. Mattheakis, G. P. Tsironis
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    ABSTRACT: We present numerical simulations with COMSOL multiphysics software (FEM mode calculation method) one of the propagation of surface plasmons in a dielectric-metal-dielectric waveguide. We show that the use of an active dielectric, compensating the metallic absorption loss by gain, enhances plasmon propagation. The computational approaches demonstrated in this work can be used to define and tune the optimal conditions for which surface plasmons are generated and amplified.
    11/2013;
  • C. Athanasopoulos, M. Mattheakis, G. P. Tsironis
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    ABSTRACT: We present numerical simulations for the propagation of surface plasmon polaritons in a dielectric-metal-dielectric waveguide using COMSOL multiphysics software. We show that the use of an active dielectric with gain that compensates metal absorption losses enhances substantially plasmon propagation. Furthermore, the introduction of the active material induces, for a specific gain value, a root in the imaginary part of the propagation constant leading to infinite propagation of the surface plasmon. The computational approaches analyzed in this work can be used to define and tune the optimal conditions for surface plasmon polariton amplification and propagation.
    11/2013;
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    N. Lazarides, G. P. Tsironis
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    ABSTRACT: Metamaterials, i.e., artificially structured ("synthetic") media comprising weakly coupled discrete elements, exhibit extraordinary properties and they hold a great promise for novel applications including super-resolution imaging, cloaking, hyperlensing, and optical transformation. Nonlinearity adds a new degree of freedom for metamaterial design that allows for tuneability and multistability, properties that may offer altogether new functionalities and electromagnetic characteristics. The combination of discreteness and nonlinearity may lead to intrinsic localization of the type of discrete breather in metallic, SQUID-based, and ${\cal PT}-$symmetric metamaterials. We review recent results demonstrating the generic appearance of breather excitations in these systems resulting from power-balance between intrinsic losses and input power, either by proper initialization or by purely dynamical procedures. Breather properties peculiar to each particular system are identified and discussed. Recent progress in the fabrication of low-loss, active and superconducting metamaterials, makes the experimental observation of breathers in principle possible with the proposed dynamical procedures.
    10/2013;
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    N. Lazarides, G. P. Tsironis
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    ABSTRACT: Planar arrays of magnetoinductively coupled rf SQUIDs belong to the emergent class of superconducting metamaterials that encompass the Josephson effect. SQUID metamaterials acquire their electromagnetic properties from the resonant characteristics of their constitutive elements, i.e., the individual rf SQUIDs, which consist of a superconducting ring interrupted by a Josephson junction. We investigate the response of a two-dimensional SQUID metamaterial to frequency variation of an applied alternating magnetic field in the presence of disorder, arising from critical current fluctuations of the Josephson elements; in effect, the resonance frequencies of individual SQUIDs are distributed randomly around a mean value. Bistability is observed in the total current-frequency curves both in ordered and disordered SQUID metamaterials; moreover, bistability is favoured by disorder through the improvement of synchronization between SQUID oscillators. Relatively weak disorder widens significantly the bistability region by helping the system to self-organize itself and leads to nearly homogeneous states that change smoothly with varying frequency. Moreover, the total current of the metamaterial is enhanced compared with that of uncoupled SQUIDs, through the synergetic action of coupling and synchronization. Multistability of nearly homogeneous states allows the metamaterial to exhibit different magnetic responses corresponding to different values of the magnetic permeability. At low power of the incident field, high-current states exhibit extreme diamagnetic properties corresponding to negative magnetic permeability in a narrow frequency region.
    Superconductor Science and Technology 04/2013; 26(8). · 2.76 Impact Factor
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    G. P. Tsironis, N. Lazarides
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    ABSTRACT: A one dimensional, parity-time (PT)-symmetric magnetic metamaterial comprising split-ring resonators having both gain and loss is investigated. In the linear regime, the transition from the exact to the broken PT-phase is determined through the calculation of the eigenfrequency spectrum for two different configurations; the one with equidistant split-rings and the other with the split-rings forming a binary pattern (PT dimer chain). The latter system features a two-band, gapped spectrum with its shape determined by the gain/loss coefficient as well as the inter-element coupling. In the presense of nonlinearity, the PT dimer chain with balanced gain and loss supports nonlinear localized modes in the form of novel discrete breathers below the lower branch of the linear spectrum. These breathers, that can be excited from a weak applied magnetic field by frequency chirping, can be subsequently driven solely by the gain for very long times. The effect of a small imbalance between gain and loss is also considered. Fundamendal gain-driven breathers occupy both sites of a dimer, while their energy is almost equally partitioned between the two split-rings, the one with gain and the other with loss. We also introduce a model equation for the investigation of classical PT symmetry in zero dimensions, realized by a simple harmonic oscillator with matched time-dependent gain and loss that exhibits a transition from oscillatory to diverging motion. This behaviour is similar to a transition from the exact to the broken PT phase in higher-dimensional PT− symmetric systems. A stability condition relating the parameters of the problem is obtained in the case of piecewise constant gain/loss function that allows for the construction of a phase diagram with alternating stable and unstable regions.
    Applied Physics A 04/2013; · 1.55 Impact Factor
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    N Lazarides, G P Tsironis
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    ABSTRACT: We introduce a one-dimensional parity-time- (PT-)symmetric nonlinear magnetic metamaterial consisting of split-ring dimers having both gain and loss. When nonlinearity is absent we find a transition between an exact to a broken PT phase; in the former, the system features a two band gapped spectrum with shape determined by the gain and loss coefficients as well as the interunit coupling. In the presence of nonlinearity, we show numerically that as a result of the gain and dissipation matching a novel type of long-lived stable discrete breathers can form below the lower branch of the band with no attenuation. In these localized modes the energy is almost equally partitioned between two adjacent split rings on the one with gain and the other one with loss.
    Physical Review Letters 02/2013; 110(5):053901. · 7.94 Impact Factor
  • N. Lazarides, G. P. Tsironis
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    ABSTRACT: An array of rf SQUIDs (Superconducting Quantum Interference Devices) in an alternating magnetic field can operate as a magnetic metamaterial where the phase and group velocities have opposite signs. In this system, discreteness and nonlinearity may lead to the generation of intrinsic localized modes in the from of discrete breathers. These breathers result from a balance of incoming power and losses, and they may change locally the response of a SQUID array to an applied field from diamagnetic to paramagnetic or vice-versa. We derive the dynamic flux equations for the damped and driven SQUID array and integrate them in the weak-coupling approximation to demonstrate the existence of various kinds of dissipative breathers. Besides using standard algorithms for breather construction, we have also observed the spontaneous breather generation in weakly disordered SQUID arrays. Moreover, low-energy breather-like pulses may be generated in end-driven arrays which propagate for fairly long distances in a dissipative environment. A short account on the tunability of the resonance of individual SQUIDs by application of either constant and/or alternating fields is also given.
    Proc SPIE 05/2012;
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    ABSTRACT: Spatiotemporal complexity is induced in a two dimensional nonlinear disordered lattice through the modulational instability of an initially weakly perturbed excitation. In the course of evolution we observe the formation of transient as well as persistent localized structures, some of which have extreme magnitude. We analyze the statistics of occurrence of these extreme collective events and find that the appearance of transient extreme events is more likely in the weakly nonlinear regime. We observe a transition in the extreme events recurrence time probability from exponential, in the nonlinearity dominated regime, to power law for the disordered one.
    Physica D Nonlinear Phenomena 04/2012; 252. · 1.67 Impact Factor
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    ABSTRACT: We study the dynamics of the discrete nonlinear Schrödinger lattice initialized such that a very long transitory period of time in which standard Boltzmann statistics is insufficient is reached. Our study of the nonlinear system locked in this non-Gibbsian state focuses on the dynamics of discrete breathers (also called intrinsic localized modes). It is found that part of the energy spontaneously condenses into several discrete breathers. Although these discrete breathers are extremely long lived, their total number is found to decrease as the evolution progresses. Even though the total number of discrete breathers decreases we report the surprising observation that the energy content in the discrete breather population increases. We interpret these observations in the perspective of discrete breather creation and annihilation and find that the death of a discrete breather cause effective energy transfer to a spatially nearby discrete breather. It is found that the concepts of a multi-frequency discrete breather and of internal modes is crucial for this process. Finally, we find that the existence of a discrete breather tends to soften the lattice in its immediate neighborhood, resulting in high amplitude thermal fluctuation close to an existing discrete breather. This in turn nucleates discrete breather creation close to a already existing discrete breather. PACS. 63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions - 63.20.Pw Localized modes - 63.20.Ry Anharmonic lattice modes
    Physics of Condensed Matter 04/2012; 15(1):169-175. · 1.28 Impact Factor
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    M I Molina, N Lazarides, G P Tsironis
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    ABSTRACT: We investigate numerically the effect of the competition of disorder, nonlinearity, and boundaries on the Anderson localization of light waves in finite-size, one-dimensional waveguide arrays. Using the discrete Anderson-nonlinear Schrödinger equation, the propagation of the mode amplitudes up to some finite distance is monitored. The analysis is based on the calculated localization length and the participation number, two standard measures for the statistical description of Anderson localization. For relatively weak disorder and nonlinearity, a higher disorder strength is required to achieve the same degree of localization at the edge than in the interior of the array, in agreement with recent experimental observations in the linear regime. However, for relatively strong disorder and/or nonlinearity, this behavior is reversed and it is now easier to localize an excitation at the edge than in the interior.
    Physical Review E 01/2012; 85(1 Pt 2):017601. · 2.31 Impact Factor
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    ABSTRACT: We investigate in the framework of Landau theory the distortion of the strain fields at the interface of two dissimilar ferroelastic oxides that undergo a structural cubic-to-tetragonal phase transition. Simple analytical solutions are derived for the dilatational and the order parameter strains that are globally valid over the whole of the heterostructure. The solutions reveal that the dilatational strain exhibits compression close to the interface which may in turn affect the electronic properties in that region.
    Physical review. B, Condensed matter 05/2011;
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    G. P. Tsironis
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    ABSTRACT: We investigate the dynamics of the discrete nonlinear Schr\"{o}dinger equation in fully connected networks. For a localized initial condition the exact solution shows the existence of two dynamical transitions as a function of the nonlinearity parameter, a hyperbolic and a trigonometric one. In the latter the network behaves exactly as the corresponding linear one but with a renormalized frequency.
    Physics Letters A 01/2011; 375(10). · 1.77 Impact Factor
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    ABSTRACT: Power transmission in one-dimensional nonlinear magnetic metamaterials driven at one end is investigated numerically and analytically in a wide frequency range. The nonlinear magnetic metamaterials are composed of varactor-loaded split-ring resonators which are coupled magnetically through their mutual inductances, forming thus a magnetoiductive transmission line. In the linear limit, significant power transmission along the array only appears for frequencies inside the linear magnetoinductive wave band. We present analytical, closed form solutions for the magnetoinductive waves transmitting the power in this regime, and their discrete frequency dispersion. When nonlinearity is important, more frequency bands with significant power transmission along the array may appear. In the equivalent circuit picture, the nonlinear magnetoiductive transmission line driven at one end by a relatively weak electromotive force, can be modeled by coupled resistive-inductive-capacitive (RLC) circuits with voltage-dependent capacitance. Extended numerical simulations reveal that power transmission along the array is also possible in other than the linear frequency bands, which are located close to the nonlinear resonances of a single nonlinear RLC circuit. Moreover, the effectiveness of power transmission for driving frequencies in the nonlinear bands is comparable to that in the linear band. Power transmission in the nonlinear bands occurs through the linear modes of the system, and it is closely related to the instability of a mode that is localized at the driven site.
    International Journal of Bifurcation and Chaos 01/2011; 21. · 0.92 Impact Factor
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    F. Perakis, G.P. Tsironis
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    ABSTRACT: We investigate dynamical aspects of the discrete nonlinear Schrödinger equation in finite lattices. Starting from a periodic chain with nearest neighbor interactions, we insert randomly links connecting distant pairs of sites across the lattice. Using localized initial conditions we focus on the time averaged probability of occupation of the initial site as a function of the degree of complexity of the lattice and nonlinearity. We observe that selftrapping occurs at increasingly larger values of the nonlinearity parameter as the lattice connectivity increases, while close to the fully coupled network limit, localization becomes more preferred. For nonlinearity values above a certain threshold we find a reentrant localization transition, viz. localization when the number of long distant bonds is small followed by delocalization and enhanced transport at intermediate bond numbers while close to the fully connected limit localization reappears.
    Physics Letters A 01/2011; · 1.77 Impact Factor
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    N. Lazarides, M.I. Molina, G.P. Tsironis
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    ABSTRACT: The existence and stability of discrete breathers is studied theoretically for a model magnetic metamaterial composed of a periodic binary array of split-ring resonators with resonance frequency mismatch. It is demonstrated that breathers can be excited spontaneously by frequency chirping of the driving field, a method that is well suited for experiments.
    Physica B Condensed Matter 07/2010; · 1.33 Impact Factor

Publication Stats

791 Citations
705 Downloads
234.38 Total Impact Points

Institutions

  • 1996–2013
    • University of Crete
      • • Department of Physics
      • • Department of Materials Science and Technology
      Réthymnon, Kriti, Greece
  • 2009–2012
    • University of Santiago, Chile
      • Departamento de Física
      Santiago, Region Metropolitana de Santiago, Chile
  • 1999–2012
    • Los Alamos National Laboratory
      • Center for Nonlinear Studies
      Los Alamos, NM, United States
    • Freie Universität Berlin
      • Institute of Theoretical Physics
      Berlin, Land Berlin, Germany
  • 2011
    • University of Zurich
      • Institut für Physikalische Chemie
      Zürich, Zurich, Switzerland
  • 2010
    • Technological Educational Institute of Crete
      • Department of Electrical Engineering
      Megalokastro, Crete, Greece
  • 2007
    • Ruhr-Universität Bochum
      • Fakultät für Physik und Astronomie
      Bochum, North Rhine-Westphalia, Germany
  • 2002–2007
    • University of Barcelona
      • Department of Structure and Constituents of Matter
      Barcino, Catalonia, Spain
  • 2005–2006
    • Foundation for Research and Technology - Hellas
      Megalokastro, Crete, Greece
    • Nagasaki Institute of Applied Science
      Nagasaki, Nagasaki, Japan
  • 1992–1998
    • University of North Texas
      • Department of Physics
      Denton, TX, United States
    • Cornell University
      Ithaca, New York, United States
    • University of California, San Diego
      • Institute for Nonlinear Science (INLS)
      San Diego, CA, United States