arXiv subjects

N. Lazarides

Publications and source records attributed to N. Lazarides.

43 records · Page 3Linked to original sources

arXiv2007

Mobile $π-$kinks and half-integer zero-field-like steps in highly discrete alternating $0-π$ Josephson junction arrays

The dynamics of a one-dimensional, highly discrete, linear array of alternating $0-$ and $π-$ Josephson junctions is studied numerically, under constant bias current at zero magnetic field. The calculated current - voltage characteristics exhibit half-integer and integer zero-field-like steps for even and odd total number of junctions, respectively. Inspection of the instantaneous phases reveals that, in the former case, single $π-$kink excitations (discrete semi-fluxons) are supported, whose propagation in the array gives rise to the $1/2-$step, while in the latter case, a pair of $π-$kink -- $π-$antikink appears, whose propagation gives rise to the $1-$step. When additional $2π-$kinks are inserted in the array, they are subjected to fractionalization, transforming themselves into two closely spaced $π-$kinks. As they propagate in the array along with the single $π-$kink or the $π-$kink - $π-$antikink pair, they give rise to higher half-integer or integer zero-field-like steps, respectively.

cond-mat.supr-con↗

arXiv2007

Magnetoinductive breathers in magnetic metamaterials

The existence and stability of discrete breathers (DBs) in one-dimensional and two-dimensional magnetic metamaterials (MMs), which consist of periodic arrangem ents (arrays) of split-ring resonators (SRRs), is investigated numerically. We consider different configurations of the SRR arrays, which are related to the relative orientation of the SRRs in the MM, both in one and two spatial dimensions. In the latter case we also consider anisotropic MMs. Using standard numerical methods we construct several types of linearly stable breather excitations both in Hamiltonian and dissipative MMs (dissipative breathers). The study of stability in both cases is performed using standard Floquet analysi s. In both cases we found that the increase of dimensionality from one to two spatial dimensions does not destroy the DBs, which may also exist in the case of moderate anisotropy (in two dimensions). In dissipative MMs, the dynamics is governed by a power balance between the mainly Ohmic dissipation and driving by an alternating magnetic field. In that case it is demonstrated that DB excitation locally alters the magnetic response of MMs from paramagnetic to diamagnetic. Moreover, when the frequency of the applied field approaches the SRR resonance frequency, the magnetic response of the MM in the region of the DB excitation may even become negative (extreme diamagnetic).

cond-mat.mtrl-sci↗

arXiv2007

rf SQUID metamaterials

An rf superconducting quantum interference device (SQUID) array in an alternating magnetic field is investigated with respect to its effective magnetic permeability, within the effective medium approximation. This system acts as an inherently nonlinear magnetic metamaterial, leading to negative magnetic response, and thus negative permeability, above the resonance frequency of the individual SQUIDs. Moreover, the permeability exhibits oscillatory behavior at low field intensities, allowing its tuning by a slight change of the intensity of the applied field.

cond-mat.mtrl-sci↗

arXiv2006

Self-focusing and envelope pulse generation in nonlinear magnetic metamaterials

The self-modulation of waves propagating in nonlinear magnetic metamaterials is investigated. Considering the propagation of a modulated amplitude magnetic field in such a medium, we show that the self-modulation of the carrier wave leads to a spontaneous energy localization via the generation of localized envelope structures (envelope solitons), whose form and properties are discussed. These results are also supported by numerical calculations.

cond-mat.mtrl-sci↗

arXiv2006

Discrete breathers in nonlinear magnetic metamaterials

Magnetic metamaterials composed of split-ring resonators or $U-$type elements may exhibit discreteness effects in THz and optical frequencies due to weak coupling. We consider a model one-dimensional metamaterial formed by a discrete array of nonlinear split-ring resonators with each ring interacting with its nearest neighbours. On-site nonlinearity and weak coupling among the individual array elements result in the appearence of discrete breather excitations or intrinsic localized modes, both in the energy-conserved and the dissipative system. We analyze discrete single and multibreather excitations, as well as a special breather configuration forming a magnetization domain wall and investigate their mobility and the magnetic properties their presence induces in the system.

cond-mat.mtrl-sci↗

arXiv2005

Coupled nonlinear Schroedinger field equations for electromagnetic wave propagation in nonlinear left-handed materials

For an isotropic and homogeneous nonlinear left-handed materials, for which the effective medium approximation is valid, Maxwell's equations for electric and magnetic fields lead naturally, within the slowly varying envelope approximation, to a system of coupled nonlinear Schroedinger equations. This system is equivalent to the well-known Manakov model that under certain conditions, is completely integrable and admits bright and dark soliton solutions. It is demonstrated that left- and right-handed (normal) nonlinear mediums may have compound bright and dark soliton solutions, respectively. These results are also supported by numerical calculations.

nlin.PS↗

arXiv2003

Josephson effect in double-barrier superconductor-ferromagnet junctions

We study the Josephson effect in ballistic double-barrier SIFIS planar junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet (F), and insulating interfaces (I). We solve the scattering problem based on the Bogoliubov--de Gennes equations and derive a general expression for the dc Josephson current, valid for arbitrary interfacial transparency and Fermi wave vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle transmission resonances contribute significantly to the Andreev process. The Josephson current is calculated for various parameters of the junction, and the influence of both interfacial transparency and FWVM is analyzed. For thin layers of strong ferromagnet and finite interfacial transparency, we find that coherent (geometrical) oscillations of the maximum Josephson current are superimposed on the oscillations related to the crossover between 0 and $π$ states. For the same case we find that the temperature-induced $0-π$ transition occurs if the junction is very close to the crossovers at zero temperature.

cond-mat.supr-con↗