arXiv subjects

Yu. A. Genenko

Publications and source records attributed to Yu. A. Genenko.

15 recordsLinked to original sources

arXiv2011

Superconducting wires under simultaneous oscillating sources: involved magnetic response, dissipation of energy and low pass filtering

Numerical simulations of filamentary type II superconducting wires under simultaneous AC transport current and oscillating transverse magnetic fields are performed within the critical state approximation. The time dependences of the current density profiles, magnetic flux lines, local power dissipation and magnetic moment are featured. Noticeable non-homogeneous dissipation and field distortions are displayed. Also, significant differences between the obtained AC-losses and those predicted by regular approximation formulas are reported. Finally, an outstanding low pass filtering effect intrinsic to the magnetic response of the system is described.

cond-mat.supr-con↗

arXiv2011

Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution

A self-consistent, mean-field model of charge-carrier injection and unipolar transport in an organic semiconductor diode is developed utilizing the effective transport energy concept and taking into account a realistic density-of-states distribution as well as the presence of trap states in an organic material. The consequences resulting from the model are discussed exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic conductor structure. A comparison of the theory to experimental data of a unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.

cond-mat.mtrl-sci↗

arXiv2010

Charge carrier injection into insulating media: single-particle versus mean-field approach

Self-consistent, mean-field description of charge injection into a dielectric medium is modified to account for discreteness of charge carriers. The improved scheme includes both the Schottky barrier lowering due to the individual image charge and the barrier change due to the field penetration into the injecting electrode that ensures validity of the model at both high and low injection rates including the barrier dominated and the space-charge dominated regimes. Comparison of the theory with experiment on an unipolar ITO/PPV/Au-device is presented.

cond-mat.mtrl-sci↗

arXiv2009

Hysteretic ac losses in a superconductor strip between flat magnetic shields

Hysteretic ac losses in a thin, current-carrying superconductor strip located between two flat magnetic shields of infinite permeability are calculated using Bean's model of the critical state. For the shields oriented parallel to the plane of the strip, penetration of the self-induced magnetic field is enhanced, and the current dependence of the ac loss resembles that in an isolated superconductor slab, whereas for the shields oriented perpendicular to the plane of the strip, penetration of the self-induced magnetic field is impaired, and the current dependence of the ac loss is similar to that in a superconductor strip flanked by two parallel superconducting shields. Thus, hysteretic ac losses can strongly augment or, respectively, wane when the shields approach the strip.

cond-mat.supr-con↗

arXiv2009

Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries

Migration of charged point defects triggered by the local random depolarization field is shown to plausibly explain aging of poled ferroelectric ceramics providing reasonable time and acceptor concentration dependences of the emerging internal bias field. The theory is based on the evaluation of the energy of the local depolarization field caused by mismatch of the polarizations of neighbor grains. The kinetics of charge migration assumes presence of mobile oxygen vacancies in the material due to the intentional or unintentional acceptor doping. Satisfactory agreement of the theory with experiment on the Fe-doped lead zirconate titanate is demonstrated.

cond-mat.mtrl-sci↗

arXiv2008

The Bean model of the critical state in a magnetically shielded superconductor filament

We study the magnetization of a cylindrical type-II superconductor filament covered by a coaxial soft-magnet sheath and exposed to an applied transverse magnetic field. Examining penetration of magnetic flux into the superconductor core of the filament on the basis of the Bean model of the critical state, we find that the presence of a non-hysteretic magnetic sheath can strongly enhance the field of full penetration of magnetic flux. The average magnetization of the superconductor/magnet heterostructure under consideration and hysteresis AC losses in the core of the filament are calculated as well.

cond-mat.supr-con↗

arXiv2008

Bipolar charge-carrier injection in semiconductor/insulator/conductor heterostructures: self-consistent consideration

A self-consistent model of bipolar charge-carrier injection and transport processes in a semiconductor/insulator/conductor system is developed which incorporates space-charge effects in the description of the injection process. The amount of charge-carriers injected is strongly determined by the energy barrier emerging at the contact, but at the same time the electrostatic potential generated by the injected charge-carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and of the electrochemical potential all over the system. The constituents of the system are properly taken into account by means of their respective density of state distributions. The consequences resulting from our model are discussed on the basis of an indium tin oxide/organic semiconductor/conductor structure. The distributions of the charge carriers and the electric field through the electrodes and the organic layer are calculated. The recombination- and current-voltage characteristics are analyzed for different heights of injection barriers and varying values of the recombination rate and compared with the measured current-voltage dependences for an indium tin oxide/poly(phenylene vinylene)/Ca structure. The voltage dependences of the recombination efficiency for the different values of injection barriers and recombination rate reveal optimum conditions for the device performance.

cond-mat.mtrl-sci↗

arXiv2006

Penetration of an external magnetic field into a multistrip superconductor/soft-magnet heterostructure

The magnetization of a planar heterostructure of periodically alternating type-II superconductor and soft-magnet strips exposed to a transverse external magnetic field is studied. An integral equation governing the sheet current distribution in the Meissner state of the superconductor constituents is derived. The field of complete penetration of magnetic flux in the critical state of the superconductor constituents is calculated for different widths of the superconductor and the soft-magnet constituents and a range of values of the relative permeability of the soft-magnet constituents.

cond-mat.supr-con↗

arXiv2005

The Bean-Livingston barrier at a superconductor/magnet interface

The Bean-Livingston barrier at the interface of type-II superconductor/soft-magnet heterostructures is studied on the basis of the classical London approach. This shows a characteristic dependence on the geometry of the particular structure and its interface as well as on the relative permeability of the involved magnetic constituent. The modification of the barrier by the presence of the magnet can be significant, as demonstrated for a cylindrical superconducting filament covered with a coaxial magnetic sheath. Using typical values of the relative permeability, the critical field of first penetration of magnetic flux is predicted to be strongly enhanced, whereas the variation of the average critical current density with the external field is strongly depressed, in accord with the observations of recent experiments.

cond-mat.supr-con↗

arXiv2004

Entry of magnetic flux into a magnetically shielded type-II superconductor filament

In the framework of the London approximation the magnetic flux penetration into a type-II superconductor filament surrounded by a soft-magnet sheath and exposed to a transverse external magnetic field is studied. The lower transverse critical field as well as the critical field and the critical current of the first vortex nucleation at the superconductor/magnet interface are calculated on the basis of an exact solution for a vortex of arbitrary plane configuration. The Bean-Livingston barrier against the vortex nucleation is shown to strongly depend on the magnet sheath parameters.

cond-mat.supr-con↗

arXiv2004

Distribution of the sheet current in a magnetically shielded superconducting filament

The distribution of the transport current in a superconducting filament aligned parallel to the flat surface of a semi-infinite bulk magnet is studied theoretically. An integral equation governing the current distribution in the Meissner state of the filament is derived and solved numerically for various filament-magnet distances and different relative permeabilities. This reveals that the current is depressed on the side of the filament adjacent to the surface of the magnet and enhanced on the averted side. Substantial current redistributions in the filament can already occur for low values of the relative permeability of the magnet, when the distance between the filament and the magnet is short, with evidence of saturation at moderately high values of this quantity, similar to the findings for magnetically shielded strips.

cond-mat.supr-con↗

arXiv2004

Virgin magnetization of a magnetically shielded superconductor wire: theory and experiment

On the basis of exact solutions to the London equation the magnetic moment of a type II superconductor filament surrounded by a soft-magnet environment is calculated and the procedure of extracting the superconductor contribution from magnetic measurements is suggested. Comparison of theoretical results with experiments on MgB_2/Fe wires allows estimation of the value of critical current for the first magnetic flux penetration.

cond-mat.supr-con↗

arXiv2003

Strong reduction of ac losses in a superconductor strip located between superconducting ground plates

The problem of calculating the ac losses in a superconductor strip with a transport current placed inside superconducting environments is studied analytically in the frame of the critical state model. Exact results obtained by the method of images for the commonly employed flat ground plates are used to derive power losses and, consequently, the nonlinear resistance depending on the ac frequency, current amplitude and the distance to the ground plates. The resistance is strongly reduced when the distance between the strip and the shields becomes small.

cond-mat.supr-con↗

arXiv2000

Overcritical states of a superconductor strip in a magnetic environment

A current-carrying superconducting strip partly penetrated by magnetic flux and surrounded by a bulk magnet of high permeability is considered. Two types of samples are studied: those with critical current controlled by an edge barrier dominating over the pinning, and those with high pinning-mediated critical current masking the edge barrier.It is shown for both cases that the current distribution in a central flux-free part of the strip is strongly affected by the actual shape of the magnetic surroundings. Explicit analytical solutions for the sheet current and self-field distributions are obtained which show that, depending on the geometry, the effect may suppress the total loss-free transport current of the strip or enhance it by orders of magnitude. The effect depends strongly on the shape of the magnet and its distance to the superconductor but only weakly on the magnetic permeability.

cond-mat.supr-con↗

arXiv2000

Large Predicted Self-Field Critical Current Enhancements In Superconducting Strips Using Magnetic Screens

A transport current distribution over a wide superconducting sheet is shown to strongly change in a presence of bulk magnetic screens of a soft magnet with a high permeability. Depending on the geometry, the effect may drastically suppress or protect the Meissner state of the sheet through the enhancement or suppression of the edge barrier critical current. The total transport current in the magnetically screened Meissner state is expected to compete with the critical current of the flux-filled sheet only for samples whose critical current is initially essentially controlled by the edge barrier effect.

cond-mat.supr-con↗