arXiv subjects

S. V. Yampolskii

Publications and source records attributed to S. V. Yampolskii.

23 records · Page 2Linked to original sources

arXiv2001

Multi-vortex states of a thin superconducting disk in a step-like external magnetic field

The vortex states in a thin mesoscopic disk are investigated within the phenomenological Ginzburg-Landau theory in the presence of a step-like external magnetic field with zero average which could model the field resulting from a ferromagnetic disk or a current carrying loop. The regions of existence of the multi-vortex state and the giant vortex state are found. We analyzed the phase transitions between them and found regions in which ring-shaped vortices contribute. Furthermore, we found a vortex state consisting of a central giant vortex surrounded by a collection of anti-vortices that are located in a ring around this giant vortex.

cond-mat.supr-con↗

arXiv2001

Giant vortices in small mesoscopic disks: an approximate description

We present an approximate description of the giant vortex state in a thin mesoscopic superconducting disk within the phenomenological Ginzburg-Landau approach. Analytical asymptotic expressions for the energies of the states with fixed vorticity are obtained when a small magnetic flux is accumulated in the disk. The spectrum of the lowest Landau levels of such a disk is also discussed.

cond-mat.supr-con↗

arXiv2001

Vortex structure of thin mesoscopic disks in the presence of an inhomogeneous magnetic field

The vortex states in a thin mesoscopic disk are investigated within the phenomenological Ginzburg-Landau theory in the presence of different ''model'' magnetic field profiles with zero average field which may result from a ferromagnetic disk or circulating currents in a loop near the superconductor. We calculated the dependences of both the ground and metastable states on the magnitude and shape of the magnetic field profile for different values of the order parameter angular moment, i.e. the vorticity. The regions of existence of the multi-vortex state and the giant vortex state are found. We analysed the phase transitions between these states and studied the contribution from ring-shaped vortices. A new transition between different multi-vortex configurations as the ground state is found. Furthermore, we found a vortex state consisting of a central giant vortex surrounded by a collection of anti-vortices which are located in a ring around this giant vortex. The limit to a disk with an infinite radius, i.e. a film, will also be discussed. We also extended our results to ''real'' magnetic field profiles and to the case in which an external homogeneous magnetic field is present.

cond-mat.supr-con↗

arXiv2001

Superconducting properties of mesoscopic cylinders with enhanced surface superconductivity

The superconducting state of an infinitely long superconducting cylinder surrounded by a medium which enhances its superconductivity near the boundary is studied within the nonlinear Ginzburg-Landau theory. This enhancement can be due to the proximity of another superconductor or due to surface treatment. Quantities like the free energy, the magnetization and the Cooper-pair density are calculated. Phase diagrams are obtained to investigate how the critical field and the critical temperature depend on this surface enhancement for different values of the Ginzburg-Landau parameter κ. Increasing the superconductivity near the surface leads to higher critical fields and critical temperatures. For small cylinder diameters only giant vortex states nucleate, while for larger cylinders multivortices can nucleate. The stability of these multivortex states also depends on the surface enhancement. For type-I superconductors we found the remarkable result that for a range of values of the surface extrapolation length the superconductor can transit from the Meissner state into superconducting states with vorticity L > 1. Such a behaviour is not found for the case of large κ, i.e. type-II superconductivity.

cond-mat.supr-con↗

arXiv2000

Vortex charge in mesoscopic superconductors

The electric charge density in mesoscopic superconductors with circular symmetry, i.e. disks and cylinders, is studied within the phenomenological Ginzburg-Landau approach. We found that even in the Meissner state there is a charge redistribution in the sample which makes the sample edge become negatively charged. In the vortex state there is a competition between this Meissner charge and the vortex charge which may change the polarity of the charge at the sample edge with increasing magnetic field. It is shown analytically that in spite of the charge redistribution the mesoscopic sample as a whole remains electrically neutral.

cond-mat.supr-con↗