arXiv subjects

V. V. Moshchalkov

Publications and source records attributed to V. V. Moshchalkov.

131 records · Page 8Linked to original sources

arXiv1998

Vortex configurations in a Pb/Cu microdot with a 2x2 antidot cluster

We present a detailed study of the transport properties of a superconducting Pb/Cu microdot with a 2x2 antidot cluster. The superconducting-normal (S/N) phase boundary, critical currents and current-voltage characteristics of this structure have been measured. The S/N phase boundary as a function of field B (T_c(B)) reveals an oscillatory structure caused by the limited number of possible vortex configurations which can be realized in these small clusters of pinning centres (antidots). We have analyzed the stability of these configurations and discussed the possible dissipation mechanisms using the critical current (J_c(B)) and voltage-current (V(I)) characteristics data. A comparison of the experimental data of T_c(B) and J_c(B) with calculations in the London limit of the Ginzburg-Landau theory confirms that vortices can indeed be pinned by the antidots forming a cluster and that the ground-state configurations of the vortices are noticeably modified by sending current through the structure. The possibility of generating phase-slips as well as motion of the vortices in the 2x2 antidot cluster has also been discussed.

cond-mat.supr-con↗

arXiv1998

Confinement and Quantization Effects in Mesoscopic Superconducting Structures

We have studied quantization and confinement effects in nanostructured superconductors. Three different types of nanostructured samples were investigated: individual structures (line, loop, dot), 1-dimensional (1D) clusters of loops and 2D clusters of antidots, and finally large lattices of antidots. Hereby, a crossover from individual elementary "plaquettes", via clusters, to huge arrays of these elements, is realized. The main idea of our study was to vary the boundary conditions for confinement of the superconducting condensate by taking samples of different topology and, through that, modifying the lowest Landau level E_LLL(H). Since the critical temperature versus applied magnetic field T_c(H) is, in fact, E_LLL(H) measured in temperature units, it is varied as well when the sample topology is changed through nanostructuring. We demonstrate that in all studied nanostructured superconductors the shape of the T_c(H) phase boundary is determined by the confinement topology in a unique way.

cond-mat.supr-con↗

arXiv1998

Crossover from the 2D Heisenberg to the 1D Quantum Spin Ladder Regime in Underdoped High Tc Cuprates

The enigmatic scaling behaviour of the normal state properties of the high Tc cuprates has been explained by assuming that a crossover from the two- dimensional Heisenberg (2D-H) to the one-dimensional spin ladder (1D-SL) regime takes place at temperature T=T*. For T T* the 2D quantum transport is realized with L_ϕgoverned by the 2D-H correlations L_phi=xi_m=exp(J/T)$. Therefore, the pseudogap found in underdoped (p<p_opt) high Tc's is the spin-gap Delta(p) in even-chain 1D-SL.

cond-mat.supr-con↗

arXiv1998

Crossovers Between Elastic, Plastic and Quantum Creep in Two Dimensional YBa_2Cu_3O_7/PrBa_2Cu_3O_7 Superlattices

Two-dimensional(2D) vortex dynamics was studied in an YBa_2Cu_3O_7/ PrBa_2Cu_3O_7 superlattice by measuring the I-V characteristics. In the high current limit, 2D collective creep was observed with an activation energy characterized by U(j)=a j^u. A dislocation mediated vortex melting happened when the temperature increased. In the low current limit, the exponential growth of energy barrier for elastic motion was prohibited by the plastic deformation of vortices. A plateau in the resistive transition was observed, which was attributed to possible quantum tunneling of vortices. Our results suggest that a 2D vortex glass can not exist at any temperature, including T=0 K.

cond-mat.supr-con↗

arXiv1998

Vortex Lattice Melting into Disentangled Liquid Followed by the 3D-2D Decoupling Transition in YBa_2Cu_4O_8 Single Crystals

A sharp resistance drop associated with vortex lattice melting was observed in high quality YBa_2Cu_4O_8 single crystals. The melting line is well described well by the anisotropic GL theory. Two thermally activated flux flow regions, which were separated by a crossover line B_cr=1406.5(1-T/T_c)/T (T_c=79.0 K, B_cr in T), were observed in the vortex liquid phase. Activation energy for each region was obtained and the corresponding dissipation mechanism was discussed. Our results suggest that the vortex lattice in YBa_2Cu_4O_8 single crystal melts into disentangled liquid, which then undergoes a 3D-2D decoupling transition.

cond-mat.supr-con↗