Showing papers by "Kostya S. Novoselov published in 2000"
TL;DR: The amount of flux introduced by individual vortices in a superconducting film is measured, finding that the flux always differs substantially from φ0, and ‘negative vortice’ are observed, whose penetration leads to the expulsion of magnetic field.
Abstract: As first pointed out by Bardeen and Ginzburg in the early sixties1,2, the amount of magnetic flux carried by vortices in superconducting materials depends on their distance from the sample edge, and can be smaller than one flux quantum, φ0 = h/2e (where h is Planck's constant and e is the electronic charge). In bulk superconductors, this reduction of flux becomes negligible at sub-micrometre distances from the edge, but in thin films the effect may survive much farther into the material3,4. But the effect has not been observed experimentally, and it is often assumed that magnetic field enters type II superconductors in units of φ0. Here we measure the amount of flux introduced by individual vortices in a superconducting film, finding that the flux always differs substantially from φ0. We have observed vortices that carry as little as 0.001φ0, as well as ‘negative vortices’, whose penetration leads to the expulsion of magnetic field. We distinguish two phenomena responsible for non-quantized flux penetration: the finite-size effect1,2,3,4 and a nonlinear screening of the magnetic field due to the presence of a surface barrier. The latter effect has not been considered previously, but is likely to cause non-quantized penetration in most cases.
142 citations
TL;DR: In this article, the authors report measurements of the amount of flux associated with the entrance of individual vortices in a superconducting film and show that the flux that they bring in, always differs substantially from f0.
Abstract: As first pointed out by Bardeen and Ginzburg in the early sixties, the amount of magnetic flux carried by vortices depends on their distance to the sample edge and can be smaller than one flux quantum, f0 = h/2e. In bulk superconductors, this reduction of flux becomes negligible already at submicron distances from the edge but, in thin films, the effect may survive at much larger distances. In the absence of any experimental observation, such flux reduction is perceived to be an exotic or unimportant effect, and it is often assumed that magnetic field enters type-II superconductors in units of f0. Here we report the measurements of the amount of flux associated with the entrance of individual vortices in a superconducting film and show that the flux that they bring in, always differs substantially from f0. We have observed vortices that carry as little as 0.001 f0 as well as seemingly "negative vortices" whose penetration leads to the expulsion of magnetic field. We distinguish two phenomena responsible for non-quantized flux penetration: the finite-size effect and a non-linear screening of magnetic field in the presence of a surface barrier. The latter effect has previously not been considered but is likely to cause non-quantized penetration in many cases.
134 citations
TL;DR: In this article, the authors studied the transport of 2D electrons through individual magnetic inhomogeneities of the height up to 1 T and the size down to 100 nm and reported an inversion of the sign of the Hall effect.
Abstract: We have studied transport of 2D electrons through individual magnetic inhomogeneities of the height up to 1 T and the size down to 100 nm. Such magnetic fields were created by placing dysprosium microtablets on top of a near-surface 2D electron gas (2DEG). The cyclotron orbit for such inhomogeneities becomes smaller than their size and incident electrons are strongly deflected. We report an inversion of the sign of the Hall effect: a positively magnetised micromagnet on top of a 2DEG gives rise to a Hall signal which corresponds to a negative field applied to the 2DEG. This dramatic anomaly is attributed to the fact that 2D electrons are not able to reach the central, strongest part of the magnetic field and, therefore, the dominant contribution to the Hall effect comes from a stray field having the opposite sign.
10 citations
TL;DR: In this article, the authors studied nonlinear electron transport in normally pinched-off quantum wires and found that the differential conductance of the open wires was noticeably lower than e2/h as far as only part of the source-drain voltage dropped between source contact and saddle point of the potential relief along the wire.
Abstract: Nonlinear electron transport in normally pinched-off quantum wires was studied. The wires were fabricated from AlGaAs/GaAs heterostructures with high-mobility two-dimensional electron gas by electron beam lithography and following wet etching. At certain critical source-drain voltage the samples exhibited a step rise of the conductance. The differential conductance of the open wires was noticeably lower than e2/h as far as only part of the source-drain voltage dropped between source contact and saddle point of the potential relief along the wire. The latter limited the electron flow injected to the wire. At high enough source-drain voltages the decrease of the differential conductance due to the real space transfer of electrons from the wire in GaAs to the doped AlGaAs layer was found. In this regime the sign of the differential magnetoconductance was changed with reversing the direction of the current in the wire or the magnetic field, when the magnetic field lies in the heterostructure plane and is directed perpendicular to the current. The dependence of the differential conductance on the magnetic field and its direction indicated that the real space transfer events were mainly mediated by the interface scattering.
6 citations