Showing papers by "Andre K. Geim published in 1999"
TL;DR: In this paper, it was shown that the stable levitation of a magnet can be achieved using the feeble diamagnetism of materials that are normally perceived as being non-magnetic, so that human fingers can keep a magnet hovering in mid-air without touching it.
Abstract: The stable levitation of magnets is forbidden by Earnshaw's theorem, which states that no stationary object made of magnets in a fixed configuration can be held in stable equilibrium by any combination of static magnetic or gravitational forces1,2,3. Earnshaw's theorem can be viewed as a consequence of the Maxwell equations, which do not allow the magnitude of a magnetic field in a free space to possess a maximum, as required for stable equilibrium. Diamagnets (which respond to magnetic fields with mild repulsion) are known to flout the theorem, as their negative susceptibility results in the requirement of a minimum rather than a maximum in the field's magnitude2,3,4. Nevertheless, levitation of a magnet without using superconductors is widely thought to be impossible. We find that the stable levitation of a magnet can be achieved using the feeble diamagnetism of materials that are normally perceived as being non-magnetic, so that even human fingers can keep a magnet hovering in mid-air without touching it.
138 citations
TL;DR: In this article, the authors used the technique of ballistic Hall micromagnetometry to study the annihilation process of an individual domain in sub-micron ferromagnetic nickel disks, which allows to detect changes in magnetization as low as 5×10 4 μ B over a wide range of temperatures.
15 citations
TL;DR: In this article, the authors observed a new discontinuity and bistability in the tunnel current of a 12-nm single-barrier GaAs/AlAs p-i-n heterostructure where a system of spatially separated two-dimensional electron and hole (e-h) layers of equal and tunable density is realized.
Abstract: We observed a new discontinuity and bistability in the tunnel current of a 12-nm single-barrier GaAs/AlAs p-i-n heterostructure where a system of spatially separated two-dimensional electron and hole (e-h) layers of equal and tunable density is realized. Both features appear at T less than or similar to 300 mK and are substantially enhanced in a magnetic field B greater than or similar to 10 T perpendicular to the layers. They correspond to a discontinuity in the e-h density and in the phase of the current magneto-oscillations, which we suggest to arise from a transition between indirect excitons and the uncoupled e-h gases. [S0163-1829(99) 12343-9].
2 citations