Showing papers by "Andre K. Geim published in 2001"

Diamagnetically stabilized magnet levitation

Abstract: Stable levitation of one magnet by another with no energy input is usually prohibited by Earnshaw’s theorem. However, the introduction of diamagnetic material at special locations can stabilize such levitation. A magnet can even be stably suspended between (diamagnetic) fingertips. A very simple, surprisingly stable room temperature magnet levitation device is described that works without superconductors and requires absolutely no energy input. Our theory derives the magnetic field conditions necessary for stable levitation in these cases and predicts experimental measurements of the forces remarkably well. New levitation configurations are described which can be stabilized with hollow cylinders of diamagnetic material. Measurements are presented of the diamagnetic properties of several samples of bismuth and graphite.

Detection of earth rotation with a diamagnetically levitating gyroscope

Abstract: Strong magnetic fields allow levitation of apparently nonmagnetic substances due to their weak but not negligible diamagnetic response of about 10−5. Importantly, the diamagnetic force compensates gravity on the level of individual atoms and molecules and, therefore, can be used to mimic a continuous zero-gravity environment that, otherwise, is only achievable on board of a space station. Here we employ this earth-bound low gravity to demonstrate a simple mechanical gyroscope with sensitivity already comparable to that achieved by quantum and military gyroscopes. Our gyroscope can serve as a “shooting range” for the development of precision orbiting gyroscopes that have been a subject of intensive discussions regarding possible tests of general relativity.

Improved conductance quantization in gold point contacts in high magnetic fields

Abstract: We have studied the influence of magnetic field on room-temperature quantization in normal-metal point contacts by measuring the transient conductance during a mechanical break of the electric contact between two macroscopic pieces of Au. It is found that, with increasing the magnetic field parallel to the movement of a sharp tip retracted from a mechanical contact with a large Au plate, the conductance steps become increasingly better defined. We attribute this observation to a micro-mechanical force caused by magnetic field and acting on the atomic wires drawn by the tip at the final stages of the breaking process.