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States of matter

States of matter

Magnetic vortices defy melting moment

01 Aug 2001

The discovery of high-temperature superconductors has stimulated a remarkable growth in our understanding of the physics of magnetic vortices – tubes of flux that are created when a magnetic field above a certain critical field penetrates such materials. Recent studies of these vortices have produced some surprising results – and physicists are learning just how rich the phase diagram of vortex matter can be.

The behaviour of magnetic vortices controls many physical properties of high-temperature superconductors, including their ability to carry current without resistance – a classic hallmark of superconductivity.

Indeed, vortices provide an ideal platform for the creation and study of novel phases and phase transitions. Now Nurit Avraham at the Weizmann Institute in Israel and co-workers from Russia, Japan, France and the Netherlands have observed a rare phase transition known as “inverse melting” in a magnetic-vortex system for the first time. Meanwhile a collaboration of French, Swiss and US scientists has uncovered a new second-order phase transition between two liquid vortex states in a superconducting yttrium-barium-copper-oxide compound (Nature 2001 411 451; 448).

In the August issue of Physics World, Wai-Kwong Kwok of Argonne National Laboratory, USA, explores the new effects.

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