'Inverse' melting of a vortex lattice |
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Authors: | Avraham N Khaykovich B Myasoedov Y Rappaport M Shtrikman H Feldman D E Tamegai T Kes P H Li M Konczykowski M van der Beek K Zeldov E |
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Affiliation: | Department of Condensed Matter Physics, The Weizmann Institute of Science, Rehovot 76100, Israel. nurit.avraham@weizmann.ac.il |
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Abstract: | Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases. Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures. |
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