Imaging the vortex-lattice melting process in the presence of disorder

• Published in: Nature (London) 2000-07, Vol.406 (6793), p.282-287
• Main Authors: Soibel, Alex, Zeldov, Eli, Rappaport, Michael, Myasoedov, Yuri, Tamegai, Tsuyoshi, Ooi, Shuuichi, Konczykowski, Marcin, Geshkenbein, Vadim B
• Format: Article
• Language: English
• Subjects: Disorders; Engineering Sciences; Fluid flow; Heat; Humanities and Social Sciences; Hysteresis; letter; Mechanics; Melting; multidisciplinary; Nucleation; Physics; Science; Science (multidisciplinary); Superconductivity; Superconductors; Supercooling; Surface tension; Vortices
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/35018532

General arguments suggest that first-order phase transitions become less sharp in the presence of weak disorder, while extensive disorder can transform them into second-order transitions; but the atomic level details of this process are not clear. The vortex lattice in superconductors provides a unique system in which to study the first-order transition on an inter-particle scale, as well as over a wide range of particle densities. Here we use a differential magneto-optical technique to obtain direct experimental visualization of the melting process in a disordered superconductor. The images reveal complex behaviour in nucleation, pattern formation, and solid-liquid interface coarsening and pinning. Although the local melting is found to be first-order, a global rounding of the transition is observed; this results from a disorder-induced broad distribution of local melting temperatures, at scales down to the mesoscopic level. We also resolve local hysteretic supercooling of microscopic liquid domains, a non-equilibrium process that occurs only at selected sites where the disorder-modified melting temperature has a local maximum. By revealing the nucleation process, we are able to experimentally evaluate the solid-liquid surface tension, which we find to be extremely small.