Oak Ridge National Laboratory Review
Volume 30, Numbers 3 & 4, 1997
Color visualizations are among the most intriguing products of high-performance computing, including the efforts at ORNL that are featured in this special issue. The cover image, dubbed the blue tornado, shows the vortex state in a superconductor. The vortex state arises when a magnetic field, which is deleterious to superconductivity, penetrates a superconductor by creating normal (nonsuperconducting) regions. Although the existence of the vortex state was suggested from a phenomenological theory and confirmed by experiment in the 1950s, it had not been studied from the full microscopic theory of superconductivity Such a study was made possible by use of the Intel XP/S 5 and XP/S 3 supercomputers shortly after they arrived at ORNL. The illustration shows how the various quantities that describe the vortex state vary in the neighborhood of a superconducting vortex. The solution is for a two-dimensional regular periodic lattice relevant to high-temperature superconductors such as yttrium-barium-copper oxide. On the lower surface, circulating currents are indicated by arrows while the color encodes the degree to which the magnetic field has penetrated the superconductor. The upper surface shows the variation of the superconducting order parameter. This quantity, which is a complex number, is represented by its magnitude and phase. The height of the upper surface represents the size (magnitude) of the order parameter while the color encodes the phase, which varies from zero (blue) to two-pi (red) as the vortex is encircled. The inverted cone shows the core of the vortex where the magnitude of the order parameter plummets to zero and superconductivity is lost, and where the magnetic field reaches its maximum (red) value. This work was performed by Paul Miller, a research student of Professor B. L. Gyorffy of Bristol University in the United Kingdom, during a visit to ORNL to work with Malcolm Stocks of ORNL's Metals and Ceramics Division.
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