Seminars & Colloquia

Electrical polarity in nanosystems

Philip B. Allen
SUNY, Stony Brook

Wednesday, April 7, 2004
4:00 pm, Higgins 310
Refreshments precede the talk, Higgins 230, 3:30 pm

Electrical dipoles have curious properties. Their fields wrap back, fall as R-3, and are usually screened so as to be invisible at any decent distance. At short-range, their fields are enormous, yet they are less familiar than their weak but poorly screened magnetic cousins. When dipole-dipole interactions dominate, curious patterns of ordering occur. I will argue that the "tilted" phases of octahedrally coordinated ions (perovskite crystals, high Tc superconductors, etc.) are a manifestation. On the nanoscale, little is known. Unexpected spontaneous dipoles have been reported on metal clusters (2 to 200 atoms). On ionic clusters, spontaneous dipoles may occur, and intrinsic dipoles from cluster geometry are often to be expected, but they have been seldom seen or discussed. Some theoretical considerations, calculations, and speculations will be given.