CRITICAL AND NONCRITICAL BEHAVIOR OF THE KOSTERLITZ-THOULESS-BEREZINSKII TRANSITION

The standard treatment of the Kosterlitz-Thouless-Berezinskii (KTB) tr ansition is supplemented here by the inclusion of free-vortex screenin g effects. We obtain the high-density corrections to the KTB critical behavior. The size of the KTB critical region is extracted, and is fou nd in most cases to be quite small. The tricritical point, separating second-order (KTB) phase transitions from first-order transitions, is also determined. We make predictions concerning similar KTB-like trans itions, such as in the layered cuprate superconductors.