OBSERVATION OF THERMALLY RECYCLEABLE ZERO-RESISTANCE STATES IN YBaCuO ABOVE DRY ICE TEMPERATURES

Abstract

Thermally recycleable zero-resistance states with transition temperatures above 200 K are observed in mixed-phase YBaCuO materials that are treated by a low-temperature (< 150° C ) oxygenation process and enclosed in an oxygen atmosphere during electrical and magnetic measurements. The zero-resistance state is verified through multiple lead and contact arrangements as well as by measurements of the current-voltage characteristics for several paths with the highest transition temperature (zero resistance) for any sample being 265 K and with a zero-voltage current exceeding 4.3 mA at 240 K. Although a full Meissner effect is not obtained, diamagnetic-like deviations and hysteretic behavior are observed to occur at the same temperatures as the resistive transitions. This indicates that the zero resistance, if related to superconductivity, is due to filamentary superconducting paths or materials of lower dimensionality.