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.

Thermal conductivity of high-T c superconductors

“…The authors associate such behavior with trace amounts of a mysterious very high-Tc phase. The latest contribution in this regard is the interesting work of Chen et al [86] on a mixed-phase Y-Ba-Cu-O material that was subjected to a low-temperature (< 150~ oxygenation process. The samples were enclosed in an oxygen atmosphere and electrical and magnetic measurements were performed.…”

Superconductivity above 200 K

“…We have been studying samples with nominal compositions having Ba deficiency, to enable Er or other Y-site cations to occupy the Ba site. It is interesting to note that the nominal composition of 5 : 6 : 11 for Y :Ba:Cu recently used by Chen et a1 [9], which yielded filamentary superconductivity above 200 K, is also essentially deficient in Ba and with a Y surplus. In our case, the observations of unstable partial resistance drops above 200 K were restricted to 5 to 8 of the 40 to 50 samples studied, while the present report represents the only instance with the resistance dropping to zero above 200 K.…”