Josephson oscillations and noise temperatures in YBa₂Cu ₃O_7-x grain-boundary junctions

Abstract

The ac Josephson effect was studied in YBa2Cu3O 7-x grain-boundary junctions (GBJ) in the temperature range from 4 to 90 K. The temperature dependence of the linewidth of millimeter-wave Josephson oscillations was measured and it is shown that the derived effective noise temperatures may be as low as the physical temperature in the temperature range investigated. In the millimeter-wave range, linewidths as low as 380 MHz were found at liquid-nitrogen temperatures.