Observation of the Reverse ac Josephson Effect in Y-Ba-Cu-O at 240 K

Abstract
A two-step resistive transition, one beginning at 240 K and the other at 90 K, has been observed in Y-Ba-Cu-O compounds. The superconductivity, possibly in granular form, at both temperatures has been verified by means of the rf-to-dc conversion associated with the ac Josephson effect.