Electromagnetic properties of the Dayem bridge

Abstract

The first measurements on the Dayem bridge showed that the behaviour in an applied microwave field was quite different from that of the Josephson tunnel junction. Measurements on bridges one magnitude smaller later showed this difference to result from the bridge size. A very simple equivalent circuit was furthermore shown to characterize these small bridges. Analog computer calculations on this circuit will be compared to experimental results. At high temperatures a rounding of steps and supercurrent presumably due to noise is observed. A comparison with the theory of Ambegaokar and Halperin will be presented. At low temperatures a hysteresis develops. This may result from the bridge capacitance which also may give rise to subharmonic steps. However, the magnitude (1 pF) inferred from the hysteresis is too small to account for the subharmonic steps actually observed. In contrast to other types of junctions the bridge is mechanically very robust. We have therefore been interested in the applicability of the bridge. An upper limit to the sensitivity to 10 GHz radiation has been found in terms of NEP to 9 × 10-14 W/√Hz. Furthermore, we have demonstrated that mixing via the Josephson effect is possible. The power dependence of the sum and difference steps is in fair agreement with analog computer calculations on the equivalent circuit. It has been debated whether the bridge radiates at all. By the observation of a cavity induced step we have now established that bridges do radiate.