Physics 1973 Current in microamperes Fig 3. The first published observation of tunnelling between two evaporated- film supe nductors(Nicol, Shapiro and ference 6). A zero-voltage supercurrent is clearly visible. It was not until th tents of Anderson and Rowell(reference 15) that such supercurrents could be ascribed to the tunnelling process specimens to produce a current exceeding the critical current. Together with John Rowell he made some low resistance specimens and soon obtained vincing evidence(15)for the existence of tunnelling supercurrents, shown particularly by the sensitivity to magnetic fields, which would not be present in the case of conduction through a metallic short. In one specimen they found a critical current of 0.30 n the Earth's magnetic field. When the ted, the critical current increased by more than a factor of two,to 0.65 mA, while a field of 2mT was sufficient to destroy the zero- voltage supercurrents completely. Later Rowell (16) investigated the field de- pendence of the critical current in detail, and obtained results related to the diffraction pattern of a single slit, a connection first suggested by J. C. Phillips (unpublished). This work was advanced by Jaklevic, Lambe, Silver and Mer cereal,(17) who connected two junctions in parallel and were able to observe the analogue of the Youngs slit interference experiment. The sensitivity of the critical current to applied magnetic field can be increased by increasing the area enclosed between the two branches of the circuit, and Zimmerman and Silver(18) were able to achieve a sensitivity of 10"T Indirect evidence for the ac supercurrents come soon after. Shapiro(19) none microwaves on to a junction and observed the predicted appearance at which the steps occurred changed as the frequency of the microwaves was changed, in the manner expected. In 1966, Langenberg Parker and Taylor(20) measuredPhysics 1973 Fig. 3. The first published observation of tunnelling between two evaporated-film super￾conductors (Nicol, Shapiro and Smith, reference 6). A zero-voltage supercurrent is clearly visible. It was not until the experiments of Anderson and Rowe11 (reference 15) that such supercurrents could be definitely ascribed to the tunnelling process. specimens to produce a current exceeding the critical current. Together with John Rowell he made some low resistance specimens and soon obtained con￾vincing evidence (15) for the existence of tunnelling supercurrents, shown particularly by the sensitivity to magnetic fields, which would not be present in the case of conduction through a metallic short. In one specimen they found a critical current of 0.30 mA in the Earth’s magnetic field. When the field was compensated, the critical current increased by more than a factor of two, to 0.65 mA, while a field of 2mT was sufficient to destroy the zero￾voltage supercurrents completely. Later Rowell (16) investigated the field de￾pendence of the critical current in detail, and obtained results related to the diffraction pattern of a single slit, a connection first suggested by J. C. Phillips (unpublished). This work was advanced by Jaklevic, Lambe, Silver and Mer￾cereau, (17) who connected two junctions in parallel and were able to observe the analogue of the Young’s slit interference experiment. The sensitivity of the critical current to applied magnetic field can be increased by increasing the area enclosed between the two branches of the circuit, and Zimmerman and Silver (18) were able to achieve a sensitivity of 10-13 T. Indirect evidence for the ac supercurrents come soon after. Shapiro (19) shone microwaves on to a junction and observed the predicted appearance of steps in the current-voltage characteristics. The voltages at which the steps occurred changed as the frequency of the microwaves was changed, in the manner expected. In 1966, Langenberg, Parker and Taylor (20) measured