Intrinsic Josephson junction arrays containing only a few junctions

Abstract

After an ordinary mesa is fabricated on a piece of single crystal Bi 2Sr 2CaCu 2O 8+ δ , another ion milling concentrating on the center of the mesa is carried out, resulting in a U-shaped structure with a very thin stack of intrinsic Josephson junctions sitting at its bottom. By using low energy in the milling and reducing the etching rates, we can control the junction number precisely and even a single intrinsic Josephson junction can be fabricated. The I– V characteristics for 4-, 3-, and 1-junction arrays are shown here to support the argument. In the last case (a single junction), some typical structures are believed to be attributable to the behavior of a superconductor–insulator–superconductor (S–I–S) junction with an I c R n product of 7.2 mV at 4.2 K, and a suppressed energy gap structure of Δ=12 meV. Various microwave-induced steps are observed in the frequency range of 1–20 GHz.