Single Cooper-pair tunneling junctions using high-Tc superconducting materials

The authors introduce the single electron (Cooper-pair) tunneling junctions using c-axis Bi2Sr2CaCu2O8+d (Bi-2212) superconducting single crystal whiskers. Focused-ion-beam (FIB) etching patterned the Bi-2212 whiskers. The fabricated small stacked junctions have in-plane area S smaller than <1 microm2. The junctions showed the current-voltage (I-V) characteristics with the periodic structure of current peaks. The stacking layered structure of Bi-2212 works as multi-junctions array which decrease the effective capacitance, CΣ = C0/N, where C0 is the capacitance of junction and N is the layer number of elementary junctions. The period of current peaks of I-V curves corresponds to the charging energy of the single Cooper pair, 2Ec (=e2/CΣ)