Intrinsic Josephson junctions of Tl 2Ba 2CaCu 2O x thin films for high frequency devices

Abstract

We successfully observed intrinsic Josephson effects of Tl 2Ba 2CaCu 2O x (Tl-2212) thin films by structuring step-edges or mesas and measuring the electrical transport properties along the c-axis. For a step-edge with the height of 350 nm, a hysteretic current-voltage ( I– V) curve was observed up to 50 K. For a 5 μ m x 5μ m mesa structure with a height of 400 nm, a hysteretic I– V curve was also observed up to 80 K. Both show that series connected SIS-type junctions are formed. Comparing with the critical current density ( J c) of more than 10 6 A/cm 2 parallel to the ab-plane, an anisotropic J c of 1.4 × 10 2 A/cm 2 at 4.9 K was observed. The normal resistance ( R n k ) of a unit SIS junction was estimated to be 580 Ω by fitting the Ambegaokar and Baratoff relation. The capacitance ( C k ) of the unit SIS junction was estimated to be 3.6 × 10 −10 F/cm 2 at 77 K by the calculation of McCumber parameter (β c). Then, the cut-of frequency 1 2πR nkC k was estimated to be 3.1 THz at 77 K as a THz detector.