Physikalisches Institut

Intrinisic Josephson effect

High-transition-temperature superconductors such as the compound Bi2Sr2CaCu2O8 (BSCCO) have a layered structure. Here the copper oxide planes, which are responsible for superconductivity in these compounds, are separated by non-superconducting barrier layers (SrO and Bi2O3 in the case of BSCCO). Hence, these systems form intrinsic stacks of Josephson juntions, where the thickness of a single juntion is only approx. 1.5 nm (the layer sequence CuO2-SrO/ Bi2O3-CuO2 forms here an intrinsic junction). A 1 µm thick BSCCO single crystal consists of a stack of 666 of these junctions. Intrinsic Josephson junctions can oscillate at frequencies up to above 10 Terahertz. They are therefore of great importance, e.g. for the generation of electromagnetic radiation in particular in the terahertz regime.

The intrinsic Josephson effect was discovered in 1992 by R. Kleiner and P. Müller, and is intensively investigated worldwide.

Fig.1 : Schematic representation of intrinsic Josephson junctions in Bi2Sr2CaCu2O8, togehter with the crystal structure of the material (left). The blue layers represent the superconducting layers (CuO2 layers), the transparent layers inbetween are the insulating barriers. The graph at the right shows part of a typical current-voltage-characteristic (IVC). The Josephson junctions in the stack can be switched individually between the zero-voltage and the resistive state. Hence, the IVC consists of many branches, which differ by the number of resistive junctions. In the figure, three of these branches are shown. The arrows indicate the direction of current ramp which was used to record the IVC.

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