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Fortunately enough, a high resistance does not make a superconducting Josephson junction insulating!

​Researchers from CEA-Iramis and their partners refute a widely accepted assertion that the coupling of a Josephson junction to a high resistance is constrained.  They thus open the way to new high-impedance devices, previously considered unfeasible.

Published on 11 March 2021

In 1962, Brian David Josephson predicted that an electric current could flow, without applied voltage, through a thin insulating layer separating two superconductors:  The Josephson Junction was invented.  It is used today in many quantum electronic devices:  Magnetometers, parametric amplifiers, logic circuits, superconducting quantum bits, etc.

In 1983, Albert Schmid predicted that any Josephson Junction shunted by a high electrical resistance should not be superconducting but insulating.  This assertion is however paradoxical because if the resistance becomes infinite, no Josephson Junction should be superconducting!  Despite this theoretical inconsistency, it seemed to be confirmed by several experiments performed in the 1990s and was considered established by the scientific community.

Physicists from Iramis and German academics demonstrate that the insulating state predicted by Albert Schmid does not exist.

Their rigorous characterization of Josephson Junctions connected to resistances above the threshold value predicted by Albert Schmid reveals a linear response that "saturates" at low temperatures but unambiguously retains a superconducting character.  Beyond this experimental observation, they explain that due to a subtle topological difference, Albert Schmid's prediction does not apply to the coupling of a superconducting system (such as a Josephson Junction) to a resistor.

By resolving a theoretical inconsistency and providing a complete understanding of the interaction of Josephson junctions with their electrical environment, this work opens a way to a new high impedance superconducting devices using Josephson Junctions... that were previously considered unfeasible.

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