Observation of Ising-like critical fluctuations in frustrated Josephson junction arrays with modulated coupling energies

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Abstract

We report the results of ac sheet conductance measurements performed on fully frustrated square arrays of Josephson junctions whose coupling energy is periodically modulated in one of the principal lattice directions. Such systems are predicted to exhibit two distinct transitions: a low-temperature Ising-like transition triggered by the proliferation of domain walls and a high-temperature transition driven by the vortex unbinding mechanism of the Beresinskii–Kosterlitz–Thouless (BKT) theory. Both the superfluid and dissipative components of the conductance are found to exhibit features which unambiguously demonstrate the existence of a double transition whose properties are consistent with the Ising-BKT scenario.

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Acknowledgements

We would like to thank S.E. Korshunov for useful discussions. This work was supported by the Swiss National Science Foundation, the Swiss Federal Office for Education and Science within the framework of the TMR network “Superconducting Nanocircuits” of the European Union and the Vortex Program of the European Science Foundation.

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