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TT: Fachverband Tiefe Temperaturen

TT 76: Superconductivity: Tunnelling and Josephson Junctions II

TT 76.7: Talk

Thursday, March 21, 2024, 16:45–17:00, H 3010

Fermionic versus bosonic description of dissipation in Josephson junctions — •Oleksiy Kashuba, Theodoulos A. Costi, and Roman-P. Riwar — Peter Grünberg Institute, Theoretical Nanoelectronics, Forschungszentrum Jülich, D-52425 Jülich

The Caldeira-Leggett model is the commonly accepted go-to approach to describe dissipation in superconducting circuits [1]. However, this model predicts a superconductor-insulator transition whose experimental verification is still heavily debated. Starting with the microscopic picture of a Josephson junction coupled to a normal metal, we notice that it matters whether the limit of large superconducting gap is taken before or after the wideband limit (where bosonization applies). For the former, the interaction cannot be mapped exactly to the Caldeira-Leggett model [2]. Instead, we find a generalized Kondo model, which, for large charging energies, reduces to the standard anisotropic Kondo model. While this model features a phase transition of its own, the parameters that control the transition are different. In particular, the phase transition can only occur if the partial capacitance between the superconducting island and normal metal is allowed to be negative. In the same fashion, Langevin equation for quantum phase derived directly from the microscopic model has additional contributions to the ohmic term compared to the Caldeira-Leggett model. Our work thus indicates that different microscopic realizations of the bath may give rise to different phase diagrams.

[1] F. Guinea, V. Hakim, A. Muramatsu, Phys. Rev. Lett. 54 (1985) 263

[2] G. Schön, A. Zaikin, Phys. Reports 198 (1990) 237

Keywords: Caldeira-Leggett model; superconductor-insulator transition; dissipation