Practical way to increase nonlinearity of kinetic inductance of superconductor

Superconductor Science and Technology. 2025. Vol. 38. No. 7. Article 075016.

Korneeva Y. P., Dryazgov M. A., Trofimov I. V., Levichev M. Y., Porokhov N. V., Mumlyakov A. M., Shibalov M. V., A. A. Korneev

This work demonstrates that depositing a thin layer of Mo (5–15 nm) onto a 10 nm thick NbN strip leads to a significant increase in the nonlinearity of the kinetic inductance . Specifically, the change in  with increasing current reached 70% in the NbN/Mo bilayer at liquid helium temperature, whereas in the NbN strip,  changed by only 10% in the superconducting state. In addition to altering the nonlinear properties, the Mo layer caused a significant increase in the critical current at low temperatures (up to 2 times in the case of a 5 nm thick Mo layer). The increased nonlinearity of  can be explained by two factors: (i) a reduction of the critical supervelocity at which the superconducting state becomes unstable when a Mo layer is deposited on NbN, and (ii) a higher sensitivity of the induced superconductivity in Mo to supervelocity/supercurrent. Considering the results on the transport properties of SN bilayers with a high ratio of layer resistivities , it can be concluded that depositing a thin layer of a relatively low-resistivity metal onto a superconductor with high  is a practical method for achieving a large nonlinearity of the superconductor’s kinetic inductance.

Keywords: proximity effect, эффект близости, superconducting films, сверхпроводящие тонкие плёнки, superconductor normal metal bilayer nonlinear kinetic inductance, нелинейная кинетическая индуктивность