Self-heating hotspots in superconducting thin-film microbridges

TLDR

Heating in superconducting thin‑film microbridges can be explained by a localized normal hotspot driven by Joule heating, except near Tc at low voltages where quantum effects dominate. The authors model long, short, and microwave‑coupled bridges using appropriate approximations to capture hotspot behavior. Analytic I‑V expressions derived from the hotspot model match experimental data, explain low‑temperature hysteresis, set a high‑voltage limit for the ac Josephson effect, and quantify heating effects across different weak‑link types.

Abstract

Heating effects in both long and short superconducting thin-film microbridges are described and analyzed. Except near Tc at low voltages where superconducting quantum processes occur, all of our experimental dc I-V characteristics can be satisfactorily understood on the basis of a simple model of a localized normal hotspot maintained by Joule heating. We consider approximations appropriate to the cases of long bridges, short bridges, and bridges coupled to microwave radiation. The analysis leads to analytic expressions for the I-V characteristics which agree well with the experimental data. We show that the formation of such a hotspot is the dominant cause of the hysteresis observed in the I-V characteristics at low temperatures. We also show that the growth of such a hotspot imposes a high-voltage limit on the ac Josephson effect in these devices, and we compare the importance of such heating effects at high voltages in various types of superconducting weak links.