Low-temperature scanning electron microscopy of temperature structures in superconducting bridges

Abstract

Temperature structures generated in a thin-film superconducting bridge through dissipation of Joule energy can be imaged by low-temperature scanning electron microscopy (LTSEM). Two voltage peaks are obtained at the boundaries of the hotspot, where the temperature profile passes through the critical temperatureT _c of the bridge. If the electron beam is modulated at high frequencies the width of the modulated voltage peaks is about twice the dynamic thermal healing length and decreases with increasing modulation frequency. In this way, the spatial resolution of LTSEM can be increased considerably. Experiments performed with an O₂-doped Sn bridge up to beam modulation frequencies of 10 MHz confirm these effects. They are in good agreement with all predictions from a theoretical analysis in which the electron beam irradiation is treated as a small thermal perturbation of the sample.