High-Frequency Resistance of Superconductors

Abstract

MEASUREMENTS by H. London¹ on the heating of superconducting tin by high-frequency electromagnetic fields indicate the presence in the superconductor of some mechanism which enables it to absorb a measurable quantity of energy from the field provided the frequency is of the order of 1,000 Mc./sec. or more. Recent developments in radio technique have made it possible to employ a resonance method to investigate the effect, and this communication describes preliminary work at frequencies around 1,200 Mc./sec., corresponding to a free-space wave-length of 25 cm. The specimens were polycrystalline thin wires contained in quartz capillary tubes for rigidity, bent into a narrow U to form a twin transmission line roughly a quarter wave-length long, and surrounded, to eliminate radiation losses, by a cylindrical sheath, which was either silver-plated or lined with lead-foil to minimize resistive losses. Measurements of the width of the resonance curve of the system by a controlled variation of the oscillator frequency gave a value for the skin resistance of the specimen.