• Eom, Chang-Beom
• Su, Yi-Feng
• Sundahl, Chris
• Makita, Junki
• Kametani, Fumitake
• Zhang, Huimin
• Welander, Paul B.
• Li, Lian
• Gurevich, Alex
• Xie, Lin

Abstract

Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors > 10¹⁰ at 1–2 GHz and 2 K in large linear accelerators of high-energy particles. The maximum accelerating field of SRF cavities is limited by penetration of vortices into the superconductor. Present state-of-the-art Nb cavities can withstand up to 50 MV/m accelerating gradients and magnetic fields of 200–240 mT which destroy the low-dissipative Meissner state. Achieving higher accelerating gradients requires superconductors with higher thermodynamic critical fields, of which Nb3Sn has emerged as a leading material for the next generation accelerators. To overcome the problem of low vortex penetration field in Nb₃Sn, it has been proposed to coat Nb cavities with thin film Nb₃Sn multilayers with dielectric interlayers. Here, we report the growth and multi-technique characterization of stoichiometric Nb₃Sn/Al₂O3 multilayers with good superconducting and RF properties. We developed an adsorption-controlled growth process by co-sputtering Nb and Sn at high temperatures with a high overpressure of Sn. The cross-sectional scanning electron transmission microscope images show no interdiffusion between Al₂O₃ and Nb₃Sn. Low-field RF measurements suggest that our multilayers have quality factor comparable with cavity-grade Nb at 4.2 K. These results provide a materials platform for the development and optimization of high-performance SIS multilayers which could overcome the intrinsic limits of the Nb cavity technology.

Topics

• impedance spectroscopy
• thin film
• interdiffusion