Northwestern Events Calendar

May
18
2017

Alexander Gurevich: Ultralow-dissipative superconductivity under strong RF fields

When: Thursday, May 18, 2017
4:00 PM - 5:00 PM CT

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Public - Post Docs/Docs - Graduate Students

Contact: Tina Hoff  

Group: Physics and Astronomy Condensed Matter Physics Seminars

Category: Academic

Description:

Title: Ultralow-dissipative superconductivity under strong RF fields

Speaker: Alexander Gurevich, Old Dominion University

Abstract: Recent technological advances in superconducting Nb resonator cavities for particle accelerators have resulted in the accelerating electric fields up to 50 MV/m at unprecedented quality factors Q(H) up to 1011 @ 2K and 1-2 GHz. Moreover, the resonant cavity geometry offers a unique opportunity to probe such fundamental issues as the lower limits of RF dissipation and surface resistance, and the physics of nonequilibrium superconductivity under strong RF current densities close the depairing limit at which the Meissner state becomes unstable with respect to penetration of vortices. In this talk I will outline the fundamentals of the BCS surface resistance Rs, particularly the reduction of Rs by optimizing the subgap states and broadening the gap peaks in the quasiparticle density of states by materials disorder, and the effect of microwave suppression of the surface resistance by strong RF fields. These issues are essential for understanding the anomalous increase of Q(H) with the RF field which has been observed on Ti or N-treated Nb cavities at JLab, FNAL and Cornell. Possibilities of significant increase of Q(H) by impurity management at the surface and by multilayer nanostructuring with new SRF materials, for instance, Nb3Sn, MgB2 or iron pnictides are discussed. Addressing the fundamental physics and materials science of a 100 nm thick surface layer of RF field penetration can bring new ways of decreasing the surface resistance by optimizing materials disorder and peaks in the quasiparticle density of states while, dealing with the materials defects which can turn their behavior from beneficial to benign and to deadly, depending on the heat treatment of impurity management. These issues can be essential in applications of superconducting microresonators for quantum computing.

Host: James Sauls

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