Comment on the "Decrease of the surface resistance in superconducting niobium resonator cavities by the microwave field"

TL;DR

This paper critically examines claims that thermal effects and low-field Q slope are responsible for increased surface resistance in nitrogen-doped niobium superconducting cavities, providing evidence to refute those claims and clarify the underlying mechanisms.

Contribution

It offers a detailed critique of previous interpretations, demonstrating that the observed effects are not due to thermal effects or low-field Q slope, and clarifies the true cause of the surface resistance decrease.

Findings

Thermal effects are not responsible for the observed phenomena.

The increase in Q at 2 K is not just a low-field Q slope.

The decrease in surface resistance is due to other mechanisms, not the BCS component.

Abstract

In a recent publication [Appl. Phys. Lett. 104, 092601 (2014)] Ciovati et al. claim that: 1) thermal effects were disregarded in our original work [*]; 2) increase of $Q$ at $T=2$ K up to about $B\sim$100 mT in nitrogen doped cavities is just an extended low field $Q$ slope observed in non-doped cavities, which is furthermore attributed to the decrease of the "BCS" component of surface resistance. Here we show that both claims are wrong and the conclusions of Ciovati et al. are incorrect. [*] A. Romanenko and A. Grassellino, Appl. Phys. Lett. 102, 252603 (2013)