Harmonic generation from YBCO microwave resonators

TL;DR

This study investigates harmonic generation in YBCO microwave resonators, revealing nonlinear behaviors and higher harmonic responses that challenge simple theoretical predictions, with measurements supporting a more complex nonlinear impedance model.

Contribution

It demonstrates that higher order nonlinear impedance terms explain the observed harmonic power dependence without additional assumptions.

Findings

Third harmonic power shows a nonlinear dependence with slopes between 1.5 and 3.

Fifth harmonic power measurements confirm the nonlinear behavior.

Small second harmonic power observed with no anomalous dependence.

Abstract

Measurement of harmonic power on a suspended stripline microwave resonator patterned out of thin film YBa_2Cu_3O_7 (YBCO) has been carried out as a function of temperature and microwave power. The third harmonic power P_3 shows a subtle nonlinear dependence on the fundamental power P_1 on a log-log scale. Fit to a straight line yields slopes of P_3 vs. P_1 between 1.5 to 3, contrary to elementary calculations that predict a slope of exactly 3. It is shown that third harmonic power generated from higher order terms in the nonlinear impedance could account for the discrepancy quantitatively without resorting to any additional ad-hoc assumptions. Results of measurement of fifth harmonic power is presented as a confirmation. A small second harmonic power is also observed that does not show anomalous power dependence within the experimental accuracy.