We present a new approach for nonlinear induction detection of electron spin resonance (ESR) signals.  We utilize a superconducting stripline microwave (MW) resonator integrated with a microbridge. A strong nonlinear response of the resonator is thermally activated in the microbridge, when passing a threshold in the power of the injected MW signal. When operating the resonator near this threshold and under a static magnetic field which brings spins in the sample into ESR, a strong enhancement in the responsivity of the ESR signal is seen. Preliminary experimental results, along with a theoretical model of this phenomenon and its sensitivity analysis are presented.  It is shown that under appropriate conditions nonlinear induction detection of ESR can greatly improve upon the current capabilities of conventional linear induction detection of ESR.

[1] Appl. Phys. Lett. 101, 22602 (2012) doi:10.1063/1.4734500