The lineshape in an auto-oscillator with a large nonlinear frequency shift in the presence of thermal noise is calculated. Near the generation threshold, this lineshape becomes strongly non-Lorentzian, broadened, and asymmetric. A Lorentzian lineshape is recovered far below and far above threshold, which suggests that lineshape distortions provide a signature of the generation threshold. The theory developed adequately describes the observed behavior of a strongly nonlinear spin-torque nano-oscillator.
@article{arxiv.0710.0495,
title = {Lineshape distortion in a nonlinear auto-oscillator near generation threshold: Application to spin-torque nano-oscillators},
author = {Joo-Von Kim and Q. Mistral and C. Chappert and V. S. Tiberkevich and A. N. Slavin},
journal= {arXiv preprint arXiv:0710.0495},
year = {2009}
}