Dielectric nonlinearity and stochastic effects in strontium titanate

We report on experiments using compact coplanar waveguide devices, incorporating thin-film superconducting YBa2Cu3O7 electrodes. The substrate is strontium titanate, whose nonlinear dielectric properties are dependent on temperature and applied electric field. Close to zero dc bias, the frequency-doubled microwave power output increases by several orders of magnitude with modest broadband noise input. Experimental results are supported by analytical and numerical calculations based on a nonlinear wave equation.