Origins of Nonlinearity in Superconductive Passive Circuits

The distinct origins of even and odd order nonlinear behavior in type II cuprate superconductors have yet to be fully elucidated. Microwave intermodulation distortion (IMD) was examined in a YBCO superconducting thin-film hairpin resonator at 840 MHz. Measurements of the temperature dependence of IMD near T$_{\mathrm{C\thinspace }}$support the view that the nonlinear Meissner effect is responsible for the occurrence of both 2$^{\mathrm{nd}}$ and 3$^{\mathrm{rd}}$ order IMD tones near T$_{\mathrm{C\thinspace }}$as well as their suppression in an applied magnetic field. However, at lower reduced temperatures (T/ T$_{\mathrm{C}}$ less than 0.95), where the influence of the nonlinear Meissner effect is less pronounced, 3$^{\mathrm{rd}}$ order IMD is unaffected by a static magnetic field, while 2$^{\mathrm{nd}}$ order IMD decays exponentially after a static magnetic field is removed with a temperature dependent time constant. It is apparent that the magnetically induced remnant vortex state contributes to the 2$^{\mathrm{nd}}$ order nonlinearity, but not to the 3$^{\mathrm{rd}}$ order nonlinearity, and that this effect is diminished close to T$_{\mathrm{C\thinspace }}$due to degradation of the remnant vortex state.