A theory of dissipative nonlinear conductivity, $\sigma_1(\omega,H)$, ofs-wave superconductors under strong electromagnetic fields at low temperaturesis proposed. Closed-form expressions for $\sigma_1(H)$ and the surfaceresistance $R_s(\omega,H)$ are obtained in the nonequilibrium dirty limit forwhich $\sigma_1(H)$ has a significant minimum as a function of a low-frequency$(\hbar\omega\ll k_BT)$ magnetic field $H$. The calculated microwavesuppression of $R_s(H)$ is in good agreement with recent experiments on alloyedNb resonator cavities. It is shown that superimposed dc and ac fields,$H=H_0+H_a\cos\omega t$, can be used to reduce ac dissipation in thin filmnanostructures by tuning $\sigma_1(H_0)$ with the dc field.
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机译：提出了一种在低温环境下强电磁场下的耗散非线性电导率$ \ sigma_1（\ omega，H）$的短波超导体的理论。 $ \ sigma_1（H）$和表面电阻$ R_s（\ omega，H）$的闭式表达式是在非平衡脏限制下获得的，对于该限制，$ \ sigma_1（H）$具有一个最小值，该最小值是低阻抗的函数。频率$（\ hbar \ omega \ ll k_BT）$磁场$ H $。计算得到的Rs（H）$的微波抑制与合金化Nb谐振腔最近的实验非常吻合。结果表明，叠加的直流场和交流场$ H = H_0 + H_a \ cos \ωtω，可以通过用dc场调谐$ \ sigma_1（H_0）$来减少薄膜纳米结构的交流损耗。
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