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arXiv 2008.12732cond-mat.supr-con
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非平衡超导体的动态对破断电流、临界超流速度和非线性电磁响应

Dynamic pair-breaking current, critical superfluid velocity and nonlinear electromagnetic response of nonequilibrium superconductors

Ahmad Sheikhzada, Alex Gurevich

摘要:

我们报告的数值计算的一个动态的成对破坏电流密度$J_d$和一个临界超流速度$v_d$在一个非平衡超导体携带一个均匀的,大振幅的交流电流密度$J(t)=J_a\sinΩt$与$Ω$远低于间隙频率$Ω\ll Δ_0/\hbar$。在考虑序参量$τ_{GL}$的含时Ginzburg-Landau(TDGL)弛豫时间和准粒子$τ_E$的非弹性电子-声子弛豫时间的情况下,从含时S波超导体非平衡方程和含时能隙超导体TDGL方程计算了临界温度$T_c$附近的依赖关系$J_d(Ω,T)$和$v_d(Ω,T)$.我们发现,这两种方法给出了类似的频率依赖性的$J_d(Ω)$和$v_d(Ω)$逐渐增加,从他们的静态配对破坏GL值$J_c$和$v_c$在$Ωτ_E\ll 1$的$\sqrt{2}J_c$和$\sqrt{2}v_c$在$Ωτ_E\gg 1$。在这里$J_d$,$v_d$和动态过热场迈斯纳状态变得不稳定,在两个不同的制度下的一个固定的交流电流和一个固定的交流超流速度所引起的外加交流磁场$H=H_a\sinΩt$在薄超导细丝或II型超导体与一个大的GL参数计算。我们还计算了一个非平衡超导态的非线性电磁响应,特别是一个动态的动力学电感和耗散的准粒子电导率,考虑到超导凝聚体的振荡动力学和强交流电流驱动的准粒子的动力学。它示出,交流电流密度产生多个谐波的电场,高次谐波的幅度减小$τ_E$增加。

英文摘要:

We report numerical calculations of a dynamic pairbreaking current density $J_d$ and a critical superfluid velocity $v_d$ in a nonequilibrium superconductor carrying a uniform, large-amplitude ac current density $J(t)=J_a\sinΩt$ with $Ω$ well below the gap frequency $Ω\ll Δ_0/\hbar$. The dependencies $J_d(Ω,T)$ and $v_d(Ω,T)$ near the critical temperature $T_c$ were calculated from either the full time-dependent nonequilibrium equations for a dirty s-wave superconductor and the time-dependent Ginzburg-Landau (TDGL) equations for a gapped superconductor, taking into account the GL relaxation time of the order parameter $τ_{GL}$ and the inelastic electron-phonon relaxation time of quasiparticles $τ_E$. We show that both approaches give similar frequency dependencies of $J_d(Ω)$ and $v_d(Ω)$ which gradually increase from their static pairbreaking GL values $J_c$ and $v_c$ at $Ωτ_E\ll 1$ to $\sqrt{2}J_c$ and $\sqrt{2}v_c$ at $Ωτ_E\gg 1$. Here $J_d$, $v_d$ and a dynamic superheating field at which the Meissner state becomes unstable were calculated in two different regimes of a fixed ac current and a fixed ac superfluid velocity induced by the applied ac magnetic field $H=H_a\sinΩt$ in a thin superconducting filament or a type-II superconductor with a large GL parameter. We also calculated a nonlinear electromagnetic response of a nonequilibrium superconducting state, particularly a dynamic kinetic inductance and a dissipative quasiparticle conductivity, taking into account the oscillatory dynamics of superconducting condensate and the kinetics of quasiparticles driven by a strong ac current. It is shown that an ac current density produces multiple harmonics of the electric field, the amplitudes of the higher-order harmonics diminishing as $τ_E$ increases.

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