Dynamic pair-breaking current, critical superfluid velocity, and nonlinear electromagnetic response of nonequilibrium superconductors
Dynamic pair-breaking current, critical superfluid velocity, and nonlinear electromagnetic response of nonequilibrium superconductors
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DOI：
10.1103/physrevb.102.104507
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发表时间：
2020-08
影响因子：
3.7
通讯作者：
Ahmad Sheikhzada;A. Gurevich
中科院分区：
文献类型：
--
作者：
Ahmad Sheikhzada;A. Gurevich
我们报告了在非平衡超导体中动态破对电流密度$J_d$和临界超流体速度$v_d$的数值计算，该超导体携带均匀的、振幅较大的交流电流密度$J(t)=J_a\sin\Omega t$，其$\Omega$远低于间隙频率$\Omega\ll \Delta_0/\hbar$。考虑到序参量的GL弛豫时间$\tau_{GL}$和准粒子的非弹性电子-声子弛豫时间$\tau_E$，分别从脏s波超导体的完全时变非平衡方程和间隙超导体的时变金兹堡-朗道（TDGL）方程计算了临界温度$T_c$附近的依赖关系$J_d(\Omega,T)$和$v_d(\Omega,T)$。我们表明，这两种方法给出了相似的$J_d(\Omega)$和$v_d(\Omega)$的频率依赖关系，从它们的静态破对GL值$J_c$和$v_c$ （$\Omega\tau_E\ll 1$）逐渐增加到$\sqrt{2}J_c$和$\sqrt{2}v_c$ （$\Omega\tau_E\gg 1$）。本文计算了细长超导灯丝或具有大GL参数的ii型超导体在施加交流磁场$H=H_a\sin\Omega t$引起的固定交流电流和固定交流超流体速度两种不同状态下$J_d$, $v_d$和迈斯纳状态变得不稳定的动态过热场。我们还计算了非平衡超导态的非线性电磁响应，特别是动态动力学电感和耗散准粒子电导率，考虑了超导凝聚体的振荡动力学和强交流电流驱动下准粒子的动力学。结果表明，交流电流密度产生电场的多次谐波，高次谐波的振幅随着$\tau_E$的增加而减小。
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 $J(t)=J_a\sin\Omega t$ with $\Omega$ well below the gap frequency $\Omega\ll \Delta_0/\hbar$. The dependencies $J_d(\Omega,T)$ and $v_d(\Omega,T)$ 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 $\tau_{GL}$ and the inelastic electron-phonon relaxation time of quasiparticles $\tau_E$. We show that both approaches give similar frequency dependencies of $J_d(\Omega)$ and $v_d(\Omega)$ which gradually increase from their static pairbreaking GL values $J_c$ and $v_c$ at $\Omega\tau_E\ll 1$ to $\sqrt{2}J_c$ and $\sqrt{2}v_c$ at $\Omega\tau_E\gg 1$. 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 $H=H_a\sin\Omega t$ 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 $\tau_E$ increases.