Annihilation of topological solitons in magnetism with spin-wave burst finale: Role of nonequilibrium electrons causing nonlocal damping and spin pumping over ultrabroadband frequency range
Annihilation of topological solitons in magnetism with spin-wave burst finale: Role of nonequilibrium electrons causing nonlocal damping and spin pumping over ultrabroadband frequency range
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DOI：
10.1103/physrevb.104.l020407
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发表时间：
2019-08
影响因子：
3.7
通讯作者：
M. Petrović;U. Bajpai;P. Plecháč;B. Nikolić
中科院分区：
文献类型：
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作者：
M. Petrović;U. Bajpai;P. Plecháč;B. Nikolić
我们不仅再现了最近实验中观察到的短波长自旋波爆发[S。Woo等人，13，448（2017）]，但是，此外，我们预测，在没有任何偏置电压的情况下，这种设置还产生了电子自旋电流的极不寻常的泵浦。在湮灭的瞬间之前，它们的功率谱是超宽带的，因此它们可以通过逆自旋霍尔效应被转换成快速变化的时间电荷电流，作为带宽为$\simeq 27$ THz的THz辐射源，其中最低频率由所施加的磁场控制。自旋泵源于由包括畴的局域磁矩（Lmf）的经典动力学引入到电子的量子哈密顿量中的与时间相关的场。泵浦电流携带自旋极化的电子，反过来，施加反作用在非局部阻尼的形式，这是传统的本地吉尔伯特阻尼的两倍以上。的非本地阻尼可以大大修改发射SW的频谱相比，广泛使用的微磁模拟传导电子完全不存在。由于我们使用完全微观（即，Hamilton）框架下，自洽地将含时电子非平衡绿色函数与Landau-Lifshitz-吉尔伯特方程相结合，我们还证明了以前推导的唯象公式忽略了超宽带自旋抽运，同时低估了非平衡电子引起的非局域阻尼的大小.
We not only reproduce burst of short-wavelength spin waves (SWs) observed in recent experiment [S. Woo et al., Nat. Phys. 13, 448 (2017)] on magnetic-field-driven annihilation of two magnetic domain walls (DWs) but, furthermore, we predict that this setup additionally generates highly unusual} pumping of electronic spin currents in the absence of any bias voltage. Prior to the instant of annihilation, their power spectrum is ultrabroadband, so they can be converted into rapidly changing in time charge currents, via the inverse spin Hall effect, as a source of THz radiation of bandwidth $\simeq 27$ THz where the lowest frequency is controlled by the applied magnetic field. The spin pumping stems from time-dependent fields introduced into the quantum Hamiltonian of electrons by the classical dynamics of localized magnetic moments (LMMs) comprising the domains. The pumped currents carry spin-polarized electrons which, in turn, exert backaction on LMMs in the form of nonlocal damping which is more than twice as large as conventional local Gilbert damping. The nonlocal damping can substantially modify the spectrum of emitted SWs when compared to widely-used micromagnetic simulations where conduction electrons are completely absent. Since we use fully microscopic (i.e., Hamiltonian-based) framework, self-consistently combining time-dependent electronic nonequilibrium Green functions with the Landau-Lifshitz-Gilbert equation, we also demonstrate that previously derived phenomenological formulas miss ultrabroadband spin pumping while underestimating the magnitude of nonlocal damping due to nonequilibrium electrons.