Third harmonic generation from collective modes in disordered superconductors
Third harmonic generation from collective modes in disordered superconductors
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DOI：
10.1103/physrevb.103.014512
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发表时间：
2021-01-20
影响因子：
3.7
通讯作者：
Benfatto, L.
中科院分区：
文献类型：
--
作者：
Seibold, G.;Udina, M.;Benfatto, L.
最近在传统和非传统超导体中进行的强THz场实验清楚地证明了在超导温度Tc以下显着的三次谐波产生。它的解释挑战了大量的理论工作，旨在建立准粒子激发和集体模式在触发这种共振响应的相对效率。在这里，我们通过实施时间相关的Bogoljubov-de Gennes方法来计算非线性电流，其双重目标是非微扰地考虑局部无序的影响，并包括所有集体模式的贡献，即，超导振幅（希格斯）和相位波动，以及电荷波动。我们表明，在协议与以前的工作，已经在小无序的准粒子响应占主导地位的顺磁效应。我们进一步证明，顺磁过程也调解所有集体模式的响应，与电荷/相位波动的实质性贡献。这些过程，这一直被忽视到目前为止，原来主导的三阶电流在强无序。此外，我们表明，无序强烈影响的非线性响应的偏振依赖性，清洁和无序的情况下有显着的差异。我们的研究结果是特别相关的铜酸盐，其能带结构是在我们的晶格模型再现的第一近似最近的实验。
Recent experiments with strong THz fields in both conventional and unconventional superconductors have clearly evidenced a marked third-harmonic generation below the superconducting temperature T-c. Its interpretation challenged substantial theoretical work aimed at establishing the relative efficiency of quasiparticle excitations and collective modes in triggering such a resonant response. Here we compute the nonlinear current by implementing a time-dependent Bogoljubov-de Gennes approach, with the twofold aim to account nonperturbatively for the effect of local disorder, and to include the contribution of all collective modes, i.e., superconducting amplitude (Higgs) and phase fluctuations, and charge fluctuations. We show that, in agreement with previous work, already at small disorder the quasiparticle response is dominated by paramagnetic effects. We further demonstrate that paramagnetic processes mediate also the response of all collective modes, with a substantial contribution of charge/phase fluctuations. These processes, which have been overlooked so far, turn out to dominate the third-order current at strong disorder. In addition, we show that disorder strongly influences the polarization dependence of the nonlinear response, with a marked difference between the clean and the disordered case. Our results are particularly relevant for recent experiments in cuprates, whose band structure is in a first approximation reproduced by our lattice model.