本文研究了一个两点电子-声子模型的精确非平衡解，其中一个与电子非线性耦合的红外激活声子被激光场驱动。时间分辨的电子光谱显示相干-非相干光谱重量转移，光增强的电子-声子耦合的一个明确的签名。本研究的动机是最近的证据，增强电子-声子耦合泵浦探测太赫兹和角度分辨光电子能谱在双层石墨烯时，驱动近共振与红外活性声子模式[E.~ Pomarico等人，物理学~修订版~ B 95，024304（2017）]，并通过理论研究表明，瞬态电子吸引力来自非线性电子-声子耦合[D.~ M.~ Kennes等人，Nature Physics（2017），10.1038/nphys4024]。我们表明，光增强电子-声子耦合与泵场强度的线性标度出现，与基于准经典声子相干态的平均场去耦的时间非局域自能一致。最后，我们证明，这导致增强的双occupancy根据有效的电子-电子吸引力。我们的研究结果表明，具有强声子非线性的材料提供了一个理想的游乐场，以实现光增强的电子-声子耦合和可能的光诱导超导。
英文摘要：
We investigate an exact nonequilibrium solution of a two-site electron-phonon model, where an infrared-active phonon that is nonlinearly coupled to the electrons is driven by a laser field. The time-resolved electronic spectrum shows coherence-incoherence spectral weight transfer, a clear signature of light-enhanced electron-phonon coupling. The present study is motivated by recent evidence for enhanced electron-phonon coupling in pump-probe TeraHertz and angle-resolved photoemission spectroscopy in bilayer graphene when driven near resonance with an infrared-active phonon mode [E.~Pomarico et al., Phys.~Rev.~B 95, 024304 (2017)], and by a theoretical study suggesting that transient electronic attraction arises from nonlinear electron-phonon coupling [D.~M.~Kennes et al., Nature Physics (2017), 10.1038/nphys4024]. We show that a linear scaling of light-enhanced electron-phonon coupling with the pump field intensity emerges, in accordance with a time-nonlocal self-energy based on a mean-field decoupling using quasi-classical phonon coherent states. Finally we demonstrate that this leads to enhanced double occupancies in accordance with an effective electron-electron attraction. Our results suggest that materials with strong phonon nonlinearities provide an ideal playground to achieve light-enhanced electron-phonon coupling and possibly light-induced superconductivity.
Superconductivity enhanced by abundant low-energy phonons in (Sr$_{1-x}$Ca$_x$)$_3$Rh$_4$Sn$_{13}$
通过电阻率和比热测量研究了结构量子临界性对（Sr $_{1-x}$ Ca $_x$）$_3$ Rh $_4$ Sn $_{13}$强耦合超导电性的影响。我们表明，在低温下的晶格比热相当大地增加对结构量子临界点（SQCP），$x_{\rm c}\approx0.9$。超导能隙随着$x$的增加而增加，与低温晶格比热的增加方式完全相同，这清楚地表明大量的低能声子导致了强耦合超导性。尽管电子-声子相互作用比电子相关性增强得多，但SQCP附近的低温电阻率变化为$\propto T^2$。这一发现表明，结构量子涨落影响的幂律所产生的电子-声子散射。
Magnetism-Enhanced Strong Electron-Phonon Coupling in Infinite-Layer Nickelate
Tulane University（杜兰大学）；VASP Software GmbH（VASP软件有限公司）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Howard University（霍华德大学）；Tata Institute of Fundamental Research（塔塔基础研究所）；LUT University（拉彭兰塔理工大学）；Northeastern University（东北大学）
Nonlinear electron-phonon interactions from first principles
Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin（德克萨斯大学奥斯汀分校奥登计算工程与科学研究所）；Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校物理系）
