Golež Denis, Sun Zhiyuan, Murakami Yuta, Georges Antoine, Millis Andrew J
Center for Computational Quantum Physics, Flatiron Institute, 162 Fifth Avenue, New York, New York 10010, USA.
Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.
Phys Rev Lett. 2020 Dec 18;125(25):257601. doi: 10.1103/PhysRevLett.125.257601.
The nonlinear optical response of an excitonic insulator coupled to lattice degrees of freedom is shown to depend in strong and characteristic ways on whether the insulating behavior originates primarily from electron-electron or electron-lattice interactions. Linear response optical signatures of the massive phase mode and the amplitude (Higgs) mode are identified. Upon nonlinear excitation resonant to the phase mode, a new in-gap mode at twice the phase mode frequency is induced, leading to a huge second harmonic response. Excitation of in-gap phonon modes leads to different and much smaller effects. A Landau-Ginzburg theory analysis explains these different behaviors and reveals that a parametric resonance of the strongly excited phase mode is the origin of the photoinduced mode in the electron-dominant case. The difference in the nonlinear optical response serves as a measure of the dominant mechanism of the ordered phase.
研究表明，与晶格自由度耦合的激子绝缘体的非线性光学响应，强烈且具有特征性地取决于绝缘行为主要源于电子-电子相互作用还是电子-晶格相互作用。确定了大质量相模式和振幅（希格斯）模式的线性响应光学特征。当非线性激发与相模式共振时，会诱导出频率为相模式两倍的新能隙模式，从而导致巨大的二次谐波响应。能隙声子模式的激发会产生不同且小得多的效应。朗道-金兹堡理论分析解释了这些不同行为，并揭示在电子主导情况下，强激发相模式的参量共振是光诱导模式的起源。非线性光学响应的差异可作为有序相主导机制的一种度量。
