Mennel Lukas, Smejkal Valerie, Linhart Lukas, Burgdörfer Joachim, Libisch Florian, Mueller Thomas
Vienna University of Technology, Institute of Photonics, Gußhausstraße 27-29, 1040 Vienna, Austria, EU.
Vienna University of Technology, Institute of Theoretical Physics, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria, EU.
Nano Lett. 2020 Jun 10;20(6):4242-4248. doi: 10.1021/acs.nanolett.0c00694. Epub 2020 May 21.
Band nesting occurs when conduction and valence bands are approximately equispaced over regions in the Brillouin zone. In two-dimensional materials, band nesting results in singularities of the joint density of states and thus in a strongly enhanced optical response at resonant frequencies. We exploit the high sensitivity of such resonances to small changes in the band structure to sensitively probe strain in semiconducting transition metal dichalcogenides (TMDs). We measure and calculate the polarization-resolved optical second harmonic generation (SHG) at the band nesting energies and present the first measurements of the energy-dependent nonlinear photoelastic effect in atomically thin TMDs (MoS, MoSe, WS, and WSe) combined with a theoretical analysis of the underlying processes. Experiment and theory are found to be in good qualitative agreement displaying a strong energy dependence of the SHG, which can be exploited to achieve exceptionally strong modulation of the SHG under strain. We attribute this sensitivity to a redistribution of the joint density of states for the optical response in the band nesting region. We predict that this exceptional strain sensitivity is a general property of all 2D materials with band nesting.
当导带和价带在布里渊区的某些区域近似等间距时，就会发生能带嵌套。在二维材料中，能带嵌套会导致态密度联合函数出现奇点，从而在共振频率处产生强烈增强的光学响应。我们利用这种共振对能带结构微小变化的高灵敏度，来灵敏地探测半导体过渡金属二硫属化物（TMDs）中的应变。我们测量并计算了在能带嵌套能量处的偏振分辨光学二次谐波产生（SHG），并首次给出了原子级薄的TMDs（MoS、MoSe、WS和WSe）中能量相关的非线性光弹效应的测量结果，并结合了对相关基本过程的理论分析。实验和理论在定性上吻合良好，显示出SHG具有强烈的能量依赖性，可利用这种特性在应变下实现对SHG的异常强烈调制。我们将这种灵敏度归因于能带嵌套区域中光学响应的态密度联合函数的重新分布。我们预测，这种特殊的应变灵敏度是所有具有能带嵌套的二维材料的普遍特性。
