Walter Schottky Institut and Physik Department, Technische Universität München , Am Coulombwall 4, 85748 Garching, Germany.
Institut für Theoretische Physik, Universität Bremen , P.O. Box 330 440, 28334 Bremen, Germany.
Nano Lett. 2017 Jan 11;17(1):392-398. doi: 10.1021/acs.nanolett.6b04344. Epub 2016 Dec 19.
We demonstrate pronounced electric-field-induced second-harmonic generation in naturally inversion symmetric 2H stacked bilayer MoS embedded into microcapacitor devices. By applying strong external electric field perturbations (|F| = ±2.6 MV cm) perpendicular to the basal plane of the crystal, we control the inversion symmetry breaking and, hereby, tune the nonlinear conversion efficiency. Strong tunability of the nonlinear response is observed throughout the energy range (E ∼ 1.25-1.47 eV) probed by measuring the second-harmonic response at E, spectrally detuned from both the A- and B-exciton resonances. A 60-fold enhancement of the second-order nonlinear signal is obtained for emission at E = 2.49 eV, energetically detuned by ΔE = E - E = -0.26 eV from the C-resonance (E = 2.75 eV). The pronounced spectral dependence of the electric-field-induced second-harmonic generation signal reflects the bandstructure and wave function admixture and exhibits particularly strong tunability below the C-resonance, in good agreement with density functional theory calculations. Moreover, we show that the field-induced second-harmonic generation relies on the interlayer coupling in the bilayer. Our findings strongly suggest that the strong tunability of the electric-field-induced second-harmonic generation signal in bilayer transition metal dichalcogenides may find applications in miniaturized electrically switchable nonlinear devices.
我们在自然反演对称的 2H 堆叠双层 MoS 嵌入微电容器器件中展示了明显的电场诱导二次谐波产生。通过施加垂直于晶体基面的强外部电场扰动（|F|=±2.6 MV cm），我们控制了反演对称性的破坏，并由此调整了非线性转换效率。在通过测量与 A-和 B-激子共振光谱失谐的 E 处的二次谐波响应来探测的能量范围内（E∼1.25-1.47 eV），观察到非线性响应的强可调性。对于在 E = 2.49 eV 处发射的光，获得了 60 倍的二阶非线性信号增强，其能量从 C-共振（E = 2.75 eV）偏移ΔE = E - E = -0.26 eV。电场诱导二次谐波产生信号的明显光谱依赖性反映了能带结构和波函数混合，并在 C-共振以下表现出特别强的可调性，与密度泛函理论计算吻合良好。此外，我们表明，场诱导二次谐波产生依赖于双层中的层间耦合。我们的发现强烈表明，在双层过渡金属二卤化物中，电场诱导二次谐波产生信号的强可调性可能在小型化电可切换非线性器件中得到应用。
