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首页> 外文期刊>Physical review >Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulator Bi_2Se_3
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Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulator Bi_2Se_3

机译：拓扑绝缘体Bi_2Se_3薄膜中光学二次谐波产生的共振型厚度依赖性

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摘要

Optical second-harmonic generation (SHG) has been measured in a reflection from the nanometer-thick films (6 to 40 nm) of the topological insulator Bi_2Se_3 using 1.51 eV (820 nm) Ti:Sapphire laser photons and revealed a strong dependence of the integral SHG intensity on the film thickness. The integral SHG intensity was determined by area integration of the SHG rotational anisotropy patterns measured for different input-output light polarization geometries. A ～100-fold enhancement of the integral SHG intensity with decreasing film thickness has been suggested to result from the dc-electric-field-induced SHG (EFISHG) effects. Two sources of dynamically created dc electric field were proposed: (ⅰ) the capacitor-type dc electric field that gradually increases with decreasing film thickness from 40 to 6 nm due to a dynamical imbalance of photoexcited long-lived carriers between the opposite-surface Dirac surface states and (ⅱ) a dc electric field associated with a nonlinearly excited Dirac plasmon, which is responsible for the resonant enhancement of the integral SHG intensity for the 10 nm thick film with a Lorentz-shaped resonance of ～1.6 nm full width at half maximum. In addition to the general SHG enhancement trends with decreasing film thickness, a relative decrease of the out-of-plane contribution with respect to the in-plane contribution was observed. Using a theoretical treatment of the measured SHG rotational anisotropy patterns, this effect has been suggested to result from the joint contributions of the linear and quadratic dc electric field effects to the EFISHG response.
机译：在使用1.51 eV（820 nm）的Ti：蓝宝石激光光子从拓扑绝缘体Bi_2Se_3的纳米厚膜（6至40 nm）的反射中测量了光学二次谐波（SHG）的产生，并显示出强烈的依赖性​​。 SHG强度对薄膜厚度的影响。通过对不同输入输出光偏振几何形状测量的SHG旋转各向异性图案的面积积分，可以确定SHG积分强度。直流电场诱导的SHG（EFISHG）效应导致SHG积分强度随薄膜厚度的减小而增加了约100倍。提出了两种动态产生的直流电场的来源：（ⅰ）由于对面狄拉克晶体之间光激发的长寿命载流子的动态失衡，电容器型直流电场随着膜厚从40 nm减小到6 nm而逐渐增加表面状态和（ⅱ）与非线性激发的Dirac等离子体激元相关的直流电场，这是共振增强了10 nm厚膜的整体SHG强度的共振，其Lorentz形共振的半峰全宽约为1.6 nm最大。除了随着膜厚度减小一般的SHG增强趋势外，还观察到面外贡献相对于面内贡献的相对减少。使用理论方法对测得的SHG旋转各向异性模式进行处理，已表明此效应是由于线性和二次直流电场效应对EFISHG响应的共同贡献所致。

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