Cai Honglei, Huang Haoliang, Huang Qiuping, Hu Xiang, Zhang Jie, Zhai Xiaofang, Lu Yalin
Opt Express. 2018 Mar 19;26(6):7842-7851. doi: 10.1364/OE.26.007842.
Two (LaSrMnO)n/(SrTiO)m superlattices with different superlattice period but the same total thickness were deposited on LaAlO substrates by pulsed laser deposition. Dielectric properties of these samples were investigated by means of terahertz time-domain spectroscopy (THz-TDS) under external continuous wave green laser excitation and optical-pump terahertz-probe spectroscopy (OPTP) at room temperature. Experimental results show that the real part of the permittivity for both superlattices increases significantly with increasing green laser pump power, which indicates the decrease of the plasma frequency, along with the increase of the electron scattering rate, soft mode eigenfrequency and oscillator strength in the Drude-Lorentz model. Furthermore, it's observed that the insulating superlattice exhibits a more significant dielectric tunability than the metallic superlattice. Besides, the carrier lifetime of superlattices is much shorter than the LaSrMnO thin film in the OPTP measurements, indicating that the electrons excited in the LaSrMnO layers may be trapped by the defects located in the interfaces of LaSrMnO and SrTiO or the SrTiO layers. With the optical field-induced tunability of dielectric properties, (LaSrMnO)n/(SrTiO)m superlattices show great potential in the actively tunable devices in the THz range.
通过脉冲激光沉积法，在镧铝氧（LaAlO）衬底上制备了两种具有不同超晶格周期但总厚度相同的（LaSrMnO）n/（SrTiO）m超晶格。在室温下，利用太赫兹时域光谱（THz - TDS）在外加连续波绿色激光激发下以及光泵浦太赫兹探测光谱（OPTP）对这些样品的介电性质进行了研究。实验结果表明，随着绿色激光泵浦功率的增加，两种超晶格的介电常数实部均显著增加，这表明在德鲁德 - 洛伦兹模型中，等离子体频率降低，同时电子散射率、软模本征频率和振子强度增加。此外，观察到绝缘超晶格比金属超晶格表现出更显著的介电可调性。此外，在OPTP测量中，超晶格的载流子寿命比LaSrMnO薄膜短得多，这表明在LaSrMnO层中激发的电子可能被位于LaSrMnO与SrTiO界面或SrTiO层中的缺陷捕获。凭借光场诱导的介电性质可调性，（LaSrMnO）n/（SrTiO）m超晶格在太赫兹波段的有源可调器件中显示出巨大潜力。
