Friday, October 12, 2018

Abstract-Optical tuning of dielectric properties of La0.7Sr0.3MnO3/SrTiO3 superlattices in the terahertz range

Honglei Cai, Haoliang Huang, Qiuping Huang, Xiang Hu, Jie Zhang, Xiaofang Zhai,  Yalin Lu

Fig. 2 (a) Schematic diagram of the home-made THz-TDS system. The green arrow indicates the excitation under 532 nm continuous waves. (b) Schematic diagram of the home-made OPTP system. Here, λ/4 and W.P. refer to a quarter-wave plate and a Wollaston prism, respectively.

Two (La0.7Sr0.3MnO3)n/(SrTiO3)m superlattices with different superlattice period but the same total thickness were deposited on LaAlO3 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 La0.7Sr0.3MnO3 thin film in the OPTP measurements, indicating that the electrons excited in the La0.7Sr0.3MnO3 layers may be trapped by the defects located in the interfaces of La0.7Sr0.3MnO3 and SrTiO3 or the SrTiO3 layers. With the optical field-induced tunability of dielectric properties, (La0.7Sr0.3MnO3)n/(SrTiO3)m superlattices show great potential in the actively tunable devices in the THz range.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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