SEMINAR

　　Synthetic Crystal Research Center, Shanghai Institute of Ceramics

　　Key Laboratory of Transparent Opto-functional Inorganic Materials, CAS

　　人工晶体研究中心、中国科学院透明光功能无机材料重点实验室

　　

　　莫斯科科技大学及俄罗斯科学院约飞技术物理所

　　来访学术交流报告

　　

　　报告时间：2018年3月30日（周五）下午14:30~17:00

　　报告地点：长宁园区4号楼3楼会议室

　　联系人：武安华（021-52414242）

　　

　　报告一

　　Ultrafast optical and THz control over ferroic materials

　　

　　Prof. Dr. Elena D. Mishina, Head of the laboratory

　　Femtosecond optics for nanotechnology, Moscow Technological University

　　

　　The ability to switch dielectric polarization in ferroelectics is responsible for their unique functionalities allowing them to serve as the key component in memories, actuators, other electronic and electro-optic devices.. The speed of the switching defines the maximum operational frequency of such devices. Fundamentally, polarization reversal cannot be done faster than the period of optical phonon which is about τ0 ≈ 10?13 s. The fastest switching of the dielectric polarization was achieved in 220 ps using electric field pulse generated with the help of a photoswitch triggered by femtosecond laser pulses.

　　Recently sub-cycle THz pulses were proposed to control the order parameter in ferroics. Similarly, it was proposed to control the magnetic order parameter and trigger spin-reorientation using the electric component of a nearly single cycle THz pulse. In ferroelectrics, the possibility of a dynamical switching of the dielectric polarization by a strong THz pulse was also discussed previously. Since the action of the electric component of light with charges is the strongest perturbation in light-matter interaction, switching order parameter in ferroelectrics by strong THz pulses remains to be a promising research direction.

　　Since the phenomenon of optical second harmonic generation (SHG) is sensitive to both spatial inversion (SI) and time reversal (TI) symmetry breaking, it provides a powerful experimental technique for investigating of (multi)ferroic materials (see for review). The SHG is able to provide information on surface structural phase transition in SrTiO3. Phonon relaxation excited by optical pulse was studied by the SHG in. Very recently SHG was used as a probe of transient processes in the lattice under intense THz excitationand a possibility of an ultrafast reversal of the dielectric polarization under strong THz pulse was suggested

　　

　　报告二

　　Ultrafast control of magnetic anisotropyby laser-generated heat and strain in low-symmetry films

　　

　　Prof. Dr. Alexandra Kalashnikova, Vice Director of the laboratory

　　Ferroics Physics Laboratory, Ioffe Institute of RAS, St. Petersburg, Russia

　　

　　Femtomagnetism is the emerging field in condensed matter physics, aiming at developing novel approaches for controlling the magnetic state on pico- and subpicosecond time scales by means of ultrashort optical pulses or other unconventional stimuli. In this talk we consider the problem of the ultrafast laser-induced changes of magnetic anisotropy of magnetic metallic and dielectric films, which can serve as an effective way to trigger and control ultrafast dynamics of magnetization. In particular, we discuss how the magnetic anisotropy in a thin film of iron garnet can be controlled via picoseconds laser-induced increase of lattice temperature [1]. Further, we consider the complex impact of femtosecond pulses on magnetic anisotropy of magnetostrictive metallic (Fe,Ga) film and demonstrate the important role the optically-generates dynamical strain plays in this process [2,3]. In both experiments the low symmetry of the studied magnetic films enabled detailed study and deeped understanding of the laser-pulse impact on magnetic anisotropy.

　　[1] L. A. Shelukhin, V. V. Pavlov, P. A. Usachev, et al., Phys. Rev. B 97, 014422 (2018).

　　[2] V. N. Kats, T. L. Linnik, A. S. Salasyuk, et al., Phys. Rev. B 93, 214422 (2016).

　　[3] T. L. Linnik, V. N. Kats, J. J?ger, et al., Phys. Scr. 92, 054006 (2017).