- The Laboratory has conducted experimental research of magneto-optical interactions in the «pulse formation» configuration in rare-earth garnets and orthoferrites. We used experimental schemes with and without an amplifier. Using terahertz atomic emission spectroscopy we have studied the role of Dy3+ ions in in the DyFeO3 antiferromagnetic in the presence of a femtosecond optical control by magnetism. We have analyzed the emission spectrum, its polarization and temperature laws. It is stated that resonance optical pumping with Dy3+ launches dynamics of magnetization intensity of these ions. We have found that due to d-f exchange interaction between spins of Fe3+ and Dy3+, optically induced magnetization intensity of Dy3+ can induce Fe3+ spin waves by pulses.
- Our researchers have demonstrated existence of a new boundary between terahertz field and spin in antiferromagnetics, which is an electric dipole transition related to magnetic degree of freedom of electrons. As a result of this, we have implemented the first nonlinear excitation of spin waves using terahertz pulses. Spectral sensitivity and high efficiency of this excitation in comparison with Zeeman excitation opens an unprecedented path to future increase of amplitude of spin waves produced by terahertz pulses. To achieve increase of amplitude it is necessary to form impulse and control coherence. For the whole diversity of rare-earth metals we have predicted the threshold value for magnetic switching induced by a terahertz field that can be reduced by an order of magnitude.
- We have tested a new concept of controlled magnetic excitation by electric field that uses hidden states of matter including spin degrees of freedom. We also have an opportunity to research the role of other low energy elementary excitation, such as excitons or phonons that can change orbital wave functions of nearby atoms and lead to a mechanism of formation of magnons. New principles of disturbance of symmetry as a preparation of low energy non-thermal state open new applications for future spintronics devices.
- Using magneto-optical spectroscopy with high temporal resolution we have conducted experimental research of laser-induced dynamics of magnetization intensity in magnetically soft iron-containing films and in thin films of magnetic spinels. Super-fast dynamic of magnetic spinels has been studied using probing by terahertz radiation. We used wide band radiation in the range between 0.2 THz and 2.2 THz in the Voigt geometry. We have suggested a model of projection of electric field of a THz pulse onto the plane of a sample and studied parameters of rotation of polarization and ellipticity depending on applied electric field for various temperatures. Relying on obtained results we have suggested a justification of feasibility of magnetization intensity switching in such media.
- We have developed a methodology and conducted experimental research of super-fast dynamic of electrons and spins in multiferroic hexagonal manganites using the method of optical «pump-probe» and conducted comparison of results of experiments with already available data and research possibility of usage of samples for switching polarization by super-short optical pulses.
- The Laboratory has conducted experimental research of super-fast processes excited by femtosecond laser pulse in the Sn2P2S6 segnetoelectric-emiconductor.
- We have demonstrated possibility of soft-mode excitation of in a crystal and change of its parameters induced by laser radiation. We have demonstrated possibility of excitation of two phonon modes in Sn2P2S6 monocrystals: modes with frequency of 20.5 GHz corresponding to acoustic phonon and a mode with frequency of 0.89 THz whose parameters corresponds parameter of soft-mode in this segnetoelectric. Similarly to the soft mode, observed high-frequency oscillation are characterized by fast attenuation.
- We have demonstrated that after excitation of high-frequency oscillations their frequency significantly changes «softening» over time periods of the order of magnitude of 10 ps. Such behavior can attest to a phase transition in the segnetoelectric that is induced by a femtosecond laser pulse and develops in picosecond time periods.
- Our Laboratory has conducted research of the structure and basic physical qualities of new materials who potentially possess super-fast response to femtosecond laser pulses, as well as researched dynamic response of these media induced by laser radiation. We have researched impact of concentration of Ba cations on polarization qualities of the segnetoelectric layer included into a bilayer structures.
- The Laboratory has create bilayer nanostructures consisting of a Ba(х)Sr(1-x)TiO3(BST) segnetoelectric layer and a ferromagnetic layer La0.7Sr0.3MnO3 (LSMO) with different concentrations of Ва. Epitaxial BST/LSMO heterostructures have been produced using the metalorganic aerosol deposition (MAD) onto monocrystalline SrTiO3 base (001). Structural parameters of BST/LSMO have been determined using X-ray diffraction. segnetoelectric polarization measured using the method of second harmonic generation has shown strong dependence on concentration of Ba.
- We have conducted experimental research of electro-optical interaction in the «pump-probe» configuration on a femtosecond system without amplifiers in films and structures based on SrTiO3 and BiFeO3. In strontium titanate films we have detected a correlation between intensity of the second harmonic and electric field of a terahertz pulse. Our researchers have conducted experimental research of super-fast laser-induced dynamic in type-II multiferroics.
- Our researchers have formulated physical principles of functioning of super-fast (THz) devices based in researched materials and effects. The magneto-optical Faraday effect plays an important role in understanding of electromagnetic nature of light. We have proposed a conceptually new approach to super-fast adjustable modulation using opposite-propagating laser pulses. Through the examples of of paramagnetic terbium gallate garnet (Tb3Ga5O12) we have shown possibility of adjustment of magneto-optical modulation with frequency of up to 1.1. THz under an external magnetic field.
- Our researchers have conducted research of possibility of excitation of high amplitude dynamic of lattice by optical pulses and its impact on dielectric polarization in segnetoelectrics. We have studied spectral correlations of generation of the second optical harmonic as well as luminescence under two-photon excitation for a crystal of the Sn2P2S6 segnetoelectrics-semiconductor. It has been determined that if wave length of exciting radiation from 750 to 950 nm intensity of second harmonic generation related to polarization of the segnetoelectric grows rapidly, increasing approximately by two orders of magnitude while intensity of the peak of luminescence reaches maximum when length of pumping wave is around 880 nm. Characteristic time of recombination of electrons from the conductivity zone to the valence zone is 620 ps. It has been shown that impact of light does not lead to super-fast heating or change of the Curie temperature while the most possible reason of observed changes of photo-induced dynamic of intensity of second harmonic generation is photo-induced charge carriers shielding the part of electric polarization that is probed by the second optical harmonic.
- We have conducted experimental research of feasibility of excitation of soft modes and repolarization in segnetoelectrics using THz pulses (in single and cascade modes). We have experimentally studied of super-fast switching of dielectric polarization by a strong electric field of a single-period THz pulse in a thin film of barium strontium titanate. Review of sources of second harmonic generation in the segnetoelectric leads to a conclusion that temporal correlation between intensity of second harmonic generation means change of polarization in the region of action of the THz pulse, but does not mean transfer of ions between minimums of the potential wells, i. e. true segnetoelectric switching. Nevertheless, the observed effect can be used for remote controlled optoelectronic devices, in particular in super-fast THz modulators.
- Our researchers have investigated exciton/trion energy structure of 2D layers of transition metal dichalcogenides (TMD) at low temperatures using the method of optical spectroscopy (including second harmonic generation). We have researched films of TMD (MoS2, MoSe2, WS2, WSe2) as well as solid solutions based on them. Additionally in this domain over the reported stage of the project we have conducted research of distribution of of electrostatic field and potential as well as local piezoelectric properties in self-assembled diphenylamine microtubes (FF PMT) within composite graphene oxide / metallic nanoparticles / FF PMT structures. Results of research will allow to propose models and determine mechanisms of donor-acceptor interactions in such composite systems. These results can be also used for research in the field of development of energy efficient devices.
- We have conducted research of dynamics of the magnetic parameter of order in ferromagnetics and segnetoelectric. It has been shown that in NdFeCo even faster dynamic of magnetization intensity than the one that can be detected using the magneto-optical Kerr effect. This dynamic remains unnoticeable without usage of methods sensitive to aggregate magnetization intensity (such as, for example, the THz emission method), or methods sensitive to absolutely every components of magnetization intensity
- The Laboratory has experimentally researched spatial and temperature processes occurring at various scales during spiral-dependent fully optical switching in ferromagnetic multi-layer Co/Pt structures. It has been shown that magnetic switching has the nature of an impulse. It has also been shown that multi-pulse switching in thin ferromagnetic films occurs by random formation of seeds of directed domains followed by spiral-dependent determined growth of movement of domain walls. We have determined the mode and frequency of repetition of pulses (100 Hz) under which accumulation of heat affects growth if revers magnetic domains.
- Our researchers have completed comparative analysis of direct and indirect (through phonons) excitations. We have demonstrated selective super-fast excitation of magnetic dipole and electric dipole active modes of rare-earth ions in crystals of ErFeO3 using intra-impulse Raman light scattering. It has been shown that in case when optical dielectric function can be attributed not only to electric dipole transitions (mainly in sublattices of iron) but also to magnetic dipole transfers (mainly in rare-earth sublattices), magnetic dipole-active THz modes respond with electric dipole virtual optical transfer while electric dipole-active THz modes mainly react to magnetic dipole virtual optical transitions. Obtained experimental results require development of theoretical models beyond standard electro-dipole approximation.
- The Laboratory has conducted experimental research aimed at investigation of dynamics of electrons, lattices and spins in a series of model ferroics and dynamics of parameters of order induced by single-period terahertz pulses with electric field intensity of up to 80 MV/cm and magnetic field intensity of up to 27 T related to them.
- We have conducted experimental research of excitation of soft mode and search of experimental conditions for switching of polarization in perovskites by a sub-period THz pulses (in single and cascade modes) with registration of signals at the frequency of second optical harmonic. In solid solution of lead zirconate titanate with Pb0.53Zr0.47TiO3 stoichiometric composition we could observe strong polar modes in the range between 50 and 80 cm-1 at room temperature that can be resonantly excited by single-period THz pulses. It has been shown that behavior of nonlinear optical response is characteristic for the case when induced changes by a THz pulse are comparable or less that own value of the signal of the second optical harmonic in the non-excited state.
Implemented results of research: Results of the projects can be potentially used for development of highly efficient THz antennas for various practical applications (medicine, security, etc).
Education and career development:
- We have compiled and read the following lecture courses at the Moscow Technological University: «Super-fast processes in functional materials» (2014–2015), «Super-fast control of state of ordered media: from basics to devices» (2016) and «Super-fast processes in functional materials» (2017) for students and postgraduates.
- Courses «Methods of diagnostics and analysis of micro- and nanosystems», «Physics of dielectrics», «Nanotechnologies in electronics», «Photonics», «Quantum mechanics», «Femtosecond laser systems, «Optical methods of diagnostics of nanostructures» and others are read for masters students studying in the specialization 28.04.01 «Nanotechnologies and microsystem devices», and bachelors studying in the specialization 11.03.04 «Electronics and nanoelectronics».
- We have developed the education course «Optical methods of diagnostics of nanostructures», it has been tested in English on the grounds of the University of Regensburg (Germany) within the «Invited lecturers» national program.
Organizational and structural changes:
The Laboratory has purchased measuring and research equipment produced by leading manufacturers – Spectra Physics, Newport, Stanford Research, Hamamatsu and others. The core of laser equipment of the Laboratory is comprised by laser femtosecond equipment manufactured by «Avesta-Proekt» LLC (Russia). The company provides technical maintenance and emergency repair of equipment. All the experimental research is conducted in automatic mode using software developed by performers of the project. To perform specific tasks within the project the hosting organization provided access to equipment and methodologies of the «Electronics» Collective Usage Center of the Moscow Technological University free of charge.
Other results:
- The Laboratory has conducted meetings of the «Dynamics of ferroics» seminars with participation of representatives of universities and research institutes of the Russian Academy of Sciences on the grounds of the Moscow Technological University, the Institute of Physical Problems of the Russian Academy of Sciences, the Institute for High Temperatures of the Russian Academy of Sciences, and the Faculty of Physics of the Moscow State University.
- At the International Conference «Fundamental problems of Radioelectronic Engineering» (INTERMATIC-2014, 2015, 2016, 2017) we have organized and rum subsections with presentations of keynotes showcasing scientific work of the Laboratory.
Collaborations:
- Institute for Molecules and Materials of the Institute for Molecules and Materials (the Netherlands), Joint Institute for High Temperatures of the Russian Academy of Sciences (Russia): joint research
- Institute of Electronics, Microelectronics and Nanotechnology (France), Institute of Ultra High Frequency Semiconductor Electronics of the Russian Academy of Sciences (Russia): joint projects funded by the Russian Foundation for Basic Research
