Optical Spectroscopy

Fourier-transform spectroscopy and Ellipsometry Lab

Wide-range optical spectroscopy (190 nm – 1 mm) of superconductors and quantum materials using infrared Fourier-transform spectroscopy (including microscopy) and spectral ellipsometry at temperatures of 4-300K.

The main material to be studied are single crystals (including layered crystals and those with rough surface), films, and quantum structures.

Optical spectroscopy is an important technique for studying electrodynamics in condensed matter physics. The aim of the study is to obtain spectra of optical functions (complex permittivity, complex refractive index, optical conductivity), the interpretation of which in turn provides information about the mechanisms that form them.

The characteristic energies of a significant part of the phenomena in solids correspond to the spectral range from visible radiation to the far-infrared (IR) range, which is manifested in the spectra of optical functions. Thus, wide-range spectroscopy becomes a source of information about the structure of energy bands, the dynamics of charge carriers, impurity levels, localized defects, phonon vibrations, magnetic excitations, etc.

Thus, to obtain the most accurate and complete information on the material, as well as to separate the various contributions that form the spectrum, it is necessary to obtain spectra of optical functions in the entire optical range accessible for measurement.

For measurements in the infrared range of 10-10 000 cm^-1 (wavelength 1 cm – 1 mm), the Fourier-transform reflectance or transmittance spectroscopy technique is used. The results are supplemented by the results of ellipsometry in the wavelength range of 190 nm – 2.5 μm (4000-52 000 cm^-1).

Optical spectroscopy is also an important tool in the study of superconductors. The opening of the superconducting (SC) gap is manifested in the optical spectra in the far IR range. Analysis of the spectra allows one to determine the most important parameters of the superconducting condensate, such as the size and number of SC gaps and their anisotropy, the plasma frequencies, the penetration depth of the magnetic field, and the superfluid density.

Bruker Optics IFS125HR high resolution Fourier-transform infrared spectrometer.

Woollam VASE spectral ellipsometer with Janis CRF 725V high-vacuum cryostat.

(a) Experimental wide-range reflectance spectra of the Ba(Fe0.95Ni0.05)2As2 film at various temperatures. The dashed lines show the result of the Drude–Lorentz fit. The inset shows in detail the increase in IR reflectance in the region of 60 cm-1 associated with the superconducting transition in the film. (b) Optical conductivity data together with the results of decomposition into components within the Drude–Lorentz model at temperatures of 4, 20 and 50 K, respectively. The “noisy” regions below 55 cm-1 and above 4000 cm-1 were obtained directly from the terahertz spectroscopy and ellipsometry data, respectively. The red dashed-dotted lines demonstrate the opening of the superconducting gaps.

Optical studies of Ba(Fe_1-xNi_x)₂As₂ Films

The optical and hidden transport properties of thin films of the high-temperature superconductor Ba(Fe_1-xNi_x)₂As₂ (x = 0.035, T_c = 21.1K; x = 0.045, T_c = 20K; x = 0.05, T_c = 21.6K; x = 0.08, T_c = 10.3K) were studied in a wide spectral range of 10 – 50 000 cm^-1 using terahertz spectroscopy, infrared Fourier-transform reflectance spectroscopy and spectral ellipsometry at temperatures of 4-300K. The values of superconducting gaps and other parameters of the SC state (temperature dependences of the optical conductivity, London penetration depth, SC plasma frequencies and superfluid density), as well as the temperature dependences of such parameters of the normal state as optical conductivities, plasma frequencies and scattering rates were determined. Fermi-liquid behavior is demonstrated for optimally doped (x = 0.045, 0.05) and overdoped (x = 0.08) films, while underdoped films (x = 0.035) are characterized by non-Fermi-liquid behavior. A simple three-band Eliashberg model is used to analyze the experimental data, assuming the formation of Cooper pairs due to antiferromagnetic spin fluctuations. The temperature dependence of the resistivity of the films is analyzed within the Allen’s model generalized for multiband systems. Comparison of the determined SC gaps for Ni-Ba122 with other iron-based pnictides Co-Ba122 and Pt-Ba122 with the same level of electron doping shows that the same quantity of the similar dopant in these compounds have the analogous effect on the critical temperature T_c and the magnitude of the SC gap, i.e., the mechanism of superconductivity in these compounds is robust against the change of dopants with similar properties and not prone to fine tuning.

Journal of Physics and Chemistry of Solids, Vol. 196 112364 (2025).
Solid State Sciences,Vol. 160 107787 (2025).

Electronic band structure vs intrinsic antisite doping in the MBE grown films MnTe∙Bi_(2-x)Te_3(1-x/2)(0≤x<2): Evidence from spectroscopic ellipsometry and infrared studies

The intrinsic antisite defects, which cause doping in the antiferromagnetic topological insulators of the MnTe∙Bi₂Te₃ (n=1, 2, 3, …) family, prevent the exploration of the Dirac states affecting the Fermi level (E_F) position and magnetic properties. In the present study, the MnTe∙Bi_(2-x)Te_3(1-x/2)films grown by the MBE technique onto Si(111) substrates with increasing the Bi and Te content from MnTe to MnBi₂Te₄ were investigated by 0.5-6.5 eV spectroscopic ellipsometry. In addition, the infrared (IR) reflectance and transmittance spectra were examined. The measured ellipsometric angles, Ψ(ω) and Δ(ω), were simulated in a two- or three-layer Gaussian models. As a result, the spectra of the complex dielectric function, ε*(ω) = ε₁(ω) + iε₂(ω), the complex index of refraction, n*(ω) = n(ω) + ik(ω), and the optical conductivity σ₁(ω) were determined. We found that the absolute values of the ε₁(ω) and ε₂(ω), increased with increasing the Bi and Te content from MnTe to MnBi₂Te₄, while the ε₂(ω) maximum progressively shifts to lower photon energies from ~3.7 eV to ~1.2 eV, peculiar of the end-point compounds. At the same time, the stoichiometric MnBi₂Te₄ film exhibits the emergent Drude-type contribution in the far-IR range associated with the intrinsic antisite doping. However, the charge carrier contribution is suppressed in the MnTe∙Bi_(2-x)Te_3(1-x/2) films with the reduced Bi and Te stoichiometry, the latter being also responsible for the electronic band structure reconstruction and pronounced redistribution of the optical spectral weight.

N. N. Kovaleva et al. Appl. Phys. Lett. 125, 262404 (2024).

Control of Mooij correlations at the nanoscale in the disordered metallic Ta-nanoisland FeNi multilayers

Localisation phenomena in highly disordered metals close to the extreme conditions determined by the Mott-Ioffe-Regel (MIR) limit when the electron path is approximately equal to the interatomic distance is a challenging problem. Here, to shed light on these localization phenomena, we studid the dc transport and optical conductivity properties of nanoscaled multilayered films composed of disordered metallic Ta and magnetic FeNi nanoisland layers, where ferromagnetic FeNi nanoilands giant magnetic moments are interacting due to the indirect exchange forces acting via the Ta electron subsystem. We discovered that the localization phenomena in the disordered Ta layer lead to a decrease in the Drude contribution of free charge carriers and the appearance of the low-energy electronic excitations in the 1-2 eV spectral range, characteristic of electronic correlations, which may accompany the formation of electronic inhomogeneities. From the consistent results of the dc transport and optical studies we found that with increase in the FeNi layer thickness across the percolation threshold evolution from the superferromagetic to ferromagnetic behavior within the FeNi layer leads to the delocalization of Ta electrons from the associated localized electronic states. On the contrary, we discovered that when FeNi layer is discontinuous and represented by randomly distributed superparamagnetic FeNi nanoislands, the Ta layer normalised dc conductivity falls down below the MIR limit by about 60%. The discovered effect leading to the dc conductivity fall below the MIR limit can be associated with non-ergodicity and purely quantum (many-body) localization phenomena, which need to be challenged further.

N. N. Kovaleva et al. Sci. Rep. 10, 21172 (2020).

Yurii A. Aleshchenko, Andrey V. Muratov, Elena S. Zhukova, Lenar S. Kadyrov, Boris P. Gorshunov, Giovanni A. Ummarino, Ilya A. Shipulin “THz optical response of Ba(FeNi)As films analyzed within the three-band Eliashberg s-wave model” Journal of Physics and Chemistry of Solids, Vol. 196 112364 (2025) https://doi.org/10.1016/j.jpcs.2024.112364
Yurii A. Aleshchenko, Andrey V. Muratov, Elena S. Zhukova, Lenar S. Kadyrov, Boris P. Gorshunov, Giovanni A. Ummarino, Ilya A. Shipulin “Optical and transport properties of Ba(FeNi)As films” Solid State Sciences Vol. 160 107787 (2025) https://doi.org/10.1016/j.solidstatesciences.2024.107787
Kovaleva N. N., “Fingerprints of Mott-Hubbard physics in optical spectra of antiferromagnetic LaTiO3”, J. Alloys Compd. Vol. 976, 173192 (2024) https://doi.org/10.1016/j.jallcom.2023.173192
N. N. Kovaleva, D. Chvostova; A. V. Muratov, T. N. Fursova, S. I. Bozhko, Yu. A. Aleshchenko, A. Dejneka, K. I. Kugel, D. V. Ishchenko, O. E. Tereshchenko “Electronic band structure vs intrinsic antisite doping in the MBE grown films MnTe Bi(2−x)Te3(1−x/2) (0 x < 2): Evidence from spectroscopic ellipsometry and infrared studies” Appl. Phys. Lett. Vol. 125 Iss. 26 262404 (2024) https://doi.org/10.1063/5.0238665
В. С. Кривобок, Г. Н. Ерошенко, А. В. Муратов, С. Н. Николаев, А. В. Клековкин, И. И. Минаев, К. А. Савин, Д. А. Пашкеев, А. Р. Дубовая, Ю. А. Алещенко, С. И. Ченцов, “ Одноэлектронный спектр короткопериодной InAs/GaSb сверхрешетки с интерфейсной компенсацией напряжений ”, пЖЭТФ т.120 вып.5 с.354-358 2024 https://doi.org/10.31857/S0370274X24090069
E.V. Tarkaeva, V.A. Ievleva, A.I. Duleba, A.V. Muratov, A.M. Ionov, S.G. Protasova, A. Yu. Kuntsevich, “Amorphous VOx films with a high temperature coefficient of resistance for bolometric applications grown by reactive e-beam evaporation of V metal”, Opt. Mater. Vol 151 115378 (2024) https://doi.org/10.1016/j.optmat.2024.115378
Sergey I. Kudryashov, Pavel A. Danilov, Victor G. Vins, Evgeny V. Kuzmin, Andrey V. Muratov, Nikita A. Smirnov, Daniil A. Pomazkin, Peter P. Paholchuk, Evgeny A. Vasil’ev, Alexey N. Kirichenko, Alexey V. Gorevoy, Nikolay B. Rodionov, “Intrapulse in situ Raman probing of electron, phonon and structural dynamics in synthetic diamond excited by ultrashort laser pulses: Insights into atomistic structural damage”, Carbon, Vol. 217 118606 (2024) https://doi.org/10.1016/j.carbon.2023.118606
Kovaleva N. N., “Lattice-dynamics study of Raman-active modes in LaTiO3”, Phys. Lett. A, Vol. 479, 128942 (2023) https://doi.org/10.1016/j.physleta.2023.128942
Sergey I. Kudryashov, Victor G. Vins, Pavel A. Danilov, Evgeny V. Kuzmin, Andrey V. Muratov, Galina Yu. Kriulina, Jiajun Chen, Alexey N. Kirichenko, Yulia S. Gulina, Sergey A. Ostrikov, Peter P. Paholchuk, Michael S. Kovalev, Nikolay B. Rodionov, Alexey O. Levchenko, “Permanent optical bleaching in HPHT-diamond via aggregation of C- and NV-centers excited by visible-range femtosecond laser pulses”, Carbon Vol. 201 pp 399-407 (2023) https://doi.org/10.1016/j.carbon.2022.09.040
Sergey Kudryashov, Elena Rimskaya, Evgeny Kuzmin, Galina Kriulina, Victoria Pryakhina, Andrey Muratov, Roman Khmelnitskii, Evgeny Greshnyakov, Pavel Danilov and Vladimir Shur, “Advanced Mapping of Optically-Blind and Optically-Active Nitrogen Chemical Impurities in Natural Diamonds” Chemosensors 11(1) 24 (2023) https//doi.org/10.3390/chemosensors11010024
Sergey Kudryashov, Pavel Danilov, Evgeny Kuzmin, Nikita Smirnov, Alexey Gorevoy, Victor Vins, Daniil Pomazkin, Petr Paholchuk, Andrey Muratov, Alexey Kirichenko, Nikolay Rodionov and Evgeny Vasil’ev, “Productivity of Concentration-Dependent Conversion of Substitutional Nitrogen Atoms into Nitrogen-Vacancy Quantum Emitters in Synthetic-Diamond by Ultrashort Laser Pulses” Micromachines 14(7) 1397 (2023) https://doi.org/10.3390/mi140713975 ЖЭТФ
Sergey Vyatkin, Pavel Danilov, Nikita Smirnov, Daniil Pomazkin, Evgeny Kuzmin, Alexey Gorevoy, Andrey Muratov, Ivan Matyaev and Sergey Kudryashov, “Electron Paramagnetic Resonance Sensing of «Hidden» Atomistic and Cooperative Defects in Femtosecond Laser-Inscribed Photoluminescent Encoding Patterns in Diamond Photonics” Photonics 10(9) 979 (2023) https://doi.org/10.3390/photonics10090979
N. E. Sluchanko, E. S. Zhukova, L. N. Alyabyeva, B. P. Gorshunov, A. V. Muratov, Yu. A. Aleshchenko, A. N. Azarevich, M. A. Anisimov, N. Yu. Shitsevalova, S. E. Polovets & V. B. Filipov “Collective and Quasi-Local Modes in the Optical Spectra of YB6 and YbB6 Hexaborides with Jahn–Teller Structural Instability”, JETP vol 136 No 2 p 148 (2023) https://doi.org/10.1134/S1063776123020061

Publications

N.N. Kovaleva, O.E. Kusmartseva, A. Maljuk, Raman Scattering Study and Lattice-Dynamics Calculations in YTiO3: Precursor of the Magnetic Phase Transition in the Phonon Anomalies, Physics Letters A 430, 127985-1-7 (2022) DOI:10.1016/j.physleta.2022.127985
N. Kovaleva, D. Chvostova, L. Fekete, A. Dejneka, Bi layer properties in the Bi-FeNi GMR-type structures probed by spectrosopic ellipsometry, Coatings 12 (6), 872-1-13 (2022). DOI: 10.3390/coatings12060872
Elena S Zhukova, Aleksander Melentiev, Boris P Gorshunov, Andrey V Muratov, Yurii A Aleshchenko, Andrey Azarevich, Kirill Krasikov, Natalya Yu. Shitsevalova, Volodymyr B Filipov and N E Sluchanko, Low-temperature infrared spectroscopy of the strongly correlated semiconductor Tm0.19Yb0.81B12 with dynamic charge stripes, J. Phys.: Condens. Matter, Vol. 34, No. 46, 465603 (2022); DOI: 10.1088/1361-648X/ac920b
Antonio Gallerati, Giovanni Modanese, Giovanni Alberto Ummarino and Yurii Aleshchenko, Editorial: Interaction Between Macroscopic Quantum Systems and Gravity, Frontiers in Physics, 10:1058690 (2022); DOI: 10.3389/fphy.2022/1058690
Oleg Klimenko, Simone Schuler, Andrey Muratov, Vyacheslav Semenenko, Evgeny Gorbachev, Thomas Mueller, and Vasili Perebeinos. Tunable graphene plasmons in nanoribbon arrays: the role of interactions. Optical Materials Express 11 (5), 1390-1400 (2021)
Yu A Aleshchenko, A V Muratov, G A Ummarino, S Richter, A Anna Thomas and R Hühne. Optical and hidden transport properties of BaFe1.91Ni0.09As2 film. J. Phys.: Condens. Matter, 33 (4), 45601 (2021)
Г.В. Тихоновский, Е.А. Попова-Кузнецова, Ю.А. Алещенко, С.М. Климентов, А.В. Кабашин, А.А. Попов, Влияние кислорода на коллоидную стабильность лазерно-синтезированных наночастиц нитрида титана, Краткие сообщения по физике ФИАН №7, 36-43 (2021).
N. N. Kovaleva, D. Chvostova, O. Pacherova, A. V. Muratov, L. Fekete, I. A. Sherstnev, K. I. Kugel, F. A. Pudonin and A. Dejneka “Bismuth layer properties in the ultrathin Bi–FeNi multilayer films probed by spectroscopic ellipsometry” Appl. Phys. Lett. 119 (18), 183101 (2021)
Elena S. Zhukova, Hongbin Zhang, Victor P. Martovitskiy, Yurii G. Selivanov, Boris P. Gorshunov and Martin Dressel. Infrared Optical Conductivity of Bulk Bi2Te2Se. Crystals 2020, 10, 553; doi:10.3390/cryst10070553
Dmytro L. Kamenskyi, Artem V. Pronin, Hadj M. Benia, Victor P. Martovitskii, Kirill S. Pervakov and Yurii G. Selivanov. Bulk Cyclotron Resonance in the Topological Insulator Bi2Te3. Crystals 2020, 10, 722; doi:10.3390/cryst10090722
V. A. Yakovlev , S. Schreyeck , A. V. Muratov, I. V. Kucherenko, V. S. Vinogradov, N. N. Novikov , G. Karczewski , Yu. A. Aleshchenko, S. Chusnutdinow. “Temperature Dependence of the Vibrational Mode of Pb1-xSnxTe Films Grown by MBE on the GaAs/CdTe Hybrid Substrate”, BULLETIN OF THE LEBEDEV PHYSICS INSTITUTE, vol. 47 iss. 1 pp 16-22 (2020) DOI: 10.3103/S106833562001008X
V.A. Yakovlev, A.V. Muratov, I.V. Kucherenko, V.S. Vinogradov , N.N. Novikova, G. Karczewski, S. Schreyeck “Structural phase transition and manifestation of eddy currents in IR reflection spectra of PbSnTe semiconductor films”, QUANTUM ELECTRONICS, vol. 50 iss. ‏ 3 pp. ‏(2020) 263-266 DOI: 10.1070/QEL17256
Anastasiya A. Fronya, Sergey V. Antonenko, Alexander Yu. Kharin, Andrei V. Muratov , Yury A. Aleschenko , Sergey I. Derzhavin , Nikita V. Karpov , Yaroslava I. Dombrovska , Alexander A. Garmash , Nikolay I. Kargin , Sergey M. Klimentov , Victor Yu. Timoshenko and Andrei V. Kabashin “Tailoring Photoluminescence from Si-Based Nanocrystals Prepared by Pulsed Laser Ablation in He-N-2 Gas Mixtures”, MOLECULES, vol. 25 iss. 3 p 440 (2020). DOI: 10.3390/molecules25030440
G.A. Ummarino, A.V. Muratov, L.S. Kadyrov, B.P. Gorshunov, S. Richter, A. Anna Thomas, R. H¨uhne and Yu.A. Aleshchenko, “THz electrodynamics of BaFe1.91Ni0.09As2 film analyzed in the framework of multiband Eliashberg theory”, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, vol. 33, iss. 7, 075005 (2020) DOI: 10.1088/1361-6668/ab87ae
Aleshchenko, Yurii, Boris Gorshunov, Elena Zhukova, Andrey Muratov, Alexander Dudka, Rajendra Dulal, Serafim Teknowijoyo, Sara Chahid, Vahan Nikoghosyan, and Armen Gulian. “Possible superconductivity above 40 K in rhenium-doped strontium ruthenates indicated by Fourier-transform infrared spectroscopy.” Phys. Rev. Research 2, 042020(R) (2020) DOI:https://doi.org/10.1103/PhysRevResearch.2.042020
Aleshchenko, Y. A., Muratov, A. V., Ummarino, G. A., Richter, S., Thomas, A. A., Hühne, R. (2020). Optical and hidden transport properties of BaFe1. 91Ni0. 09As2 film. Journal of Physics: Condensed Matter, 33(4), 045601.(2021) DOI: https://doi.org/10.1088/1361-648X/abbc33
N. N. Kovaleva; F. V. Kusmartsev; A. B. Mekhiya; I. N. Trunkin; D. Chvostova; A. B. Davydov; L. N. Oveshnikov; O. Pacherova; I. A. Sherstnev; A. Kusmartseva; K. I. Kugel; A. Dejneka; F. A. Pudonin; Y. Luo; B. A. Aronzon, Control of Mooij correlations at the nanoscale in the disordered metallic Ta – nanoisland FeNi multilayers. Scientific reports 10, 21172 (2020). DOI:10.1038/S41598-020-78185-6
Kovaleva, N., Fekete, L., Chvostova, D., Muratov, A. Morphology and Optical Properties of Thin Cd3As2 Films of a Dirac Semimetal Compound. Metals, 10(10), 1398 (2020). DOI: 10.3390/MET10101398
Ia. A. Mogunov, S. Lysenko, F. Fernández, A. Rúa, A. V. Muratov, A. J. Kent, A. M. Kalashnikova, and A. V. Akim, Photoelasticity of VO2 nanolayers in insulating and metallic phases studied by picosecond ultrasonics, Phys. Rev. Materials 4, 125201 (2020) DOI:https://doi.org/10.1103/PhysRevMaterials.4.125201