Pavel Bazhin
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RESEARCH, TEACHING, or OTHER INTERESTS
Condensed Matter Physics
Scopus Publications
- Dynamic polarization of nuclear spins by optically oriented electrons and holes in lead halide perovskite semiconductors
Mladen Kotur, Pavel S. Bazhin, Kirill V. Kavokin, Nataliia E. Kopteva, Dmitri R. Yakovlev, Dennis Kudlacik, Manfred Bayer
Physical Review B, 2026
A theory of dynamic polarization of the nuclear spin system via optically-oriented charge carriers in lead halide perovskites is developed and compared with the experiments performed on a FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$ crystal. The spin Hamiltonians of the electron and hole hyperfine interaction with the nuclear spins of lead and halogen are derived. The hyperfine interaction of the halogen spins with charge carriers is shown to be anisotropic and depending on the position of the halogen nucleus in the cubic elementary cell. The quadrupole splitting is absent for the lead spins, but plays an important role for the halogen spins and affects their dynamic polarization by charge carriers. The Overhauser fields of the dynamically polarized nuclei are calculated as functions of the tilting angle of an external magnetic field and compared with the experimentally measured angular dependence of the Hanle effect. The comparison of the theoretical model with the experimental data reveals an enhanced spin polarization of the lead nuclei, whose mean spin exceeds several times the mean spins of localized electrons and holes. This unexpectedly strong spin polarization is explained by the interaction of the lead nuclei with excitons having a high degree of spin orientation due to their short lifetime after excitation by circularly-polarized light. The dynamic polarization of the quadrupole-split halogen spins manifests itself via the magnetic field they produce at the lead nuclei. This field maintains the magnetization of the lead nuclei at zero external magnetic field. The dynamics of the nuclear spin polarization is measured under optical pumping and in the dark, yielding a nuclear spin-lattice relaxation time on the order of 10 seconds. - Nuclear spin-spin interactions in CdTe probed by zero-and ultralow-field optically detected NMR
V. M. Litvyak, P. S. Bazhin, R. André, M. Vladimirova, K. V. Kavokin
Physical Review B, 2024
Nuclear magnetic resonance (NMR) is particularly relevant for studies of internuclear spin coupling at zero and ultra-low fields (ZULF), where spin-spin interactions dominate over Zeeman ones. Here we report on ZULF NMR in CdTe. In this semiconductor all magnetic isotopes have spin $I = 1/2$, so that internuclear interactions are never overshadowed by quadrupole effects. Our experiments rely on warm-up spectroscopy, a technique that combines optical pumping, additional cooling via adiabatic demagnetisation, and detection of the oscillating magnetic field-induced warm-up of the nuclear spin system via Hanle effect. We show that NMR spectra exhibit a rich fine structure, consistent with the low abundance of magnetic isotopes in CdTe, their zero quadrupole moments, as well as direct and indirect interactions between them. A model assuming that the electromagnetic radiation is absorbed by nuclear spin clusters composed of up to 5 magnetic isotopes allows us to reproduce the shape of a major part of the measured spectra. - Ionization Waves Initiating Single-Electrode Breakdown in Long Discharge Tubes
A. I. Shishpanov, V. V. Zaletov, P. S. Bazhin
Bulletin of the Lebedev Physics Institute, 2024
Abstract Ionization waves (IWs) of positive polarity are studied experimentally in several sealed discharge tubes containing neon at pressures of 0.6‒15 Torr and surrounded with a grounded metal screen. The IWs arise at the stage single-electrode breakdown development at moderate overvoltage conditions, and belong to “slow” ionization waves (velocity of 105‒108 cm/s). The wave propagation is accompanied by a monotonic loss of velocity and the electric potential magnitude at the IW front, indicating its significant spatial attenuation. The IWs are studied by recording x‒t diagrams supplemented with measurements of instantaneous velocities, front potentials, and attenuation coefficients at various pressures and applied voltages. An exponential nature of a decrease in the front potential and instantaneous velocity of the IWs with the distance traveled is established. It is found that the scales of the exponential decrease in both quantities do not coincide. The obtained results can be useful in planning experiments on breakdown in long tubes, ionization wave modeling, as well as their technological implementation - Breakdown voltage in long tubes: the effect of surface charge
A V Meshchanov, A I Shishpanov, P S Bazhin, Y Z Ionikh
Plasma Sources Science and Technology, 2022
The study focuses on ignition processes in long discharge tubes (the length of which is large compared to the diameter) in rare gases Ne, Ar, and their mixture at a low pressure (∼1 Torr). Gas breakdown was caused by ramp voltage pulses of positive or negative polarity applied to the active electrode. The breakdown voltage was determined by the voltage drop at breakdown. The emission of the ionization wave (IW) preceding the breakdown was explored. The discharge tubes were exposed to two types of external influences. The first was illumination of the tube cathode with visible spectrum light, while the second was the constant or pulsed bias of the cathode potential by a value lower than that of maintaining discharge. In both cases the breakdown voltage increased up to doubling under some conditions. The observation of the IW revealed the presence of extra waves preceding the regular pre-breakdown IW. The extra wave velocity and emission intensity differed from those of the regular waves. Their main feature is that they do not overcome the entire inter-electrode gap, but weaken and disappear in between. It is assumed that the extra waves deposit the wall surface charge, which in turn affects the breakdown voltage. The increased breakdown voltage value remains for tens of minutes, which could indicate the surface charge lifetime of the same order. This was confirmed by direct wall-potential measurements using an electrostatic voltmeter. - Low-frequency one-electrode discharge in long tubes at low gas pressure
A I Shishpanov, P S Bazhin, D O Ivanov, A V Meschanov
Plasma Research Express, 2020
One electrode discharge (OED) was studied in long tubes filled with high purity neon or argon at a pressure of 1–4 Torr. The main feature of the discharge is a low rate (less than 10 kHz) of the voltage pulses of given polarity applied to only one electrode, while another one remains free or missing. The discharge is observed as a glowing plasma column which occupies either the whole tube or its part depending on actual voltage amplitude and rate. Current-volt characteristics, ignition thresholds and the OED length changing patterns demonstrate features unknown for RF discharges. It was found that the plasma generation mechanism actually is a formation of a set of ionization waves (IW). As a result, the discharge glow as well as its current can be presented as a set of pulses with duration equal to the IW propagation time (∼1 μs) that appear with the voltage frequency. The pulse form reflects the IW structure which represents itself as a front of high electrical potential and a plasma channel linking it with the electrode. It was shown that the wave motion is characterized by an attenuation of which the patterns were investigated by the time-position diagrams method. The attenuation specifies the length of the occupied plasma area as well as other OED parameters. The proposed simplified kinematic model of the wave propagation is based on the assumption that the attenuation is caused by the IW front potential decrease which in its turn occurs due to exponential falling of electric field strength in the plasma channel. This model allows to estimate the electric field in different OED points as well as to define average electron concentration via the current measurements. Typical values of the above parameters are 5 V cm−1 · Torr and 109–1010 cm−3.
