arXiv subjects

G. G. Kozlov

Publications and source records attributed to G. G. Kozlov.

At least 19 recordsLinked to original sources

arXiv2025

Spin noise reveals spin dynamics and recharging of lead halide perovskite nanocrystals

The lead halide perovskite nanocrystals embedded into a glass matrix exhibit strong interaction with light and demonstrate exceptional optical and spin related features along with long-term chemical and physical stability. We apply the spin noise spectroscopy technique which offers a number of specific opportunities to study the spin system of CsPbI$_3$ nanocrystals in a fluorophosphate glass matrix. A pronounced spin precession peak with an isotropic $g$-factor absolute value of 2.7 and record dephasing time of T$_{2\text{,e}}$ = 2.7 ns is ascribed to resident electrons in the perovskite nanocrystals. The experimentally observed Faraday rotation noise with no noise of ellipticity is explained by saturation of the inhomogeneously broadened optical transition. Increasing the probe intensity, we went beyond the non-perturbative regime and observed a number of light-induced effects. In particular, the illumination with shorter wavelength light gives rise to a persistent recharging of the quantum dots by holes ($|g|=0.17$ and T$^*_{2\text{,h}}$ = 1.4 ns, T$^*_{1\text{,h}}$ $\geq$ 30 ns), which remains stable over multiple cycles of heating to the room temperature and cooling. In addition, elliptically polarized light induced an "optical" magnetic field on the system due to the AC Stark effect. It is confirmed using a new modification of polarization noise spectroscopy with a small degree of circular polarization of the probe light added with different frequencies.

cond-mat.mes-hall↗

arXiv2025

Magnetic quadrupole dichroism in isotropic medium

For isotropic media, the magnetic field applied across the light propagation direction affects their optical properties only in the second order, and its effect proves to be much weaker than in the longitudinal field. In this work, we show that, under resonant excitation well beyond the linear regime, the situation changes drastically: A small magnetic linear anisotropy considerably increases, and an even stronger new quadrupole dichroism emerges. The latter manifests itself as the 90$^\circ$-periodic azimuthal dependence of the transmission and anisotropic rotation of the probe polarization plane. These effects are described microscopically in a toy model, and their symmetry analysis is presented. Both are observed experimentally on the D2 resonance of cesium vapor and agree with the theoretical predictions. The large magnitude of the quadrupole dichroism makes it promising for magnetometric applications and for studying the effects of anisotropic bleaching.

physics.optics↗

arXiv2024

Measuring spin-noise correlation function via time reversal

We propose a simple method of measuring the autocorrelation function of a spin noise based on multiplication and averaging two digitized signal traces, with one of them being a time-reversed copy of the other. This procedure allows one to obtain, with lower computational expenses, all the information usually derived in the Fourier transform spin-noise spectroscopy, retaining all the merits of the latter. We successfully applied this method to the measurements of spin noise in cesium vapors by using a digital oscilloscope in the capacity of the analog-to-digital converter. Specific opportunities of this experimental approach as applied to a more general problem of studying the nature of light-intensity noise are discussed.

quant-ph↗

arXiv2023

Spin noise of a halide perovskite

We report on first observation of spin noise in a strongly birefringent semiconductor -- halide perovskite single crystal MAPbI$_3$. The observed spin noise resonance is ascribed to free holes with a record spin dephasing time of 4 ns. The spin dynamics is found to be affected by the residual light absorption of the crystal providing renormalization of the Larmor frequency. Extended spin noise spectroscopy with rotating magnetic field allowed us not only to evaluate the $g$-factor anisotropy, but also to distinguish two different spin subsystems tentatively associated to twinning of the crystal.

cond-mat.mes-hall↗

arXiv2023

Optically driven spin-alignment precession

The effect of optically driven spin precession discovered by Bell and Bloom [W. E. Bell and A. L. Bloom, Phys. Rev. Lett. 6, 280 (1961)] is widely used nowadays as a basis for numerous experiments in fundamental physics and for diverse applications. In this paper we consider a much less popular version of the light-induced spin precession that does not imply coherent precession of the spin-system magnetization and is excited by linearly (rather than circularly) polarized light. Pump-probe measurements performed on the D2 line of cesium vapor show that the magnitude of the signal of the optically driven spin-alignment precession, in "vacuum" cells (with no buffer gas) is close to that of classical spin-orientation precession. In the presence of buffer gas, however, the signal of spin-alignment precession appears to be strongly suppressed. The discovered effect is ascribed to spin mixing of excited states of cesium atoms in the cycle of optical pumping.

physics.atom-ph↗

arXiv2023

Optically stimulated electron paramagnetic resonance: simplicity, versatility, information content

A simple technique for observing optically stimulated electron paramagnetic resonance (OSEPR) is proposed and investigated. The versatility and information content of the described technique is demonstrated by the example of the OSEPR spectra of systems that are unpopular for this type of spectroscopy: a crystal with rare-earth ions Nd$^{3+}$ and a doped semiconductor GaAs. In addition, the OSEPR spectrum of atomic cesium is presented, in which an optical nonlinearity is observed that makes it possible to estimate the Rabi frequency for the relevant optical transition. The effects observed in the described experiments (switching of peaks to dips, light-induced splitting of the OSEPR lines, and the appearance of a spectral feature at the double-Larmor frequency) are interpreted using the model proposed in the theoretical part of the work. The suggested interpretation shows the possibility of using the described OSEPR technique to estimate not only `magnetic' parameters of the model Hamiltonian (g-factors, spin relaxation times), but also the Rabi frequencies characterizing optical transitions.

physics.optics↗

arXiv2023

Spontaneous noise of birefringence in rare-earth doped glasses

We report on first direct observation of spontaneous fluctuations of birefringence in glasses doped with rare-earth (RE) ions. The fluctuations were observed in Nd$^{3+}$- and Yb$^{3+}$-doped glasses as polarization noise of the laser beam transmitted through the sample in the region of the RE-ion absorption. The noise was characterized by a flat (``white'') spectrum in the range of frequencies up to 1 GHz and did not show any dependence on magnetic field. The discovered polarization noise is interpreted in terms of structural dynamics of glasses revealed at low temperatures and usually described in the model of tunneling two-level systems (TLS). High sensitivity of the polarization noise technique to this dynamics is related to small homogeneous width of \textit{f-f} transitions of RE-ions in glasses and small spectral width of the probe laser light. The discovered effect provides a new experimental approach to studying low-temperature structural dynamics of different disordered matrices and interactions of impurities with environment in such media.

cond-mat.dis-nn↗

arXiv2022

Spin noise in birefringent and inhomogeneous media

It is known that linear birefringence of the medium essentially hinders measuring the Faraday effect. For this reason, optically anisotropic materials have never been considered as objects of the Faraday-rotation-based spin noise spectroscopy (SNS). We show, both theoretically and experimentally, that strong optical anisotropy that may badly suppress the regular Faraday rotation of the medium, practically does not affect the measurement of the spatially uncorrelated spin fluctuations. An important consequence of this result is that the Faraday-rotation noise should be also insensitive to spatially nonuniform birefringence, which makes the SNS applicable to a wide class of optically anisotropic and inhomogeneous materials. We also show that the birefringent media provide additional opportunity to measure spatial spin correlations. Results of the experimental measurements of the spin-noise spectra performed on 4$f$--4$f$ transitions of Nd$^{3+}$ ions in the CaWO$_4$ and LiYF$_4$ crystals well agree with the theory.

cond-mat.mes-hall↗

arXiv2021

Nonlinear Faraday effect and spin noise in rare-earth activated crystals

The spin-noise spectroscopy (SNS) method implies high efficiency of conversion of the spin-system magnetization to the Faraday rotation angle. Generally, this efficiency cannot be estimated using the characteristics of the regular magneto-optical activity of a paramagnet. However, it may be drastically enhanced in systems with strong inhomogeneous broadening of the optical transitions. This enhancement leads to the giant spin-noise gain effect and previously allowed one to apply the SNS to rare-earth-activated crystals. We show that the nonlinear resonant Faraday effect can be used to measure the homogeneous width of the inhomogeneously broadened transition and, thus, to estimate the applicability of the SNS to this type of paramagnet. We present the theoretical description of the effect and perform measurements on intraconfigurational ($4f$-$4f$) transitions of the trivalent rare-earth ions of neodymium and ytterbium in fluorite-based crystals. The proposed experimental approach establishes new links between the effects of nonlinear optics and spin-noise characteristics of crystals with paramagnetic impurities and offers new ways of research in the physics of impurity crystals.

cond-mat.mes-hall↗

arXiv2021

Invariants in the paramagnetic resonance spectra of impurity crystals

We show that in cubic crystals with anisotropic impurity centers the sum of squares of the magnetic resonance (EPR) frequencies is invariant with respect to the magnetic field direction. The connection between such an invariant and the g-tensor components of the impurity is derived for different types of centers. The established regularity is confirmed experimentally for the spin-noise spectra of a CaF2-Nd3+ crystal. We show how this property of the EPR spectra can be efficiently used for the assignment of paramagnetic centers in cubic crystals.

cond-mat.mes-hall↗

arXiv2021

Anomalous light-induced broadening of the spin-noise resonance in cesium vapor

We uncover a highly nontrivial dependence of the spin-noise (SN) resonance broadening induced by the intense probe beam. The measurements were performed by probing the cell with cesium vapor at the wavelengths of the transition ${6}^2S_{1/2} \leftrightarrow {6}^2P_{3/2}$ ($\mathrm{D}_2$ line) with the unresolved hyperfine structure of the excited state. The light-induced broadening of the SN resonance was found to differ strongly at different slopes of the $\mathrm{D}_2$ line and, generally, varied nonmonotonically with light power. We discuss the effect in terms of the phenomenological Bloch equations for the spin fluctuations and demonstrate that the SN broadening behavior strongly depends on the relation between the pumping and excited-level decay rates, the spin precession, and decoherence rates. To reconcile the puzzling experimental results, we propose that the degree of optical perturbation of the spin-system is controlled by the route of the excited-state relaxation of the atom or, in other words, that the act of optical excitation of the atom does not necessarily break down completely its ground-state coherence and continuity of the spin precession. Spectral asymmetry of the effect, in this case, is provided by the position of the "closed" transition $F = 4 \leftrightarrow F' = 5$ at the short-wavelength side of the line. This hypothesis, however, remains to be proven by microscopic calculations.

physics.optics↗

arXiv2021

Nonlinear spectroscopy of high-spin fluctuations

We investigate theoretically and experimentally fluctuations of high spin (F>1/2) beyond the linear response regime and demonstrate dramatic modifications of the spin noise spectra in the high power density probe field. Several effects related to an interplay of high spin and perturbation are predicted theoretically and revealed experimentally, including strong sensitivity of the spin noise spectra to the mutual orientation of the probe polarization plane and magnetic field direction, appearance of high harmonics of the Larmor frequency in the spin noise and the fine structure of the Larmor peaks. We demonstrate the ability of the spin-noise spectroscopy to access the nonlinear effects related to the renormalization of the spin states by strong electromagnetic fields.

physics.atom-ph↗

arXiv2021

Raman scattering model of the spin noise

The mechanism of formation of the polarimetric signal observed in the spin noise spectroscopy (SNS) is analyzed from the viewpoint of the light scattering theory. A rigorous calculation of the polarimetric signal (Faraday rotation or ellipticity) recorded in the SNS is presented in the approximation of single scattering. We show that it is most correctly to consider this noise as a result of scattering of the probe light beam by fluctuating susceptibility of the medium. Fluctuations of the gyrotropic (antisymmetric) part of the susceptibility tensor lead to appearance of the typical for the SNS Faraday rotation noise at the Larmor frequency. At the same time, fluctuations of linear anisotropy of the medium (symmetric part of the susceptibility tensor) give rise to the ellipticity noise of the probe beam spectrally localized at the double Larmor frequency. The results of the theoretical analysis well agree with the experimental data on the ellipticity noise in cesium vapor.

physics.optics↗

arXiv2020

Spin noise signatures of the self-induced Larmor precession

Bose-Einstein condensates of exciton-polaritons are known for their fascinating coherent and polarization properties. The spin state of the condensate is reflected in polarization of the exciton-polariton emission, with temporal fluctuations of this polarization being, in general, capable of reflecting quantum statistics of polaritons in the condensate. To study the polarization properties of optically trapped polariton condensates, we take advantage of the spin noise spectroscopy technique. The ratio between the noise of ellipticity of the condensate emission and its polarization plane rotation noise is found to be dependent, in a nontrivial way, on the intensity of CW nonresonant laser pumping. We show that the interplay between the ellipticity and the rotation noise can be explained in terms of the competition between the self-induced Larmor precession of the condensate pseudospin and the static polarization anisotropy of the microcavity.

cond-mat.mes-hall↗

arXiv2020

Polarimetric observation of noise of linear birefringence of cesium atomic vapors spectrally localized at double Larmor frequency in a magnetic field

We study radio-frequency spectrum of ellipticity noise of a probe laser beam transmitted through a cell with cesium vapor in a magnetic field. The experimental results are interpreted in terms of the model proposed by Gorbovitskii and Perel (Opt. Spektrosc. 54, 388 (1983)) according to which the observed noise arises due to heterodyning of the light scattered by fluctuations of the tensor $ α$ of optical susceptibility of cesium vapor. We show, both experimentally and theoretically, that, in the noise measurements if this kind, along with fluctuations of the antisymmetric (gyrotropic) part of the tensor $ α$ at the Larmor frequency, may be observed fluctuations of its symmetric part, corresponding to fluctuations of linear birefringence (alignment) of the atomic system. The polarization noise provided by these fluctuations is localized spectrally at the double Larmor frequency.

physics.atom-ph↗

arXiv2019

Gigantic spin-noise gain enables magnetic resonance spectroscopy of impurity crystals

Spin noise spectroscopy is a method of magnetic resonance widely used, nowadays, in atomic and semiconductor research. Classical objects of the EPR spectroscopy - dielectrics with paramagnetic impurities - seemed to be unsuitable for this technique because of large widths of allowed optical transitions and, therefore, low specific Faraday rotation (FR). We show, however, that the FR noise detected at the wavelength of a weak optical transition (with low regular FR) may increase by many orders of magnitude as its homogeneous width decreases. This spin-noise gain effect, numerically described by the ratio of the inhomogeneous linewidth to homogeneous, relates primarily to forbidden intraconfigurational transitions of impurity ions with unfilled inner electronic shells. Specifically, for the f-f transitions of rare-earth ions in crystals, this factor may reach 10$^8$. In this paper, we report on the first successful application of spin noise spectroscopy for detecting magnetic resonance of rare-earth ions in crystals.

cond-mat.mes-hall↗

arXiv2019

Spin-alignment noise in atomic vapor

In the conventional spin noise spectroscopy, the probe laser light monitors fluctuations of the spin orientation of a paramagnet revealed as fluctuations of its gyrotropy, i.e., circular birefringence. For spins larger than 1/2, there exists spin arrangement of a higher order---the spin alignment---which also exhibits spontaneous fluctuations. We show theoretically and experimentally that the alignment fluctuations manifest themselves as the noise of the linear birefringence. In a magnetic field, the spin-alignment fluctuations, in contrast to those of spin orientation, show up as the noise of the probe-beam ellipticity at the double Larmor frequency, with the most efficient geometry of its observation being the Faraday configuration with the light propagating along the magnetic field. We have detected the spin-alignment noise in a cesium-vapor cell probed at the wavelength of D2 line (852.35 nm). The magnetic-field and polarization dependence of the ellipticity noise are in full agreement with the developed theory.

physics.atom-ph↗

arXiv2019

Detection and amplification of spin noise using scattered laser light in a quantum-dot microcavity

Fundamental properties of the spin-noise signal formation in a quantum-dot microcavity are studied by measuring the angular characteristics of the scattered light intensity. A distributed Bragg reflector microcavity was used to enhance the light-matter interaction with an ensemble of n-doped (In,Ga)As/GaAs quantum dots, which allowed us to study subtle effects of the noise signal formation. Detecting the scattered light outside of the aperture of the transmitted light, we measured the basic electron spin properties, like g-factor and spin dephasing time. Further, we investigated the influence of the microcavity on the scattering distribution and possibilities of signal amplification by additional resonant excitation.

cond-mat.mes-hall↗