arXiv subjects

A. Kudlis

Publications and source records attributed to A. Kudlis.

At least 37 records · Page 2Linked to original sources

arXiv2024

Kinetic theory of vacuum pair production in uniform electric fields revisited

We investigate the phenomenon of electron-positron pair production from vacuum in the presence of a uniform time-dependent electric field of arbitrary polarization. Taking into account the interaction with the external classical background in a nonperturbative manner, we quantize the electron-positron field and derive a system of ten quantum kinetic equations (QKEs) showing that the previously-used QKEs are incorrect once the external field rotates in space. We employ then the Wigner-function formalism of the field quantization and establish a direct connection between the Dirac-Heisenberg-Wigner (DHW) approach to investigating the vacuum pair-production process and the QKEs. We provide a self-contained description of the two theoretical frameworks rigorously proving their equivalence and present an exact one-to-one correspondence between the kinetic functions involved within the two techniques. Special focus is placed on the analysis of the spin effects in the final particle distributions.

hep-ph↗

arXiv2024

Theory of magnetotrion-polaritons in transition metal dichalcogenide monolayers

Magnetic field is a powerful tool for the manipulation of material's electronic and optical properties. In the domain of transition metal dichalcogenide monolayers, it allows one to unveil the spin, valley, and orbital properties of many-body excitonic complexes. Here we study theoretically the impact of normal-to-plane magnetic field on trions and trion-polaritons. We demonstrate that spin and orbital effects of a magnetic field give comparable contributions to the trion energies. Moreover, as magnetic field redistributes the free electron gas between two valleys in the conductance band, the trion-photon coupling becomes polarization and valley dependent. This results in an effective giant Zeeman splitting of trion-polaritons, in-line with the recent experimental observations.

cond-mat.mes-hall↗

arXiv2024

Pair production in rotating electric fields via quantum kinetic equations: Resolving helicity states

We investigate the phenomenon of electron-positron pair production from vacuum in the presence of a strong electric field of circular polarization. By means of a nonperturbative approach based on the quantum kinetic equations (QKEs), we numerically calculate helicity-resolved momentum distributions of the particles produced and analyze the corresponding helicity asymmetry. It is demonstrated that the external rotating field tends to generate left-handed and right-handed particles traveling in opposite directions. Generic symmetry properties of the momentum spectra are examined analytically by means of the QKEs and also confirmed and illustrated by direct numerical computations. The helicity signatures revealed in our study are expected to provide a firmer basis for possible experimental investigations of the fundamental phenomenon of vacuum pair production in strong fields.

hep-ph↗

arXiv2024

The bending rigidity exponent of a two-dimensional crystalline membrane with arbitrary number of flexural phonon modes

We investigate the elastic behavior of two-dimensional crystalline membrane embedded into real space taking into account the presence an arbitrary number of flexural phonon modes $d_c$ (the number of out-of-plane deformation field components). The bending rigidity exponent $η$ is extracted by numerical simulation via Fourier Monte Carlo technique of the system behaviour in the universal regime. This universal quantity governess the correlation function of out-of-plane deformations at long wavelengths and defines the behaviour of renormalized bending rigidity at small momentum $\varkappa~\sim~1/q^η$. The resulting numerical estimates of the exponent for various $d_c$ are compared with the numbers obtained from the approximate analytical techniques.

cond-mat.stat-mech↗

arXiv2024

All-optical control of skyrmion configuration in CrI$_3$ monolayer

The potential for manipulating characteristics of skyrmions in a CrI$_3$ monolayer using circularly polarised light is explored. The effective skyrmion-light interaction is mediated by bright excitons whose magnetization is selectively influenced by the polarization of photons. The light-induced skyrmion dynamics is illustrated by the dependencies of the skyrmion size and the skyrmion lifetime on the intensity and polarization of the incident light pulse. Two-dimensional magnets hosting excitons thus represent a promising platform for the control of topological magnetic structures by light.

cond-mat.mes-hall↗

arXiv2024

Disorder-Induced Topological Transitions in a Multilayer Topological Insulator

We examine the impact of non-magnetic disorder on the electronic states of a multilayer structure comprising layers of both topological and conventional band insulators. Employing the Burkov-Balents model with renormalized tunneling parameters, we generate phase diagrams correlating with disorder, demonstrating that non-magnetic disorder can induce transitions between distinct topological phases. The subsequent section of our investigation focuses on the scenario where disorder is unevenly distributed across layers, resulting in fluctuations of the interlayer tunneling parameter - termed off-diagonal disorder. Furthermore, we determine the density of states employing the self-consistent single-site diagram technique, expanding the Green function in relation to the interlayer tunneling parameter (locator method). Our findings reveal that off-diagonal disorder engenders delocalized bulk states within the band gap. The emergence of these states may lead to the breakdown of the anomalous quantum Hall effect (AQHE) phase, a phenomenon that has garnered significant attention from researchers in the realm of topological heterostructures. Nonetheless, our results affirm the stability of the Weyl semimetal phase even under substantial off-diagonal disorder.

cond-mat.mes-hall↗

arXiv2023

A trion in a magnetic field revisited

We revisit the problem of a two dimensional trion in an external magnetic field. We demonstrate that the approximations used previously for finding the energy spectrum of this system break down in the experimentally accessible range of magnetic fields. It is shown that the neglect of the Coulomb-induced mixing of different Landau levels corresponding to non-interacting particles leads to a strong underestimation of the trion binding energies even at extremely high magnetic fields (hundreds of Tesla). Moreover, proper account of the Coulomb effects for certain values of the parameters can lead to the appearance of additional discrete trion states which were overlooked previously. Finally, we provide a database of the matrix elements necessary for calculation of the magnetotrion spectra for a wide class of materials.

cond-mat.mes-hall↗

arXiv2023

Quantum electrodynamical density functional theory for generalized Dicke model

We formulate and analyze in detail the ground state quantum electrodynamical density functional theory (QEDFT) for a generalized Dicke model describing a collection of $N$ tight-binding dimers minimally coupled to a cavity photon mode. This model is aimed at capturing essential physics of molecules in quantum cavities in polaritonic chemistry, or quantum emitters embedded in mesoscopic resonators of the circuit QED, and, because of its simplicity, is expected to provide important insights regarding the general QEDFT. We adopt the adiabatic connection formalism and the diagrammatic many-body theory to regularly derive a sequence of explicit approximations for the exchange-correlation (xc) energy in the ground state QEDFT, and to compare their performance with the results of exact numerical diagonalization. Specifically, we analyze the earlier proposed one-photon optimized effective potential (OEP) scheme, its direct second order extensions, and a non-perturbative xc functional based on the photon random phase approximation (RPA). Our results demonstrate the excellent performance of RPA-QEDFT in the ultrastrong coupling regime, and for any number $N$ of Dicke molecules in the cavity. We study in detail the scaling of xc energy with $N$, and emphasize the importance for the ground state QEDFT of collective effects in the interaction of molecules with cavity photons. Finally, we discuss implications of our results for realistic systems.

cond-mat.mes-hall↗

arXiv2023

All-optical magnetization control in CrI$_3$ monolayers: a microscopic theory

Bright excitons in ferromagnetic monolayers CrI$_3$ efficiently interact with lattice magnetization, which makes possible all-optical resonant magnetization control in this material. Using the combination of ab-initio simulations within Bethe-Salpeter approach, semiconductor Bloch equations and Landau-Lifshitz equations, we construct a microscopic theory of this effect. Solving numerically the resulting system of the coupled equations describing the dynamics of atomic spins and spins of the excitons, we demonstrate the possibility of a tunable control of macroscopic magnetization of a sample.

cond-mat.mes-hall↗

arXiv2023

Effective exponents near bicritical points

The phase diagram of a system with two order parameters, with ${\it n_1}$ and $n_2$ components, respectively, contains two phases, in which these order parameters are non-zero. Experimentally and numerically, these phases are often separated by a first-order "flop" line, which ends at a bicritical point. For $n=n_1+n_2=3$ and $d=3$ dimensions (relevant e.g. to the uniaxial antiferromagnet in a uniform magnetic field), this bicritical point is found to exhibit a crossover from the isotropic $n$-component universal critical behavior to a fluctuation-driven first-order transition, asymptotically turning into a triple point. Using a novel expansion of the renormalization group recursion relations near the isotropic fixed point, combined with a resummation of the sixth-order diagrammatic expansions of the coefficients in this expansion, we show that the above crossover is slow, explaining the apparently observed second-order transition. However, the effective critical exponents near that transition, which are calculated here, vary strongly as the triple point is approached.

cond-mat.stat-mech↗

arXiv2023

Stability of $φ^4$-vector model: four-loop $\varepsilon$ expansion study

The stability of $O(n)$-symmetric fixed point regarding the presence of vector-field term ($\sim h p_αp_β$) in the $φ^4$ field theory is analyzed. For this purpose, the four-loop renormalization group expansions in $d=4-2\varepsilon$ within Minimal Subtraction (MS) scheme are obtained. This frequently neglected term in the action requires a detailed and accurate study on the issue of existing of new fixed points and their stability, that can lead to the possible change of the corresponding universality class. We found that within lower order of perturbation theory the only $O(n)$-symmetric fixed point $(g_{\text{H}},h=0)$ exists but the corresponding positive value of stability exponent $ω_h$ is tiny. This led us to analyze this constant in higher orders of perturbation theory by calculating the 4-loop contributions to the $\varepsilon$ expansion for $ω_h$, that should be enough to infer positivity or negativity of this exponent. The value turned out to be undoubtedly positive, although still small even in higher loops: $0.0156(3)$. These results cause that the corresponding vector term should be neglected in the action when analyzing the critical behaviour of $O(n)$-symmetric model. At the same time, the small value of the $ω_h$ shows that the corresponding corrections to the critical scaling are significant in a wide range.

cond-mat.stat-mech↗

arXiv2022

Scattering of a twisted electron wavepacket by a finite laser pulse

The behavior of a twisted electron colliding with a linearly polarized laser pulse is investigated within relativistic quantum mechanics. In order to better fit the real experimental conditions, we introduce a Gaussian spatial profile for the initial electron state as well as an envelope function for the laser pulse, so the both interacting objects have a finite size along the laser propagation direction. For this setup we analyze the dynamics of various observable quantities regarding the electron state: the probability density, angular momentum, and mean values of the spatial coordinates. It is shown that the motion of a twisted wavepacket can be accurately described by averaging over classical trajectories with various directions of the transverse momentum component. On the other hand, full quantum simulations demonstrate that the ring structure of the wavepacket in the transverse plane can be significantly distorted leading to large uncertainties in the total angular momentum of the electron. This effect remains after the interaction once the laser pulse has a nonzero electric-field area.

quant-ph↗

arXiv2022

Critical behavior of isotropic systems with strong dipole-dipole interaction: three-loop study

We analyze the critical behavior of isotropic systems with dipole-dipole interaction by renormalization-group methods in fixed space-time dimensions. Working in three-dimensional theory we analytically find three-loop expressions for critical exponents in the limit of dominating dipole-dipole forces. Resummation of the series obtained provides numerical values close to $O(3)$-theory predictions, justifying the applicability of such a simplified model to systems with strong dipole-dipole interaction.

cond-mat.stat-mech↗

arXiv2022

Bi- and tetracritical phase diagrams in three dimensions

The critical behavior of many physical systems involves two competing $n^{}_1-$ and $n^{}_2-$component order-parameters, ${\bf S}^{}_1$ and ${\bf S}^{}_2$, respectively, with $n=n^{}_1+n^{}_2$. Varying an external control parameter $g$, %(e.g. uniaxial stress or magnetic field), one encounters ordering of ${\bf S}^{}_1$ below a critical (second-order) line for $g<0$ and of ${\bf S}^{}_2$ below another critical line for $g>0$. These two ordered phases are separated by a first-order line, which meets the above critical lines at a bicritical point, or by an intermediate (mixed) phase, bounded by two critical lines, which meet the above critical lines at a tetracritical point. For $n=1+2=3$, the critical behavior around the (bi- or tetra-) multicritical point either belongs to the universality class of a non-rotationally invariant (cubic or biconical) fixed point, or it has a fluctuation driven first-order transition. These asymptotic behaviors arise only very close to the transitions. We present accurate renormalization-group flow trajectories yielding the effective crossover exponents near multicriticality.

cond-mat.stat-mech↗

arXiv2022

Different critical behaviors in cubic to trigonal and tetragonal perovskites

Perovskites like LaAlO3 (or SrTiO3) undergo displacive structural phase transitions from a cubic crystal to a trigonal (or tetragonal) structure. For many years, the critical exponents in both these types of transitions have been fitted to those of the isotropic three-components Heisenberg model. However, field theoretical calculations showed that the isotropic fixed point of the renormalization group is unstable, and renormalization group iterations flow either to a cubic fixed point or to a fluctuation-driven first-order transition. Here we show that these two scenarios correspond to the cubic to trigonal and to the cubic to tetragonal transitions, respectively. In both cases, the critical behavior is described by slowly varying effective critical exponents, which exhibit universal features. For the trigonal case, we predict a crossover of the effective exponents from their Ising values to their cubic values (which are close to the isotropic ones). For the tetragonal case, the effective exponents can have the isotropic values over a wide temperature range, before exhibiting large changes en route to the first-order transition. New renormalization group calculations near the isotropic fixed point in three dimensions are presented and used to estimate the effective exponents, and dedicated experiments to test these predictions are proposed. Similar predictions apply to cubic magnetic and ferroelectric systems.

cond-mat.stat-mech↗

arXiv2022

Model A of critical dynamics: 5-loop $\varepsilon$ expansion study

We have calculated the five-loop RG expansions of the $n$-component A model of critical dynamics in dimensions $d=4-\varepsilon$ within the Minimal Subtraction scheme. This is made possible by using the advanced diagram reduction method and the Sector Decomposition technique adapted to the problems of critical dynamics. The $\varepsilon$ expansions for the critical dynamic exponent $z$ for an arbitrary value of the order parameter dimension $n$ are derived. Based on these series, the numerical estimates of $z$ for different universality classes are extracted and compared with the results obtained within different theoretical and experimental methods.

cond-mat.stat-mech↗

arXiv2021

The dynamic critical exponent $z$ for 2d and 3d Ising models from five-loop $ε$ expansion

We calculate the dynamic critical exponent $z$ for 2d and 3d Ising universality classes by means of minimally subtracted five-loop $\varepsilon$ expansion obtained for the one-component model A. This breakthrough turns out to be possible through the successful adaptation of the Sector Decomposition technique to the problems of critical dynamics. The obtained fifth perturbative order accompanied by the use of advanced resummation techniques for asymptotic series allows us to find highly accurate numerical estimates of $z$: for two- and three-dimensional cases we obtain $\boldsymbol{2.14(2)}$ and $\boldsymbol{2.0235(8)}$ respectively. The numbers found are in good agreement with recent results obtained using different approaches.

cond-mat.stat-mech↗

arXiv2021

Dissipation and spontaneous emission in quantum electrodynamical density functional theory based on optimized effective potential: A proof of concept study

We generalize the optimized effective potential (OEP) formalism in the quantum electrodynamical density functional theory (QEDFT) to the case of continuous distribution of photon modes, and study its applicability to dissipative dynamics of electron systems interacting with photons of lossy cavities. Specifically, we test whether this technique is capable of capturing the quantum features of electron-photon interaction related to spontaneous emission and the corresponding energy transfer from the electrons to cavity photons. For this purpose, we analyze a discrete three-site system with one electron coupled to photons of the cavity, which, in fact, is a minimal model allowing to eliminate classical radiation and the corresponding energy loss, but still have nontrivial density dynamics. By considering two typical spectral densities of photon modes, modeling (i) lossy cavity with Lorentzian broadening of photon peaks, and (ii) the Ohmic bath, and several representative dynamical regimes, we find that OEP-QEDFT demonstrates a good qualitative and quantitative performance, especially in the case when the disspation is dominated by one-photon processes.

cond-mat.mes-hall↗