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A. V. Tarasov

Publications and source records attributed to A. V. Tarasov.

At least 19 recordsLinked to original sources
arXiv2025

Topological phase control in Mn1-xGexBi2Te4 via spin-orbit coupling and magnetic configuration engineering

Magnetic topological systems based on MnBi2Te4 have recently attracted significant attention due to their rich interplay between magnetism and topological electronic states. In this work, using density functional theory (DFT), we investigate topological phase transitions (TPTs) in Mn1-xGexBi2Te4 compounds with both ferromagnetic (FM) and antiferromagnetic (AFM) ordering under variations of spin-orbit coupling (SOC) strength and uniaxial strain along the c axis. We show that the emergence of a Weyl semimetal (WSM) phase requires the crossing of bands with opposite sz spin projections along the ΓZ direction. Modulation of SOC and strain can annihilate Weyl points via spin-selective hybridization, driving transitions into trivial or topological insulating phases. Furthermore, we demonstrate that local asymmetry in Mn/Ge substitution, particularly at 37.5% Ge concentration (Mn0.625Ge0.375Bi2Te4) can locally disrupt AFM interlayer coupling and induce a WSM state even in globally AFM systems, without external remagnetization. To optimize Weyl point separation and enhance the anomalous Hall effect (AHE), we propose partial substitution of Mn by Fe and Te by Se.

cond-mat.mtrl-sci↗
arXiv2024

Probing the Interaction Between Topological and Rashba-like Surface States in MnBi$_2$Te$_4$ Through Sn Doping

The presence of Rashba-like surface states (RSS) in the electronic structure of topological insulators (TIs) has been a longstanding topic of interest due to their significant impact on electronic and spin structures. In this study, we investigate the interaction between topological and Rashba-like surface states (TSS and RSS) in Mn$_{1-x}$Sn$_x$Bi$_2$Te$_4$ systems using density functional theory (DFT) calculations and high-resolution ARPES. Our findings reveal that increasing Sn concentration shifts RSS downward in energy, enhancing their influence on the electronic structure near the Fermi level. ARPES validates these predictions, capturing the evolution of RSS and their hybridization with TSS. Orbital analysis shows RSS are localized within the first three Te-Bi-Te trilayers, dominated by Bi $p$-orbitals, with evidence of the orbital Rashba effect enhancing spin-momentum locking. At higher Sn concentrations, RSS penetrate deeper into the crystal, driven by Sn $p$-orbital contributions. These results position Mn$_{1-x}$Sn$_x$Bi$_2$Te$_4$ as a tunable platform for tailoring electronic properties in spintronic and quantum technologies.

cond-mat.mtrl-sci↗
arXiv2024

Spin texture tunability in Mn$_{1-x}$Ge$_x$Bi$_2$Te$_4$ through varying Ge Concentration

The spin-resolved dispersion dependencies for the topological insulator Mn$_{1-x}$Ge$_x$Bi$_2$Te$_4$ in the $\bar{\rm K}\barΓ\bar{\rm K}'$ path of the Brillouin zone were studied by spin- and angle-resolved photoemission spectroscopy using laser radiation (Laser Spin-ARPES) with variation of the concentration of substitutional Ge atoms (x from 0.1 to 0.8) for in-plane ($s_x$) and out-of-plane ($s_z$) spin orientation. The formation of Rashba-like states is shown, which shift to lower energies with increasing Ge concentration. In the region of Ge concentrations from 50% to 75%, the contribution of these states to the formed spin-dependent dispersions becomes predominant. A pronounced in-plane ($s_y$) spin polarization, asymmetric for opposite $\pm k_\parallel$ directions, is revealed for the Dirac cone states, while the Rashba-like states exhibit a pronounced asymmetry in both in-plane ($s_y$) and out-of-plane ($s_z$) spin polarizations. Theoretical calculations confirmed the asymmetric polarization of the Rashba-like states formed in the $\bar{\rm K}\barΓ\bar{\rm K}'$ path of the BZ, simultaneously for in-plane and out-of-plane spin orientation. Constant energy maps for Rashba-like states show a pronounced $s_z$ spin component along the $\barΓ\bar{\rm K}$ direction, with a sign change as the contour crosses the $\barΓ\bar{\rm M}$ direction. The observed spin polarization can influence the development of spin devices based on magnetic topological insulators.

cond-mat.mes-hall↗
arXiv2024

Phase transitions, Dirac and WSM states in $\mathrm{Mn}_{1-x} \mathrm{Ge}_x \mathrm{Bi}_2 \mathrm{Te}_4$

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), an experimental and theoretical study of changes in the electronic structure (dispersion dependencies) and corresponding modification of the energy band gap at the Dirac point (DP) for topological insulator (TI) $\mathrm{Mn}_{1-x} \mathrm{Ge}_x \mathrm{Bi}_2 \mathrm{Te}_4$ have been carried out with gradual replacement of magnetic Mn atoms by non-magnetic Ge atoms when concentration of the latter was varied from 10$\%$ to 75$\%$. It was shown that when Ge concentration increases then the bulk band gap decreases and reaches zero plateau in the concentration range of 45$\%$-60$\%$ while non-topological surface states (TSS) are present and exhibit an energy splitting of 100 and 70 meV in different types of measurements. It was also shown that TSS disappear from the measured band dispersions at a Ge concentration of about 40$\%$. DFT calculations of $\mathrm{Mn}_{1-x} \mathrm{Ge}_x \mathrm{Bi}_2 \mathrm{Te}_4$ band structure were carried out to identify the nature of observed band dispersion features and to analyze a possibility of magnetic Weyl semimetal state formation in this system. These calculations were performed for both antiferromagnetic (AFM) and ferromagnetic (FM) ordering types while the spin-orbit coupling (SOC) strength was varied or a strain (compression or tension) along the $c$-axis was applied. Calculations show that two different series of topological phase transitions (TPTs) may be implemented in this system depending on the magnetic ordering. At AFM ordering transition between TI and trivial insulator phase goes through the Dirac semimetal state, whereas for FM phase such route admits three intermediate states instead of one (TI - Dirac semimetal - Weyl semimetal - Dirac semimetal - trivial insulator).

cond-mat.mtrl-sci↗
arXiv2023

Insight into the electronic structure of the centrosymmetric skyrmion magnet GdRu$_2$Si$_2$

The discovery of a square magnetic-skyrmion lattice in GdRu$_2$Si$_2$, with the smallest so far found skyrmion diameter and without a geometrically frustrated lattice, has attracted significant attention, particularly for potential applications in memory devices and quantum computing. In this work, we present a comprehensive study of surface and bulk electronic structures of GdRu$_2$Si$_2$ by utilizing momentum-resolved photoemission (ARPES) measurements and first-principles calculations. We show how the electronic structure evolves during the antiferromagnetic transition when a peculiar helical order of 4$f$ magnetic moments within the Gd layers sets in. A nice agreement of the ARPES-derived electronic structure with the calculated one has allowed us to characterize the features of the Fermi surface (FS), unveil the nested region along the $k_z$ at the corner of the 3D FS, and reveal their orbital compositions. Our findings suggest that the Ruderman-Kittel-Kasuya-Yosida interaction plays a decisive role in stabilizing the spiral-like order of Gd 4$f$ moments responsible for the skyrmion physics in GdRu$_2$Si$_2$. Our results provide a deeper understanding of electronic and magnetic properties of this material, which is crucial for predicting and developing novel skyrmion-based devices.

cond-mat.mtrl-sci↗
arXiv2022

Factors influencing the energy gap in topological states of antiferromagnetic MnBi$_2$Te$_4$

The experimentally measured angle-resolved photoemission dispersion maps for MnBi$_{2}$Te$_{4}$ samples, which show different energy gaps at the Dirac point (DP), are compared with the results of theoretical calculations to find the conditions for the best agreement between theory and experiment. We have analyzed different factors which influence the Dirac gap width: (i) the surface van der Waals (SvdW) distance between the first and second septuple layers (SLs), (ii) the magnetic moment on Mn atoms, (iii) the spin-orbit coupling (SOC) strength for the surface Te and Bi atoms and related changes in the localization of the topological surface states (TSSs). It was shown that all these factors may change the gap width at the DP in a wide range from 5 to $\sim$90~meV. We show that the Dirac gap variation is mainly determined by the corresponding changes in the TSSs spatial distribution. The best agreement between the presented experimental data (with the Dirac gaps between $\sim$15 and 55~meV) and the calculations takes place for a slightly compressed SvdW interval (of about -3.5~\% compared to the bulk value) with modified SOC for surface atoms (that can occur in the presence of various defects in the near-surface region). We show that upon changing the values of the SvdW interval and surface SOC strength the TSSs spatial distribution shifts between the SLs with opposite magnetizations, which leads to a non-monotonic change in the Dirac gap size.

cond-mat.mes-hall↗
arXiv2014

A Quasiclassical Approximation in the Theory of the Landau-Pomeranchuk Effect

Using the improved value of the screening angular parameter in the quasiclassical approximation of the Moliere multiple scattering theory we show that the best agreement between the Migdal theory of the LPM-effect and experiment is achieved if the multiple scattering of electrons by target atoms is described using the quasiclassical approximation instead of the traditionally used Born one.

hep-ph↗
arXiv2009

Formation of $πμ$ atoms in $K_{μ4} decay

We derive the decay rate of $πμ$ atom formation in $K_{μ4}$ decay. Using the obtained expressions we calculate the decay rate of atom formation and point out that considered decay can give a noticeable contribution as a background to the fundamental decay $K^+\to π^+ν\barν$.

hep-ph↗
arXiv2009

Final state interaction in kaons decays

The kaons decays to the pairs of charged and neutral pions are considered in the framework of the non-relativistic quantum mechanics. The general expressions for the decay amplitudes to the two different channels accounting for the strong interaction between pions are obtained. The developed approach allows one to estimate the contribution of terms of any order in strong interaction and correctly takes into account the electromagnetic interaction between the pions in the final state.

hep-ph↗
arXiv2008

Quantum-mechanical description of in-medium fragmentation

We present a quantum-mechanical description of quark-hadron fragmentation in a nuclear environment. It employs the path-integral formulation of quantum mechanics, which takes care of all phases and interferences, and which contains all relevant time scales, like production, coherence, formation, etc. The cross section includes the probability of pre-hadron (colorless dipole) production both inside and outside the medium. Moreover, it also includes inside-outside production, which is a typical quantum-mechanical interference effect (like twin-slit electron propagation). We observe a substantial suppression caused by the medium, even if the pre-hadron is produced outside the medium and no energy loss is involved. This important source of suppression is missed in the usual energy-loss scenario interpreting the effect of jet quenching observed in heavy ion collisions. This may be one of the reasons of a too large gluon density, reported by such analyzes.

hep-ph↗
arXiv2008

The electromagnetic effects in $K_{e4}$ decay

The final state interaction of pions in $K_{e4}$ decay allows one to obtain the value of the isospin and angular momentum zero $ππ$ scattering length $a_0^0$.We take into account the electromagnetic interaction of pions and isospin symmetry breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering length extraction from $K_{e4}$ decay.

hep-ph↗
arXiv2008

The isospin symmetry breaking effects in $K_{e4}$ decays

The Fermi-Watson theorem is generalized to the case of two coupled channels with different masses and applied to final state interaction in $K_{e4}$ decays. The impact of considered effect on the phase of the $ππ$ scattering is estimated and shown that it can be crucial for scattering lengths extraction from experimental data on $K_{e4}$ decays.

hep-ph↗
arXiv2007

Perturbative fragmentation

The Berger model of perturbative fragmentation of quarks to pions is improved by providing an absolute normalization and keeping all terms in a (1-z) expansion, which makes the calculation valid at all values of fractional pion momentum z. We also replace the nonrelativistic wave function of a loosely bound pion by the more realistic procedure of projecting to the light-cone pion wave function, which in turn is taken from well known models. The full calculation does not confirm the (1-z)^2 behavior of the fragmentation function (FF) predicted in for $z>0.5$, and only works at very large z>0.95, where it is in reasonable agreement with phenomenological FFs. Otherwise, we observe quite a different z-dependence which grossly underestimates data at smaller z. The disagreement is reduced after the addition of pions from decays of light vector mesons, but still remains considerable. The process dependent higher twist terms are also calculated exactly and found to be important at large z and/or pT.

hep-ph↗
arXiv2007

Diffractive Excitation of Heavy Flavors: Leading Twist Mechanisms

Diffractive production of heavy flavors is calculated within the light-cone dipole approach. Novel leading twist mechanisms are proposed, which involve both short and long transverse distances inside the incoming hadron. Nevertheless, the diffractive cross section turns out to be sensitive to the primordial transverse momenta of projectile gluons, rather than to the hadronic size. Our calculations agree with the available data for diffractive production of charm and beauty, and with the observed weak variation of the diffraction-to-inclusive cross section ratios as function of the hard scale.

hep-ph↗
arXiv2007

Electromagnetic effects and scattering lengths extraction from experimental data on $K \to 3π$ decays

The final state interactions in $K^\pm\toπ^\pmπ^0π^0$ decays are considered using the methods of non-relativistic quantum mechanics. We show how to take into account the largest electromagnetic effects in the analysis of experimental data, using the amplitudes calculated earlier. We propose the relevant expressions for amplitude corrections valid both above and below the two charged pion production threshold $M_{π^0π^0}=2m_{π^\pm}$, including the average effect for the threshold bin. These formulae can be used in the procedure of pion scattering lengths measurement from $M_{π^0π^0}$ spectrum.

hep-ph↗
arXiv2007

Electromagnetic corrections to final state interactions in $K\to 3π$ decays

The final state interactions of pions in decays $K^\pm\toπ^\pmπ^0π^0$ are considered using the methods of quantum mechanics. We show how to incorporate the electromagnetic effects in the amplitudes of these decays and to work out the relevant expressions valid above and below the two charged pions production threshold $M_c=2m$. The electromagnetic corrections are given as evaluated in a potential model.

hep-ph↗
arXiv2006

Dipole description of inclusive particle production

The effects of multiple interactions in colliding particles (e.g. in nucleus-nucleus collisions) are modeled using the light-cone dipole approach. Guided by the abelian analogue of multi-photon interactions in the production of a pair of charged particles, we relate the inclusive cross section of quark pair production with the cross sections of interaction of a QCD dipole with either the beam or the target.

hep-ph↗