arXiv subjects

E. E. Krasovskii

Publications and source records attributed to E. E. Krasovskii.

At least 19 recordsLinked to original sources

arXiv2026

Green's function theory of magnetism in Bi$_2$CuO$_4$: anisotropic Heisenberg XYZ model

The Green's function theory of Lymar' and Rudoi [Theor. Math. Phys. vol. 21, 990 (1974)] is generalized to the case of multiple intra- and inter-sublattice magnetic interactions in a collinear spin-half antiferromagnet and applied to magnetic excitations in Bi$_2$CuO$_4$. The spin Hamiltonian includes both the out-of-plane and in-plane symmetric anisotropy terms and the Zeeman term, which describes the interaction with an external magnetic field $B$ applied along the Néel vector. Within the spin-wave approximation we calculate spin excitation dispersion, antiferromagnetic resonance frequencies and the critical field $B_c$ of the spin-flop metamagnetic transition. A weak in-plane anisotropy is shown to result in a gap in the acoustic-like branch of the excitations. The gap nonlinearly depends on the external field and closes at $B=B_c$. An expression for the Neel temperature in the Tyablikov random phase approximation at zero field is derived. For the parameters derived from the recent inelastic neutron scattering study by Yuan et al. [Phys. Rev. B vol. 103, 134436 (2021)] it gives $T_{\rm N}\approx 52$~K.

cond-mat.mtrl-sci↗

arXiv2026

Plasmon manipulation by exchange magnetic field in two-dimensional spin-orbit coupled electronic systems: A higher-order relativistic k.p study

A higher-order relativistic k.p model is developed to describe plasmon excitations in two-dimensional (2D) electronic systems with spin-orbit coupling (SOC) and magnetic-exchange interactions. Derived entirely from ab initio band structure, the model allows for a non-Rashba spin-momentum locking and enables a direct coupling of the exchange field to the real spin of electrons. Using the BiTeI trilayer (hexagonal C3v symmetry) and the Si-terminated surface state of TbRh2Si2 (cubic C4v symmetry) as prototypes, we show that the exchange field induces strong, symmetry-dependent modifications of the band structure and plasmon dispersion. In BiTeI, it breaks the sixfold symmetry and leads to anisotropic, nonreciprocal plasmon modes, while in TbRh2Si2 it suppresses the characteristic triple spin winding and alters the plasmon damping. The results reveal that the interplay between SOC and exchange magnetism enables magnetic control of collective charge excitations in 2D spin-orbit systems beyond the Rashba paradigm.

cond-mat.other↗

arXiv2025

Unoccupied bands in the molybdenum dichalcogenides MoS$_2$, MoSe$_2$, and MoTe$_2$

We present angle-resolved reflected electron spectroscopy (ARRES) data for the three molybdenum-based transition metal dichalcogenides (TMDs) \mos, \mose, and \mote. To follow the changes as the series moves from S to Se to Te in more detail, we determine accurate IV-spectra for monolayers and bulk TMDs. These experimental data sets are then compared with theoretical predictions for both the unoccupied band structure and the scattering density of states. We find good agreement, especially for lower energies where inelastic effects are relatively unimportant. Furthermore, we identify a series of interlayer resonances for which the dependence of the hybridization effects on the layer count is observed. Although these resonances bear similarity to interlayer resonances in hBN and graphene, they differ in their character, being dominated by unoccupied $d$-states of the chalcogen-atoms. The unoccupied states studied and analyzed here play a key role in all processes that require an electron to temporarily reside in a state above the vacuum level, such as in photoemission and secondary electron emission experiments.

cond-mat.mes-hall↗

arXiv2025

Topological properties of a chain of interacting electrons

Within the framework of a one-dimensional model of interacting electrons, the ground state of an electron liquid is studied. Using the exact solution of the model, the ground state phase diagram and zero-energy Majorana edge functions in a finite chain are calculated. The winding number invariant reflects the topological nature of the electron liquid. The phase diagram includes two topological phases with different winding number invariants, the topologically trivial Mott insulator phase, and three critical phase transition points. Numerical calculations confirm and illustrate the analytical results.

cond-mat.str-el↗

arXiv2024

Fano physics behind the N-resonance in graphene

Bound states and scattering resonances in the unoccupied continuum of a two-dimensional crystal predicted in [Phys$.$Rev$.$ B 87, 041405(R) (2013)] are considered within an exactly solvable model. A close connection of the observed resonances with those arising in the Fano theory is revealed. The resonance occurs when the lateral scattering couples the layer-perpendicular incident electron wave to a strictly bound state. The coupling strength determines the location of the pole in the scattering amplitude in the complex energy plane, which is analytically shown to lead to a characteristic Fano-lineshape of the energy dependence of the electron transmissivity through the crystal. The implications for the timing of the resonance scattering are discussed. The analytical results are illustrated by ab initio calculations for a graphene monolayer.

cond-mat.mes-hall↗

arXiv2024

Theory of circular dichroism in angle- and spin-resolved photoemission from the surface state on Bi(111)

Circular dichroism (CD) of photoemission from a surface state on Bi(111) is considered within an {\it ab initio} one-step theory of photoemission. The symmetry of the azimuthal distribution of CD for different spin directions is discussed in terms of the spin structure of the initial states. Both normal and off-normal light incidence are considered. Strong photon energy dependence of photoemission in the ultraviolet range is observed. The principal difference between the initial state spin polarization and the spin photocurrent is emphasized and problems with revealing the orbital angular moment with photoemission are pointed to.

cond-mat.mtrl-sci↗

arXiv2024

Negative transit time in non-tunneling electron transmission through graphene multilayers

Attosecond dynamics of electron transmission through atomically-thin crystalline films is studied with an {\em ab initio} scattering theory. The temporal character of the electron propagation through graphene multilayers is traced to the band structure of bulk graphite: In the forbidden gaps the wave packet transit time $τ_\mathrm{T}$ saturates with thickness and in the allowed bands $τ_\mathrm{T}$ oscillates following transmission resonances. Hitherto unknown negative transit time due to in-plane scattering is discovered in monolayers of graphene, h-BN, and oxygen. Moreover, Wigner time delay is found to diverge at the scattering resonances caused by the emergence of secondary diffracted beams. This offers a way to manipulate the propagation timing of the wave packet without sacrificing the transmitted intensity. The spatial reshaping of the wave packet at the resonances may help elucidate details of the streaking by an inhomogeneous field at the surface.

cond-mat.mtrl-sci↗

arXiv2024

Attosecond dynamics of electron scattering by an absorbing layer

Attosecond dynamics of electron reflection from a thin film is studied based on a one-dimensional jellium model. Following the Eisenbud-Wigner-Smith concept, the reflection time delay $Δτ_{\rm R}$ is calculated as the energy derivative of the phase of the complex reflection amplitude $r$. For a purely elastic scattering by a jellium slab of a finite thickness $d$ the transmission probability $T$ oscillates with the momentum $K$ in the solid with a period $π/d$, and $Δτ_{\rm R}$ closely follows these oscillations. The reflection delay averaged over an energy interval grows with $d$, but in the limit of $d\to\infty$ the amplitude $r$ becomes real, so $Δτ_{\rm R}$ vanishes. This picture changes substantially with the inclusion of an absorbing potential $-iV_{\rm i}$: As expected, for a sufficiently thick slab the reflection amplitude now tends to its asymptotic value for a semi-infinite crystal. Interestingly, for $V_{\rm i} \ne 0$, around the $T(E)$ maxima, the $Δτ_{\rm R}(E)$ curve strongly deviates from $T(E)$, showing a narrow dip just at the $Δτ_{\rm R}(E)$ maximum for $V_{\rm i}=0$. An analytical theory of this counterintuitive behavior is developed.

cond-mat.mtrl-sci↗

arXiv2021

Spatial aspects of spin polarization of structurally split surface states in thin films with magnetic exchange and spin-orbit interaction

A theoretical study is presented of the effect of an in-plane magnetic exchange field on the band structure of centrosymmetric films of noble metals and topological insulators. Based on an ab initio relativistic $\mathbf{k}\cdot\mathbf{p}$ theory, a minimal effective model is developed that describes two coupled copies of a Rashba or Dirac electronic system residing at the opposite surfaces of the film. The coupling leads to a structural gap at $\barΓ$ and causes an exotic redistribution of the spin density in the film when the exchange field is introduced. We apply the model to a nineteen-layer Au(111) film and to a five-quintuple-layer Sb$_2$Te$_3$ film. We demonstrate that at each film surface the exchange field induces spectrum distortions similar to those known for Rashba or Dirac surface states with an important difference due to the coupling: At some energies, one branch of the state loses its counterpart with the oppositely directed group velocity. This suggests that a large-angle electron scattering between the film surfaces through the interior of the film is dominant or even the only possible for such energies. The spin-density redistribution accompanying the loss of the counterpart favors this scattering channel.

cond-mat.mtrl-sci↗

arXiv2021

Comment on "Distinction of Electron Dispersion in Time-Resolved Photoemission Spectroscopy"

In a recent paper [Phys. Rev. Lett. 125, 043201 (2020)] (Ref.1) Liao et al. propose a theory of the interferometric photoemission delay based on the concepts of the photoelectron phase and photoelectron effective mass. The present comment discusses the applicability and limitations of the proposed approach based on an ab initio analysis supported by vast literature. Two central assumptions of the paper are questioned, namely that the photoelectron can be characterized by a phase (have a well-defined phase velocity), and that it can always be ascribed an effective mass Theories based on these concepts are concluded to be inapplicable to real solids, which is illustrated by the example of the system addressed in Ref. 1. That the basic assumptions of the theory are never fulfilled in nature discredits the underlying idea of the "time-domain interferometric solid-state energy-momentum-dispersion imaging method" suggested in Ref. 1. Apart from providing a necessary caution to experimentalists, the present comment also gives an insight into the photoelectron wave function and points out problems and pitfalls inherent in modeling real crystals.

cond-mat.mtrl-sci↗

arXiv2020

Variety of scenarios of the magnetic exchange response in topological insulators

We present an ab initio relativistic k.p theory of the effect of magnetic exchange field on the band structure in the gap region of bulk crystals and thin films of three-dimensional layered topological insulators. For the field perpendicular to the layers (along $z$), we reveal novel unconventional scenarios of the response of the band-gap edges to the magnetization. The modification of the valence and conduction states is considered in terms of their $Γ$-point spin $s^z$ and total angular momentum $J^z$ on the atomic sites where the states are localized. The actual scenario depends on whether $s^z$ and $J^z$ have the same or opposite sign. In particular, the opposite sign for the valence state and the same sign for the conduction state give rise to an unconventional response in Bi$_2$Te$_3$ -- both in the bulk crystal and in ultra-thin films, which fundamentally distinguishes this topological insulator from Bi$_2$Se$_3$, where both states have the same sign. To gain a deeper insight into different scenarios in insulators with both inverted and non-inverted zero-field band structure, a minimal four-band third-order k.p model is constructed from first principles. Within this model, we analyze the field-induced band structure of the insulators and identify Weyl nodes that appear in a magnetic phase and behave differently depending on the scenario. We characterize the topology of the modified band structure by the Chern number $\mathcal{C}$ and find the unconventional response to be accompanied by a large Chern number $\mathcal{C}=\pm3$.

cond-mat.mes-hall↗

arXiv2020

Ab initio k.p theory of spin-momentum locking: Application to topological surface states

Based on ab initio relativistic ${\mathbf k}\cdot{\mathbf p}$ theory, we derive an effective two-band model for surface states of three-dimensional topological insulators up to seventh order in $\mathbf{k}$. It provides a comprehensive description of the surface spin structure characterized by a non-orthogonality between momentum and spin. We show that the oscillation of the non-orthogonality with the polar angle of $\mathbf{k}$ with a $π/3$ periodicity can be seen as due to effective six-fold symmetric spin-orbit magnetic fields with a quintuple and septuple winding of the field vectors per single rotation of $\mathbf{k}$. Owing to the dominant effect of the classical Rashba field, there remains a single-winding helical spin structure but with a periodic few-degree deviation from the orthogonal locking between momentum and spin.

cond-mat.mes-hall↗

arXiv2020

Observation of a cubic Rashba effect in the surface spin structure of rare-earth ternary materials

Spin-orbit interaction and structure inversion asymmetry in combination with magnetic ordering is a promising route to novel materials with highly mobile spin-polarized carriers at the surface. Spin-resolved measurements of the photoemission current from the Si-terminated surface of the antiferromagnet TbRh2Si2 and their analysis within an ab initio one-step theory unveil an unusual triple winding of the electron spin along the fourfold-symmetric constant energy contours of the surface states. A two-band k.p model is presented that yields the triple winding as a cubic Rashba effect. The curious in-plane spin-momentum locking is remarkably robust and remains intact across a paramagnetic-antiferromagnetic transition in spite of spin-orbit interaction on Rh atoms being considerably weaker than the out-of-plane exchange field due to the Tb 4f moments.

cond-mat.mes-hall↗

arXiv2019

Non-universal Transverse Electron Mean Free Path through Few-layer Graphene

In contrast to the in-plane transport electron mean-free path in graphene, the transverse mean-free path has received little attention and is often assumed to follow the 'universal' mean-free path (MFP) curve broadly adopted in surface and interface science. Here we directly measure transverse electron scattering through graphene from 0 to 25 eV above the vacuum level both in reflection using Low Energy Electron Microscopy and in transmission using electron-Volt Transmission Electron Microscopy. From this data, we obtain quantitative MFPs for both elastic and inelastic scattering. Even at the lowest energies, the total MFP is just a few graphene layers and the elastic MFP oscillates with graphene layer number, both refuting the 'universal' curve. A full theoretical calculation taking the graphene band structure into consideration agrees well with experiment, while the key experimental results are reproduced even by a simple optical toy model.

cond-mat.mtrl-sci↗

arXiv2019

An all-electron product-basis set: application to plasmon anisotropy in simple metals

An efficient basis set for products of all-electron wave functions is proposed, which comprises plane waves defined over the entire unit cell and orbitals confined to small non-overlapping spheres. The size of the set and the basis functions are, in principle, independent of the computational parameters of the band structure method. The approach is implemented in the extended LAPW method, and its properties and accuracy are discussed. The method is applied to analyze the dielectric response of the simple metals Al, Na, Li, K, Rb, and Cs with a focus on the origin of the anisotropy of the plasmon dispersion in Al and Na. The anisotropy is traced to tiny structures of the one-particle excitation spectra of Al and Na, and relevant experimental observations are explained.

cond-mat.mtrl-sci↗

arXiv2018

Stacking domains in graphene on silicon carbide: a pathway for intercalation

Graphene on silicon carbide (SiC) bears great potential for future graphene electronic applications because it is available on the wafer-scale and its properties can be custom-tailored by inserting various atoms into the graphene/SiC interface. It remains unclear, however, how atoms can cross the impermeable graphene layer during this widely used intercalation process. Here we demonstrate that, in contrast to the current consensus, graphene layers on SiC are not homogeneous, but instead composed of domains of different crystallographic stacking. We show that these domains are intrinsically formed during growth and that dislocations between domains dominate the (de)intercalation dynamics. Tailoring these dislocation networks, e.g. through substrate engineering, will increase the control over the intercalation process and could open a playground for topological and correlated electron phenomena in two-dimensional superstructures.

cond-mat.mtrl-sci↗

arXiv2017

Spin Filtering via Resonant Reflection of Relativistic Surface States

A microscopic approach is developed to scattering of surface states from a non-magnetic linear defect at a surface with strong spin-orbit interaction. Spin-selective reflection resonances in scattering of Rashba-split surface states by an atomic stripe are theoretically discovered in a proof-of-principle calculation for a model crystal potential. Spin-filtering properties of such linear defects are analyzed within an envelope-function formalism for a perturbed surface based on the Rashba Hamiltonian. The continuous Rashba model is found to be in full accord with the microscopic theory, which reveals the essential physics behind the scattering resonance. The spin-dependent reflection suggests a novel mechanism to manipulate spins on the nanoscale.

cond-mat.mes-hall↗

arXiv2017

Synchrotron radiation induced magnetization in magnetically-doped and pristine topological insulators

Quantum mechanics postulates that any measurement influences the state of the investigated system. Here, by means of angle-, spin-, and time-resolved photoemission experiments and ab initio calculations we demonstrate how non-equal depopulation of the Dirac cone (DC) states with opposite momenta in V-doped and pristine topological insulators (TIs) created by a photoexcitation by linearly polarized synchrotron radiation (SR) is followed by the hole-generated uncompensated spin accumulation and the SR-induced magnetization via the spin-torque effect. We show that the photoexcitation of the DC is asymmetric, that it varies with the photon energy, and that it practically does not change during the relaxation. We find a relation between the photoexcitation asymmetry, the generated spin accumulation and the induced spin polarization of the DC and V 3d states. Experimentally the SR-generated in-plane and out-of-plane magnetization is confirmed by the $k_{\parallel}$-shift of the DC position and by the splitting of the states at the Dirac point even above the Curie temperature. Theoretical predictions and estimations of the measurable physical quantities substantiate the experimental results.

cond-mat.mtrl-sci↗