arXiv subjects

Evgueni V. Chulkov

Publications and source records attributed to Evgueni V. Chulkov.

At least 19 recordsLinked to original sources

arXiv2026

Epitaxial growth of beta-bismuthene on Sb2Te3

Over the past decades, two-dimensional crystals have attracted considerable interest as promising materials for electronic and optoelectronic applications. Among them, graphene analogs composed of heavy atoms occupy a particularly distinctive niche due to their enhanced spin-orbit interaction. Here, we present an epitaxial heterointerface formed by beta-bismuthene on Sb2Te3, a well-known three-dimensional topological insulator. Using scanning tunneling microscopy, we systematically investigated the effects of Bi coverage and substrate temperature on nucleation processes, island morphology, and atomic structure. In addition, substrate-induced defects were identified throughout the bismuthene lattice.

cond-mat.mtrl-sci↗

arXiv2026

Contrasting impurity-induced magnetism and dynamics in 2H-MoTe2

We investigate the behavior of interstitial $^8$Li$^+$ implanted near the surface of 2H-MoTe$_2$ using $β$-detected NMR. We find that, unlike the muon, $^8$Li$^+$ does not show any signature of induced magnetism. This result is consistent with density functional theory, which identifies the Li stopping site at the 2a Wyckoff position in the van der Waals gap and confirms the absence of detectable Li-induced electronic spin polarization. Both the spin-lattice relaxation and the resonance lines show evidence of strong spin dynamics above $\sim 200$ K, reminiscent of local stochastic $^8$Li$^+$ motion within a cage. The resonance line shape consists of quadrupolar satellites on top of a broad central peak. To better understand the interaction of $^8$Li$^+$ with the host material, we employ a frequency-comb measurement, by simultaneously exciting four frequencies corresponding to the first-order quadrupolar satellite transitions, $ν_0 \pm 3ν_{\mathrm{comb}}$ and $ν_0 \pmν_{\mathrm{comb}}$ around the Larmor frequency $ν_0$ as a function of $ν_{\mathrm{comb}}$. This offers an enhanced sensitivity to the quadrupolar split portion of the line. Using this method, we find a small decrease of the quadrupolar frequency with increasing temperature, showing the typical behavior associated with thermally excited phonons and the absence of any magnetic response which was observed with other defects in 2H-MoTe$_2$.

cond-mat.mtrl-sci↗

arXiv2025

Mastering the growth of antimonene on Bi2Se3: strategies and insights

Antimonene, the two-dimensional phase of antimony, appears in two distinct allotropes when epitaxially grown on Bi2Se3: the puckered asymmetric washboard (α) and buckled honeycomb (β) bilayer structures. As-deposited antimony films exhibit varying proportions of single α and β structures. We identify the conditions necessary for ordered, pure-phase growth of single to triple β-antimonene bilayers. Additionally, we determine their electronic structure, work function, and characteristic core-level binding energies, offering an explanation for the relatively large chemical shifts observed among the different phases. This study not only establishes a protocol for achieving a single β phase of antimonene but also provides key signatures for distinguishing between the different allotropes using standard spectroscopic and microscopic techniques.

cond-mat.mtrl-sci↗

arXiv2025

Prediction and observation of the first antiferromagnetic topological insulator

Magnetic topological insulators (MTIs) are narrow gap semiconductor materials that combine non-trivial band topology and magnetic order. Unlike their nonmagnetic counterparts, MTIs may have some of the surfaces gapped due to breaking the time-reversal symmetry, which enables a number of exotic phenomena having potential applications in spintronics. So far, MTIs have only been created by means of doping nonmagnetic TIs with 3d transition metal elements, however, such an approach leads to strongly inhomogeneous magnetic and electronic properties of these materials, restricting the observation of important effects to very low temperatures. Finding intrinsic MTI, i.e. a stoichiometric well-ordered magnetic compound, could be an ideal solution to these problems, but no such material was observed to date. Here, using density functional theory we predict and further confirm by means of structural, transport, magnetic, angle- and spin-resolved photoemission spectroscopy measurements the realization of the antiferromagnetic (AFM) TI phase, that is hosted by the van der Waals layered compound MnBi$_2$Te$_4$. An interlayer AFM ordering makes MnBi$_2$Te$_4$ invariant with respect to the combination of the time-reversal ($Θ$) and primitive-lattice translation ($T_{1/2}$) symmetries, $S = ΘT_{1/2}$, giving rise to the $Z_2$ topological classification of AFM insulators. We find $Z_2 = 1$ for MnBi$_2$Te$_4$, which confirms its topologically nontrivial nature. The $S$-breaking (0001) surface of MnBi$_2$Te$_4$ exhibits a giant bandgap in the topological surface state as evidenced by ab initio calculations and photoemission measurements. These results culminate almost a decade-long search of an AFMTI, predicted in 2010. Furthermore, MnBi$_2$Te$_4$ is the first intrinsic magnetic TI realized experimentally.

cond-mat.mtrl-sci↗

arXiv2023

On the floating of the topological surface state on top of a thick lead layer: The case of the Pb/Bi2Se3 interface

The puzzling question about the floating of the topological surface state on top of a thick Pb layer, has now possibly been answered. A study of the interface made by Pb on Bi2Se3 for different temperature and adsorbate coverage condition, allowed us to demonstrate that the evidence reported in the literature can be related to the surface diffusion phenomenon exhibited by the Pb atoms, which leaves the substrate partially uncovered. Comprehensive density functional theory calculations show that despite the specific arrangement of the atoms at the interface, the topological surface state cannot float on top of the adlayer but rather tends to move inward within the substrate.

cond-mat.mtrl-sci↗

arXiv2022

High Chern number van der Waals magnetic topological multilayers MnBi$_2$Te$_4$/hBN

Chern insulators are two-dimensional magnetic topological materials that conduct electricity along their edges via the one-dimensional chiral modes. The number of these modes is a topological invariant called the first Chern number $C$, that defines the quantized Hall conductance as $S_{xy}= C e^2/h$. Increasing $C$ is pivotal for the realization of low-power-consumption topological electronics, but there has been no clear-cut solution of this problem so far, with the majority of existing Chern insulators showing $C=1$. Here, by using state-of-the-art theoretical methods, we propose an efficient approach for the realization of the high-$C$ Chern insulator state in MnBi$_2$Te$_4$/hBN van der Waals multilayer heterostructures. We show that a stack of $n$ MnBi$_2$Te$_4$ films with $C=1$ intercalated by hBN monolayers gives rise to a high Chern number state with $C=n$, characterized by $n$ chiral edge modes. This state can be achieved both under the external magnetic field and without it, both cases leading to the quantized Hall conductance $S_{xy}= C e^2/h$. Our results therefore pave way to practical high-$C$ quantized Hall systems.

cond-mat.mes-hall↗

arXiv2022

Relaxation of photo-excited hot carriers beyond multi-temperature models: General theory description verified by experiments on Pb/Si(111)

The equilibration of electronic carriers in metals after excitation by an ultra-short laser pulse provides an important class of non-equilibrium phenomena in metals and allows measuring the effective electron-phonon coupling parameter. Since the observed decay of the electronic distribution is governed by the interplay of both electron-electron and electron-phonon scattering, the interpretation of experimental data must rely on models that ideally should be easy to handle, yet accurate. In this work, an extended rate-equation model is proposed that explicitly includes non-thermal electronic carriers while at the same time incorporating data from first-principles calculations of the electron-phonon coupling via Eliashberg-Migdal theory. The model is verified against experimental data for thin Pb films grown on Si(111). Improved agreement between theory and experiment at short times (<0.3ps) due to non-thermal electron contributions is found. Moreover, the rate equations allow for widely different coupling strength to different phonon subsystems. Consequently, an indirect, electron-mediated energy transfer between strongly and weakly coupled groups of phonons can be observed in the simulations that leads to a retarded equilibration of the subsystems only after several picoseconds.

cond-mat.mtrl-sci↗

arXiv2022

Hydrogen-impurity induced unconventional magnetism in semiconducting molybdenum ditelluride

Layered transition-metal dichalcogenides are proposed as building blocks for van der Waals (vdW) heterostructures due to their graphene-like two dimensional structure. For this purpose, a magnetic semiconductor could represent an invaluable component for various spintronics and topotronics devices. Here, we combine different local magnetic probe spectroscopies with angle-resolved photoemission and density-functional theory calculations to show that 2H-MoTe2 is on the verge of becoming magnetic. Our results present clear evidence that the magnetism can be "switched on" by a hydrogen-like impurity. We also show that this magnetic state survives up to the free surface region, demonstrating the material's potential applicability as a magnetic component for thin-film heterostructures.

cond-mat.mtrl-sci↗

arXiv2020

Domain wall induced spin-polarized flat bands in antiferromagnetic topological insulators

A flat band in fermionic system is a dispersionless single-particle state with a diverging effective mass and nearly zero group velocity. These flat bands are expected to support exotic properties in the ground state, which might be important for a wide range of promising physical phenomena. For many applications it is highly desirable to have such states in Dirac materials, but so far they have been reported only in non-magnetic Dirac systems. In this work we propose a realization of topologically protected spin-polarized flat bands generated by domain walls in planar magnetic topological insulators. Using first-principles material design we suggest a family of intrinsic antiferromagnetic topological insulators with an in-plane sublattice magnetization and a high Néel temperature. Such systems can host domain walls in a natural manner. For these materials, we demonstrate the existence of spin-polarized flat bands in the vicinity of the Fermi level and discuss their properties and potential applications.

cond-mat.mes-hall↗

arXiv2018

Possible Experimental Realization of a Basic Z2 Topological Semimetal

We report experimental and theoretical evidence that GaGeTe is a basic $Z_2$ topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the primer 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion in the \textit{T}-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron- and hole-like carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.

cond-mat.mtrl-sci↗

arXiv2018

Unique thickness-dependent properties of the van der Waals interlayer antiferromagnet $\mathrm{MnBi_2Te_4}$ films

Using density functional theory and Monte Carlo calculations, we study the thickness dependence of the magnetic and electronic properties of a van der Waals interlayer antiferromagnet in the two-dimensional limit. Considering $\mathrm{MnBi_2Te_4}$ as a model material, we find it to demonstrate a remarkable set of thickness-dependent magnetic and topological transitions. While a single septuple layer block of $\mathrm{MnBi_2Te_4}$ is a topologically trivial ferromagnet, the thicker films made of an odd (even) number of blocks are uncompensated (compensated) interlayer antiferromagnets, which show wide bandgap quantum anomalous Hall (zero plateau quantum anomalous Hall) states. Thus, $\mathrm{MnBi_2Te_4}$ is the first stoichiometric material predicted to realize the zero plateau quantum anomalous Hall state intrinsically. This state has been theoretically shown to host the exotic axion insulator phase.

cond-mat.mtrl-sci↗

arXiv2018

Highly-ordered wide bandgap materials for quantized anomalous Hall and magnetoelectric effects

An interplay of spin-orbit coupling and intrinsic magnetism is known to give rise to the quantum anomalous Hall and topological magnetoelectric effects under certain conditions. Their realization could open access to low power consumption electronics as well as many fundamental phenomena like image magnetic monopoles, Majorana fermions and others. Unfortunately, being realized very recently, these effects are only accessible at extremely low temperatures and the lack of appropriate materials that would enable the temperature increase is a most severe challenge. Here, we propose a novel material platform with unique combination of properties making it perfectly suitable for the realization of both effects at elevated temperatures. The key element of the computational material design is an extension of a topological insulator (TI) surface by a thin film of ferromagnetic insulator, which is both structurally and compositionally compatible with the TI. Following this proposal we suggest a variety of specific systems and discuss their numerous advantages, in particular wide band gaps with the Fermi level located in the gap.

cond-mat.mtrl-sci↗

arXiv2018

Probing topological insulators surface states via plasma-wave Terahertz detection

Topological insulators (TIs) represent a novel quantum state of matter, characterized by edge or surface-states, showing up on the topological character of the bulk wave functions. Allowing electrons to move along their surface, but not through their inside, they emerged as an intriguing material platform for the exploration of exotic physical phenomena, somehow resembling the graphene Dirac-cone physics, as well as for exciting applications in optoelectronics, spintronics, nanoscience, low-power electronics, and quantum computing. Investigation of topological surface states (TSS) is conventionally hindered by the fact that in most of experimental conditions the TSS properties are mixed up with those of bulk-states. Here, we devise a novel tool to unveil TSS and to probe related plasmonic effects. By engineering Bi2Te(3-x)Sex stoichiometry, and by gating the surface of nanoscale field-effect-transistors, exploiting thin flakes of Bi2Te2.2Se0.8 or Bi2Se3, we provide the first demonstration of room-temperature Terahertz (THz) detection mediated by over-damped plasma-wave oscillations on the "activated" TSS of a Bi2Te2.2Se0.8 flake. The reported detection performances allow a realistic exploitation of TSS for large-area, fast imaging, promising superb impacts on THz photonics.

cond-mat.mes-hall↗

arXiv2017

Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators

We combine low energy muon spin rotation (LE-$μ$SR) and soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and electronic properties of magnetically doped topological insulators, (Bi,Sb)$_2$Te$_3$. We find that one achieves a full magnetic volume fraction in samples of (V/Cr)$_x$(Bi,Sb)$_{2-x}$Te$_3$ at doping levels x $\gtrsim$ 0.16. The observed magnetic transition is not sharp in temperature indicating a gradual magnetic ordering. We find that the evolution of magnetic ordering is consistent with formation of ferromagnetic islands which increase in number and/or volume with decreasing temperature. Resonant ARPES at the V $L_3$ edge reveals a nondispersing impurity band close to the Fermi level as well as V weight integrated into the host band structure. Calculations within the coherent potential approximation of the V contribution to the spectral function confirm that this impurity band is caused by V in substitutional sites. The implications of our results on the observation of the quantum anomalous Hall effect at mK temperatures are discussed.

cond-mat.mtrl-sci↗

arXiv2017

Large-gap magnetic topological heterostructure formed by subsurface incorporation of a ferromagnetic layer

Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) for technological applications. While most studies have focused on doping magnetic impurities to open a gap at the surface-state Dirac point, many undesirable effects have been reported to appear in some cases that makes it difficult to determine whether the gap opening is due to the time-reversal symmetry breaking or not. Furthermore, the realization of the QAHE has been limited to low temperatures. Here we have succeeded in generating a massive Dirac cone in a MnBi2Se4 /Bi2Se3 heterostructure which was fabricated by self-assembling a MnBi2Se4 layer on top of the Bi2Se3 surface as a result of the co-deposition of Mn and Se. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the fabricated MnBi2Se4 /Bi2Se3 heterostructure shows ferromagnetism up to room temperature and a clear Dirac-cone gap opening of ~100 meV without any other significant changes in the rest of the band structure. It can be considered as a result of the direct interaction of the surface Dirac cone and the magnetic layer rather than a magnetic proximity effect. This spontaneously formed self-assembled heterostructure with a massive Dirac spectrum, characterized by a nontrivial Chern number C = -1, has a potential to realize the QAHE at significantly higher temperatures than reported up to now and can serve as a platform for developing future " topotronics" devices.

cond-mat.mtrl-sci↗

arXiv2015

Termination-dependent surface properties in the giant-Rashba semiconductors BiTeX (X = Cl, Br, I)

The non-centrosymmetric semiconductors BiTeX (X = Cl, Br, I) show large Rashba-type spin-orbit splittings in their electronic structure making them candidate materials for spin-based electronics. However, BiTeI(0001) single crystal surfaces usually consist of stacking-fault-induced domains of Te and I terminations implying a spatially inhomogeneous electronic structure. Here we combine scanning tunneling microscopy (STM), photoelectron spectroscopy (ARPES, XPS) and density functional theory (DFT) calculations to systematically investigate the structural and electronic properties of BiTeX(0001) surfaces. For X = Cl, Br we observe macroscopic single-terminated surfaces. We discuss chemical characteristics among the three materials in terms of bonding character, surface electronic structure, and surface morphology.

cond-mat.mtrl-sci↗

arXiv2014

The Density of Surface States in Weyl Semimetals

Weyl semimetal is a three-dimensional material with a conical spectrum near an even number of point nodes, where two bands touch each other. Here we study spectral properties of surface electron states in such a system. We show that the density of surface states possesses a logarithmic singularity for the energy $\varepsilon \to 0$. It decreases linearly at the intermediate energy of surface electron states and approaches zero as $\sqrt{1-\varepsilon}$ for $\varepsilon \to 1$. This universal behavior is a hallmark of the topological order that offers a new wide range of applications.

cond-mat.mes-hall↗

arXiv2013

Nonlocal Edge State Transport in Topological Insulators

We use the N-terminal scheme for studying the edge state transportin in two-dimensional topological insulators. We find the universal nonlocal response in the ballistic transport approach. This macroscopic exhibition of the topological order offers different areas for applications.

cond-mat.mes-hall↗