Intercalation of graphene with transition and noble metals offers a versatile route to tailor its electronic and magnetic properties. Here, we investigate the structural and magnetic characteristics of the graphene/Au--Co/Co(0001)/W(110) system after Au intercalation, employing scanning tunneling microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), and scanning electron microscopy (SEM). We demonstrate the formation of a two-dimensional Au--Co surface alloy beneath graphene, characterized by a periodic network of triangular loop dislocations. The size and spacing of these dislocations exhibit an inverse correlation with the local Au concentration, which simultaneously drives nanoscale surface corrugation as a mechanism for relaxation of compressive stress. Despite pronounced topographic modulation, STM and STS reveal that the proximity-induced ferrimagnetic ordering in graphene remains robust across corrugated regions. Tip-induced mechanical deformation is shown to locally suppress this magnetic order by reducing the graphene--alloy separation and weakening the exchange coupling. These findings establish a direct link between intercalant concentration, structural relaxation, and spin--orbit and magnetic proximity effects, providing a pathway for spatially controlled engineering of graphene-based spintronic devices.​

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) $$\textrm{Mn}_{1-x} \textrm{Ge}_x \textrm{Bi}_2 \textrm{Te}_4$$ 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, the bulk band gap decreases and reaches zero plateau in the concentration range of 45–60% while trivial surface states (TrSS) 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 $$\textrm{Mn}_{1-x} \textrm{Ge}_x \textrm{Bi}_2 \textrm{Te}_4$$ band structure were carried out to identify the nature of observed band dispersion features and to analyze the 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. In the case of AFM ordering, the transition between TI and the trivial insulator phase passes 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). Weyl points that form in the FM system along the $$\varGamma \!Z$$ direction annihilate when either the SOC strength decreases or a sufficient tensile strain is applied, which is accompanied by the corresponding TPTs. Model calculations of the influence of local magnetic ordering in AFM $$\textrm{Mn}_{1-x} \textrm{Ge}_x \textrm{Bi}_2 \textrm{Te}_4$$ were carried out by alternating Mn layers with Ge-doped layers and showed that the magnetic Weyl semimetal state in this system is reachable at a Ge concentration of approximately 40% without application of any external magnetic fields.

Using angle-resolved photoemission spectroscopy (ARPES) with spin resolution, scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT) methods, we study the electronic structure of graphene-covered and bare Au/Co(0001) systems and reveal intriguing features, arising from the ferrimagnetic order in graphene and the underlying gold monolayer. In particular, a spin-polarized Dirac-cone-like state, intrinsically related to the induced magnetization of Au, was discovered at point. We have obtained a good agreement between experiment and theory for bare and graphene-covered Au/Co(0001) and have proven that both Au ferrimagnetism and the Dirac-cone-like band are intimately linked to the triangular loop dislocations present at the Au/Co interface. STM measurements and simulation of the local density of states reveal a magnetic band gap in the electronic structure of graphene for out-of-plane magnetization. This gap is promising for achieving a quantum anomalous Hall state in graphene.

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-xSn_xBi_2Te_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-xSn_xBi_2Te_4 as a tunable platform for tailoring electronic properties in spintronic and quantum technologies.

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) Mn_1-xGe_x Bi_2 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 Mn_1-xGe_x Bi_2 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).

The utilization of graphene on silicon carbide (SiC) substrates holds substantial promise for advancements in spintronics and nanoelectronics. Furthermore, incorporating magnetic metals provides an optimal framework for probing fundamental physical phenomena. The approach to developing such systems is in situ intercalation of graphene with magnetic metals. Herein, the electronic structure is analyzed and the magnetic properties of the system are synthesized by the thermal decomposition of 6H‐SiC(0001) surface and subsequent intercalation of graphene with cobalt (Co) and iron (Fe) atoms. X‐ray photoemission spectroscopy and low‐energy electron diffraction are employed to control the synthesis and metal intercalation processes. The morphological characteristics of the synthesized system are studied by means of atomic force microscopy. The findings derived from magneto‐optic Kerr effect measurements reveal a homogeneous ferromagnetic ordering at room temperature. Angle‐resolved photoemission spectroscopy is used to ascertain the impact of intercalation on graphene's electronic structure. The results of this study are essential for the development of graphene‐based spintronics and nanoelectronic devices as well as for fundamental studies in magnetic graphene systems.

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), an experimental andtheoretical study of changes in the electronic structure (dispersion dependencies) and corresponding modification of the energyband gap at the Dirac point (DP) for topological insulator (TI) Mn1−xGexBi2Te4 have been carried out with gradual replacementof magnetic Mn atoms by non-magnetic Ge atoms when concentration of the latter was varied from 10% to 75%. It was shownthat when Ge concentration increases then the bulk band gap decreases and reaches zero plateau in the concentration range of45%–60% while non-topological surface states (TSS) are present and exhibit an energy splitting of 100 and 70 meV in differenttypes of measurements. It was also shown that TSS disappear from the measured band dispersions at a Ge concentrationof about 40%. DFT calculations of Mn1−xGexBi2Te4 band structure were carried out to identify the nature of observed banddispersion features and to analyze a possibility of magnetic Weyl semimetal state formation in this system. These calculationswere 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 differentseries of topological phase transitions (TPTs) may be implemented in this system depending on the magnetic ordering. At AFMordering transition between TI and trivial insulator phase goes through the Dirac semimetal state, whereas for FM phase suchroute admits three intermediate states instead of one (TI — Dirac semimetal — Weyl semimetal — Dirac semimetal — trivialinsulator). Weyl points that form in FM system along the ΓZ direction annihilate when either the SOC strength decreases or asufficient tensile strain is applied, which is accompanied by the corresponding TPTs. Model calculations of local magneticordering influence in AFM Mn1−xGexBi2Te4 was carried out by alternating Mn layers and Ge-doped layers and showed that themagnetic Weyl semimetal state in this system is reachable at a Ge concentration of approximately 40% without application ofany external magnetic fields

We report on in si tu investigation of Au intercalation of differ ent zero -layer graphene surface reconstructions of V V V V V V V V 6 H -SiC(0001): ( 3x 3) R 30 degrees +(6 3x6 3) R 30 degrees , (6 3x6 3) R 30 degrees +(5x5) R 0 degrees , (6 3x6 3) R 30 degrees +(5x5) R 0 degrees +Gr. We show that the most appropriate reconstruction for graphene formation via Au intercalation is a one with some fraction of initial graphene monolayer. A well -ordered epitaxial Au(111) islands on the zero -layer graphene were revealed with the same crystallographic orientation as the SiC surface. Ab initio calculations approve that the value of Rashba splitting in graphene increases with the density of Au atoms per unit cell and with the reduction of average distance between Au and graphene.

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).

The surface spin-polarized states in the electronic structure of Pt(111) and graphene/Pt(111) have been studied in detail using angle-resolved photoelectron spectroscopy and density functional theory calculations. The results obtained show the presence of cone-shaped surface states near the Fermi level in the vicinity of the M̅ point of the surface Brillouin zone of platinum for both systems. Theoretical calculations confirm that these states are spin-polarized surface states of Pt(111) single crystal.

The influence of the size of dislocation loops on sublattice ferrimagnetism in graphene is studied. It is shown that graphene and the underlying gold layer with Au/Co dislocation loops of various sizes are characterized by ferrimagnetic ordering within atomic layers. Additional gold adatoms under graphene enhance the induced Rashba spin–orbit coupling in graphene but do not destroy the ferrimagnetic order in graphene. Since gold clusters can remain during the intercalation of gold on the surface of graphene and under graphene, the number and size of clusters after intercalation can be controlled to enhance the induced Rashba interaction and to obtain a topological phase in graphene.

We have analyzed different factors responsible for changes in the Dirac gap in MnBi2Te4 and the routes that determine the possibilities of the purposeful gap modulation. It was shown that upon changing the surface van der Waals interval and surface spin–orbit coupling strength the topological surface states localization shifts between the surface septuple layers with opposite magnetizations, which leads to a nonmonotonic change in the Dirac gap size. The minimum in the Dirac gap corresponds to the point of changing the sign of the emerging exchange field. Moreover, we have shown that the Dirac gap can be effectively modulated by replacing magnetic Mn atoms in the surface layer with nonmagnetic ones or Bi and Te atoms with atoms of elements with a lower spin–orbit coupling that makes it possible to create synthetic layered topological systems with purposeful modification of the surface properties.

The joint intercalation of Co and Fe atoms under a graphene buffer layer synthesized on a SiC(0001) single crystal has been studied. Intercalation has been performed by means of the alternating deposition of ultrathin Fe and Co metal films on the substrate heated to 450°C with the subsequent heating to 600°C in 15 min. It has been shown that Co and Fe atoms under these conditions are intercalated under graphene, forming compounds with silicon and with each other. The existence of a magnetic order in the system up to room temperature has been demonstrated using a superconducting quantum interferometer. A possible stoichiometry of the formed alloys has been analyzed using data on the shape and magnitude of hysteresis loops. In addition, it has been found that Fe and Co in the system exposed to the atmosphere are not oxidized. Thus, graphene protects the formed system. This study makes contribution to the investigation of graphene in contact with magnetic metals and promotes its application in spintronic and nanoelectronic devices.

Modification of graphene electronic properties via contact with atoms of different kind allows for designing a number of functional post-silicon electronic devices. Specifically, 2D metallic layer formation over graphene is a promising approach to improving the electronic properties of graphene-based systems. In this work we analyse the electronic and spin structure of graphene synthesized on Pt(111) after sodium monolayer adsorption by means of angle-resolved photoemission spectroscopy and ab initio calculations. Here, we show that sodium layer formation leads to a shift of the graphene π states towards higher binding energies, but the most intriguing property of the studied system is the appearance of a partially spin-polarized Kanji symbol-like feature resembling the graphene Dirac cone in the electronic structure of adsorbed sodium. Our findings reveal that this structure is caused by a strong interaction between Na orbitals and Pt $$5d$$ spin-polarized states, where the graphene monolayer between them serves as a mediator of such interaction.

Band structure and topology of magneto-spin–orbit graphene is investigated using the proposed tight-binding model that incorporates both Rashba and sublattice-resolved collinear exchange couplings in a generic ferrimagnetic (FIM) setting for in-plane and out-of-plane magnetization directions. The resulting band structures were analyzed for possibilities to extract the strengths of exchange and Rashba couplings from experimental spin-resolved ARPES measurements of the valley gaps and π-state spin-splittings. It was shown that the topologically trivial in-plane FIM situation admits simple expressions for these quantities, whereas the out-of-plane FIM, which admits a nontrivial band topology, is harder to analyze. The obtained topological phase diagrams for the out-of-plane FIM case show that the anomalous Hall conductance is quite stable with respect to the antiferromagnetic (AFM) interaction, which tends to interfere with the QAHE phase; moreover, the topological phase transition has a rather smooth character with respect to the AFM coupling strength.

Intercalation of noble metals can produce giant Rashba-type spin–orbit splittings in graphene. The spin–orbit splitting of more than 100 meV has yet to be achieved in graphene on metal or semiconductor substrates. Here, we report the p-type graphene obtained by Pt intercalation of zero-layer graphene on SiC substrate. The spin splitting of ∼200 meV was observed at a wide range of binding energies. Comparing the results of theoretical studies of different models with the experimental ones measured by spin-ARPES, XPS and STM methods, we concluded that inducing giant spin–orbit splitting requires not only a relatively close distance between graphene and Pt layer but also the presence of graphene corrugation caused by a non-flat Pt layer. This makes it possible to find a compromise between strong hybridization and increased spin–orbit interaction. In our case, the Pt submonolayer possesses nanometer-scale lateral ordering under graphene.

The possibility of significant modulation of the band gap open at the Dirac point (DP) in the range from 15 to 55 meV for different samples of the antiferromagnetic topological insulator MnBi2Te4 is shown using angle-resolved photoemission spectroscopy. The density functional theory is used to analyze the relation between the gap at the DP and the surface potential gradient, the change of which is modeled by the application of an electric field normal to the (0001) MnBi2Te4 surface. The possibility of both decreasing and increasing the DP gap in the range from 5 to 89 meV with respect to the initial value of 81 meV due to the application of a field is shown. When a field is applied, the localization of topological surface states and the magnetic moments of surface atoms change. Our analysis demonstrates the possibility of an artificial band gap modulation at the DP over a wide energy range, which can be used to modulate the magnetoelectric properties of MnBi2Te4-based systems in applied research and problems.

We analyze the synthesis of the buffer carbon layer on a SiC(0001) single crystal and its subsequent intercalation with cobalt atoms. It is shown using X-ray photoelectron spectroscopy that the intercalation is accompanied with the formation of a surface cobalt silicide alloy under the quasi-free graphene. The data measured using angle-resolved photoelectron spectroscopy demonstrate the presence of a Dirac cone near the Fermi level, which confirms the formation of quasi-free graphene as a result of intercalation. The morphology and homogeneity of the resulting system have been investigated using atomic force microscopy and Raman spectroscopy. The features of the graphene band structure on possible cobalt silicide alloys have been investigated using the density functional theory. The calculations of the chemical shift of the 2p level of Si for cobalt silicides confirm the presence of CoSi and CoSi2 components in X-ray photoelectron spectroscopy data. It is shown that the formation of quasi-free graphene with a linear dispersion of the π states is possible only on the CoSi surface. In view of the importance of investigation of graphene on insulating substrates as well as unique properties of graphene in contact with magnetic metals, we hope that this study will make a contribution to further realization of graphene in spintronics and nanoelectronics devices.

This work is devoted to an experimental investigation of the electronic structure of the surface of topological insulators of various stoichiometry during the adsorption of Co atoms. Changes in the surface electronic structure of Bi2Te3 and MnBi2Te4 systems upon deposition of Co atoms at various temperatures have been studied using the methods of angle-resolved photoemission spectroscopy, as well as X-ray photoelectron spectroscopy. It is suggested that binding of the adsorbed Co atoms to the substrate surface modifies Dirac point position. The observed changes are associated with the possible formation of magnetic Co-containing ordered surface alloys.