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Polar Rashba-type semiconductor BiTeI doped with magnetic elements constitutes one of the most promising platforms for the future development of spintronics and quantum computing thanks to the combination of strong spin-orbit coupling and internal ferromagnetic ordering. The latter originates from magnetic impurities and is able to open an energy gap at the Kramers point (KP gap) of the Rashba bands. In the current work using angle-resolved photoemission spectroscopy (ARPES) we show that the KP gap depends non-monotonically on the doping level in case of V-doped BiTeI. We observe that the gap increases with V concentration until it reaches 3% and then starts to mitigate. Moreover, we find that the saturation magnetisation of samples under applied magnetic field studied by superconducting quantum interference device (SQUID) magnetometer has a similar behaviour with the doping level. Theoretical analysis shows that the non-monotonic behavior can be explained by the increase of antiferromagnetic coupled atoms of magnetic impurity above a certain doping level. This leads to the reduction of the total magnetic moment in the domains and thus to the mitigation of the KP gap as observed in the experiment. These findings provide further insight in the creation of internal magnetic ordering and consequent KP gap opening in magnetically-doped Rashba-type semiconductors.

We show that graphene can be magnetized by coupling to a ferromagnetic Co film through a Au monolayer. The presence of dislocation loops under graphene leads to a ferrimagnetic ordering of moments in the two C sublattices. It is shown that the band gap of ∼80 meV in the K[over ¯] point has a magnetic nature and exists for ferrimagnetic ordering. Interplay between Rashba and exchange couplings is evidenced by spin splitting asymmetry in spin-ARPES measurements and fully supported by DFT calculation of a (9×9) unit cell. Owing to sign-opposite Berry curvatures for K[over ¯] and K[over ¯]^{'} valleys, the synthesized system is promising for the realization of a circular dichroism Hall effect.

The influence of manganese atom intercalation on the electronic structure of graphene grown on Au/Co(0001)/W(110) and SiC(0001) substrates is experimentally studied by angle-resolved photoelectron spectroscopy. Dispersion dependences of the graphene π states at the $$\bar {K}$$ point of the Brillouin zone are obtained for both systems using ultraviolet photoelectron spectroscopy, and these dependences exhibit shifts of the Dirac cone induced by manganese intercalation followed by annealing. The structure of the near-surface layers of the systems is investigated by X-ray photoelectron spectroscopy. An analysis of the core level lines indicates the possibility of formation of a thin Mn2Au layer on the graphene–Mn–Au interface and a quasi-two-dimensional Mn layer under graphene on the SiC substrate. A comprehensive Raman spectroscopy study of graphene on SiC demonstrates that the buffer layer remains coupled to the substrate and does not transform into an additional graphene layer after the Mn intercalation of this system. After intercalation, the amount of lattice defects in graphene increases.

It is shown for the first time that Co subnanometer coatings deposited by molecular-beam epitaxy on the (0001) surface of the topological insulator BiSbTeSe2 at a temperature of 330°C open an energy gap in the spectrum of topological surface states in the region of the Dirac point with a shift of the Dirac-point position caused by the preliminary deposition of an adsorbate at room temperature. The gap width is 21 ± 6 meV. Temperature-dependent measurements in the range of 15–150 K show no changes in the energy-gap width.

Recently discovered intrinsic antiferromagnetic topological insulator $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ Dirac cone. Here, using micro($\ensuremath{\mu}$)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the N\'eel temperature at about 10--16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ DP gap size.

The electronic structure of magnetically doped topological insulator Bi1.09Gd0.06Sb0.85Te3 is studied in the vicinity of the Dirac point at various temperatures (above and below the Neel temperature, 1–35 K) and synchrotron radiation polarizations using angle-resolved photoelectron spectroscopy. It is shown that the energy gap exists in photoemission spectra at the Dirac point, which remains open above the long-range magnetic ordering temperature TN. Measurements of magnetic properties by the superconducting magnetometry method show antiferromagnetic ordering with the paramagnetic transition temperature of 8.3 K. The studies of the temperature dependence of the Dirac cone state intensity by photoelectron spectroscopy confirm the existence of the magnetic transition and show the possibility of its indication directly from photoemission spectra. A more detailed analysis of the splitting between states of upper and lower Dirac cones (i.e., the energy gap) at the Dirac point in the photoelectron spectra shows the dependence of the gap at the Dirac point on the synchrotron radiation polarization type (28–30 meV for p-polarization and 22–25 meV for circularly polarized radiation of opposite chirality). The gap opening mechanism at the Dirac point above TN due to “coupling” of Dirac fermions with opposite momenta and spin orientations due to their interaction with the spin texture formed immediately during photoemission in the region of the photoemission hole at the magnetic impurity atom (Gd). It is shown that the gap at the Dirac point, measured above TN, is dynamic and is formed immediately during photoemission. In this case, the gap nature remains magnetic (even in the absence of long-range magnetic ordering) and is caused by properties of magnetic topological insulator, which does control the gap invariability when passing through TN. The dynamic nature of the generated gap is confirmed by its dependence on synchrotron radiation polarization.

The recent realization of quantum anomalous Hall effect and Majorana fermions observation enhance interest in magnetism investigation in topological insulators. In this work, the electronic and magnetic structure of the Gd-doped topological insulator Bi1.09Gd0.06Sb0.85Te3 were systematically studied by means of angle-resolved photoemission spectroscopy, resonance photoemission spectroscopy (ResPES) and SQUID magnetometry. Resonant features related to the Gd density of states near the Fermi level are experimentally observed. Study of magnetic structure showed antiferromagnetic ordered bulk at low temperatures as well as presence of hysteresis loop at elevated temperatures. Finally, possible mechanism of magnetism and its relation to observed electronic features are discussed.

Graphene electronics covers a number of unique effects and the most intriguing ones are based on its interaction with other materials. Contact of graphene with the lattice-mismatched substrate clones the Dirac cone and gives rise to Hofstadter spectrum, while contact with the heavy/magnetic atoms realizes topological insulator phase. Here we study the electronic structure of graphene on Ir(111) with intercalated rare-earth Gd atoms by means of Angle-Resolved Photoemission Spectroscopy (ARPES). Gd intercalation results in the formation of the Gd-Ir surface alloy with the (2 × 2) superstructure, but the moire superlattice of graphene persists. Strong charge transfer from Gd atoms leads to the shifting of the Dirac cone and its replicas towards the higher binding energies while closing the u m k l a p p band gaps. The replicated Dirac cone bands cross each other near the Fermi level, that is essential for the superlattice effects application in electronics.

Modification of the electronic and crystal structure of zero-layer graphene grown on $6H$-SiC(0001) after Co intercalation is reported. Using a wide range of techniques including angle-resolved photoelectron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, low-energy electron diffraction, we found that zero-layer graphene on SiC transforms into graphene monolayer as a result of cobalt intercalation. The Dirac cone of $\ensuremath{\pi}$ band characteristic of quasi-freestanding graphene is observed. In combination with high-resolution transmission electron microscopy and atomic force microscopy data, we conclude that ultrathin silicide $\mathrm{CoSi}\text{/}{\mathrm{CoSi}}_{2}$ structure is formed between graphene and SiC substrate. Investigation of magnetic properties reveals ferromagnetic behavior with open hysteresis loop. The results of this work are the basis for further implementation of magneto-spin-orbit graphene on a semiconducting substrate and are important for the future application of such graphene in spintronics.

Narrow-gap semiconductors with strong spin-orbit coupling such as bismuth tellurohalides have become popular candidates for spintronic applications. But driving spin-polarized photocurrents in these materials with circularly polarized light requires picosecond lifetimes of the photoexcited carriers and low spin-flip scattering rates. In search of these essential ingredients, we conducted an extensive study of the carrier dynamics on the Te-terminated surface of BiTeI, which exhibits a giant Rashba splitting of both surface and bulk states. We observe a complex interplay of surface and bulk dynamics after photoexcitation. Carriers are rapidly rearranged in momentum space by quasielastic phonon and defect scattering, while a phonon bottleneck leads to a slow equilibration between bulk electrons and lattice. The particular band dispersion opens an inelastic decay channel for hot carriers in the form of plasmon excitations, which are immanent to Rashba-split systems. These ultrafast scattering processes effectively redistribute excited carriers in momentum and energy space and thereby inhibit spin-polarized photocurrents., This project was supported by the German Research Foundation via the Collaborative Research Center TRR 227 on Ultrafast Spin Dynamics, project A1, and the German-Russian Interdisciplinary Science Center (GRISC). A.S.K. is indebted to the International Max Planck Research School Functional Interfaces in Physics and Chemistry for financial support. B.A. and V.V. acknowledge travel support by GRISC. O.E.T. and K.A.K. were supported by the Russian Science Foundation (Project No. 17-12-01047) and a state contract of ISP and IGM SB RAS. A.S. acknowledges support by Russian Science Foundation (Grant No. 18-12-00062). A.S. and E.V.C. acknowledge support by the Saint Petersburg State University (Grant No. ID 73028629).

Effect of magnetization generated by synchrotron or laser radiation in magnetically-doped and pristine topological insulators (TIs) is presented and analyzed using angle-resolved photoemission spectroscopy. It was found that non-equal photoexcitation of the Dirac cone (DC) states with opposite momenta and spin orientation indicated by the asymmetry in photoemission intensity of the DC states is accompanied by the k||-shift of the DC states relative to the non-spin-polarized conduction band states located at k|| = 0. We relate the observed k||-shift to the induced surface in-plane magnetic field and corresponding magnetization due to the spin accumulation. The direction of the DC k||-shift and its value are changed with photon energy in correlation with variation of the sign and magnitude of the DC states intensity asymmetry. The theoretical estimations describe well the effect and predict the DC k||-shift values which corroborate the experimental observations. This finding opens new perspectives for effective local magnetization manipulation.

The effect of an ultrathin Pb film deposited on the surface of Bi2Se3 and Sb2Te3 compounds on the electronic state structure of topological insulators is studied experimentally by the angle-resolved photoemission spectroscopy (ARPES) technique. The following features are revealed: formation of two-dimensional quantum-well states in the near-surface region, an increase in the binding energy of the Dirac cone and the core levels, and a simultaneous electronic states intensity redistribution in the system in photoemission spectra. The results obtained show that topological states may coexist at the interface between studied materials and a superconductor, which seems to be promising for application in quantum computers.

A detailed study of graphene growth process via segregation of carbon atoms through a 16 nm-thick metal film is presented. Two different transition metals – Co and Ni – are deposited on a highly-oriented pyrolytic graphite (HOPG) substrate. It is demonstrated that annealing of the systems leads to segregation of carbon atoms from the substrate to the surface. X-ray photoemission studies show that in both cases a metal-rich carbide phase is formed in a near-surface area, which after a low-temperature annealing transforms into carbon-rich carbide phase. After further increase of the annealing temperature this carbide phase is transformed into graphene mono- and multilayers. Low energy electron diffraction measurements show that at the final stage a large part of the sample is covered with highly-ordered graphene domains, however a lot of small variously oriented domains can also be seen. It is shown that graphene on Co/HOPG is formed at comparable temperatures to that on Ni/HOPG, and it has better ordered surface.

The control of the graphene electronic structure is one of the most important problems in modern condensed matter physics. The graphene monolayer synthesized on the Re(0001) surface and then subjected to the intercalation of Pb atoms is studied by angle-resolved photoelectron spectroscopy and low-energy electron diffraction. The intercalation of Pb atoms under graphene takes place when the substrate is annealed above 500°C. As a result of the intercalation of Pb atoms, graphene becomes quasi-free-standing and a local band gap appears at the Dirac point. The band gap changes with the substrate temperature during the formation of the graphene/Pb/Re(0001) system. The band gap is 0.3 eV at an annealing temperature of 620°C and it increases up to 0.4 eV upon annealing at 830°C. Based on our data, we conclude that the band gap is mainly caused by the hybridization of the graphene π state with the rhenium 5d states located near the Dirac point of the graphene π state.

Modification of the gap at the Dirac point (DP) in axion antiferromagnetic topological insulator MnBi2Te4 and its electronic and spin structure have been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation at various temperatures (9–35 K), light polarizations and photon energies. We have distinguished both large (60–70 meV) and reduced (, The authors acknowledge support by the Saint Petersburg State University (Grant No. 51126254), Russian Science Foundation (Grant No. 18-12-00062 in part of the photoemission measurements and Grant No. 18-12-00169 in part of the electronic band structure calculations) and by Russian Foundation of Basic Researches (Grants Nos. 18-52-06009 and 20-32-70179) and Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02). A. Kimura was financially supported by KAKENHI (Grants No. 17H06138, No. 17H06152, and No. 18H03683). S.V.E. and E.V.C. acknowledge support by the Fundamental Research Program of the State Academies of Sciences (line of research III.23.2.9). The authors kindly acknowledge the HiSOR staff and A. Harasawa at ISSP for technical support and help with the experiment. The ARPES measurements at HiSOR were performed with the approval of the Proposal Assessing Committee (Proposal Numbers: 18BG027 and 19AG048). XAS and XMCD measurements were performed at BL23SU of SPring-8 (Proposal Nos. 2018A3842 and 2018B3842) under the Shared Use Program of JAEA Facilities (Proposal Nos. 2018A-E25 and 2018B-E24) with the approval of Nanotechnology Platform project supported by MEXT, Japan (Proposal Nos. A-18-AE-0020 and A-18-AE-0042). M. M. Otrokov acknowledges the support by Spanish Ministerio de Ciencia e Innovacion (Grant no. PID2019-103910GB-I00). K. Yaji was financially supported by KAKENHI (Grants No. 18K03484).

Feasibility of many emergent phenomena that intrinsic magnetic topological insulators (TIs) may host depends crucially on our ability to engineer and efficiently tune their electronic and magnetic structures. Here we report on a large family of intrinsic magnetic TIs in the homologous series of the van der Waals compounds (MnBi2Te4)(Bi2Te3)m with m = 0, ⋯, 6. Magnetic, electronic and, consequently, topological properties of these materials depend strongly on the m value and are thus highly tunable. The antiferromagnetic (AFM) coupling between the neighboring Mn layers strongly weakens on moving from MnBi2Te4 (m = 0) to MnBi4Te7 (m = 1) and MnBi6Te10 (m = 2). Further increase in m leads to change of the overall magnetic behavior to ferromagnetic (FM) one for (m = 3), while the interlayer coupling almost disappears. In this way, the AFM and FM TI states are, respectively, realized in the m = 0, 1, 2 and m = 3 cases. For large m numbers a hitherto-unknown topologically nontrivial phase can be created, in which below the corresponding critical temperature the magnetizations of the non-interacting 2D ferromagnets, formed by the MnBi2Te4 building blocks, are disordered along the third direction. The variety of intrinsic magnetic TI phases in (MnBi2Te4)(Bi2Te3)m allows efficient engineering of functional van der Waals heterostructures for topological quantum computation, as well as antiferromagnetic and 2D spintronics., This work is supported by Saint Petersburg State University project for scientific investigations (ID No. 51126254, https://spin.lab.spbu.ru) and Russian Science Foundation (Grant no. 18-12-00062 in part of the photoemission measurements and 18-12-00169 in part of calculations of topological invariants, investigation of dependence of the electronic spectra on SOC strength, and tight-binding band structure calculations). Russian Foundation for Basic Research (Grant nos. 20-32-70179 and 18-52-06009) and Science Development Foundation under the President of the Republic of Azerbaijan (Grant no. EIF-BGM-4-RFTF-1/2017-21/04/1-M-02) are acknowledged. We also acknowledge the support by the Basque Departamento de Educacion, UPV/EHU (Grant no. IT-756-13), Spanish Ministerio de Ciencia e Innovación (Grant no. PID2019-103910GB-I00), the Fundamental Research Program of the State Academies of Sciences (line of research III.23.2.9) and Tomsk State University competitiveness improvement program (project no. 8.1.01.2018). I.P.R. acknowledge support from Ministry of Education and Science of the Russian Federation (State Task No. 0721-2020-0033) (tight-binding calculations). The calculations were performed in Donostia International Physics Center and in the Research park of St. Petersburg State University Computing Center (http://cc.spbu.ru).

This work is supported by the Russian Science Foundation (Grants No. 18-12-00169 in part of the density functional calculations and No. 18-12-00062 in part of the photoemission measurements) and Saint Petersburg State University (Grant ID 40990069). The support from the Academic D.I. Mendeleev Fund Program of Tomsk State University (Project No. 8.1.01.2018), the Russian Foundation for Basic Researches (Grant No. 18-52-06009), the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EIF/MQM/Elm-Tehsil-1-2016-1(26)-71/01/4-M33), the Basque Country Government, Departamento de Educacion, Universidades e Investigacion (Grants No. IT-756-13 and No. IT1301-19) and the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2016-75862-P) are acknowledged. J.S.-B. gratefully acknowledges financial support from the Impuls-und Vernetzungsfonds der Helmholtz-Gemeinschaft under Grant No. HRSF-0067 (Helmholtz-Russia Joint Research Group). Calculations were partly performed using computational resources provided by Resource Center “Computer Center of SPbU” (http://cc.spbu.ru) and the SKIFCyberia sup

Angle-resolved secondary electron emission spectra were analyzed for studying the electron transmission properties of graphene when it is tightly bound to a metallic substrate and when it is decoupled from the latter. As respective model systems, graphene/Ni(111) and graphene/Au/Ni(111) were considered. We discovered two types of spectral structures linked with the transmission properties of graphene: bands related to scattering resonances and to umklapp reflection. These findings are interpreted based on an ab initio theory of the scattering of the outgoing electrons by the graphene overlayers. The experimental secondary electron emission maps are in good agreement with the calculations, indicating that such approach can be successfully applied for studying the electron transmission properties of a variety of two-dimensional materials.

A new kind of magnetically-doped antiferromagnetic (AFM) topological insulators (TIs) with stoichiometry Bi1.09Gd0.06Sb0.85Te3 has been studied by angle-resolved photoemission spectroscopy (ARPES), superconducting magnetometry (SQUID) and X-ray magnetic circular dichroism (XMCD) with analysis of its electronic structure and surface-derived magnetic properties at different temperatures. This TI is characterized by the location of the Dirac gap at the Fermi level (EF) and a bulk AFM coupling below the Neel temperature (4–8 K). At temperatures higher than the bulk AFM/PM transition, a surface magnetic layer is proposed to develop, where the coupling between the magnetic moments located at magnetic impurities (Gd) is mediated by the Topological Surface State (TSS) via surface Dirac-fermion-mediated magnetic coupling. This hypothesis is supported by a gap opening at the Dirac point (DP) indicated by the surface-sensitive ARPES, a weak hysteresis loop measured by SQUID at temperatures between 30 and 100 K, XMCD measurements demonstrating a surface magnetic moment at 70 K and a temperature dependence of the electrical resistance exhibiting a mid-gap semiconducting behavior up to temperatures of 100–130 K, which correlates with the temperature dependence of the surface magnetization and confirms the conclusion that only TSS are located at the EF. The increase of the TSS’s spectral weight during resonant ARPES at a photon energy corresponding to the Gd 4d-4f edge support the hypothesis of a magnetic coupling between the Gd ions via the TSS and corresponding magnetic moment transfer at elevated temperatures. Finally, the observed out-of-plane and in-plane magnetization induced by synchrotron radiation (SR) due to non-equal depopulation of the TSS with opposite momentum, as seen through change in the Dirac gap value and the k∥-shift of the Dirac cone (DC) states, can be an indicator of the modification of the surface magnetic coupling mediated by the TSS.

Graphene is one of the most promising materials for nanoelectronics owing to its unique Dirac cone-like dispersion of the electronic state and high mobility of the charge carriers. However, to facilitate the implementation of the graphene-based devices, an essential change of its electronic structure, a creation of the band gap should controllably be done. Brought about by two fundamentally different mechanisms, a sublattice symmetry breaking or an induced strong spin-orbit interaction, the band gap appearance can drive graphene into a narrow-gap semiconductor or a 2D topological insulator phase, respectively, with both cases being technologically relevant. The later case, characterized by a spin-orbit gap between the valence and conduction bands, can give rise to the spin-polarized topologically protected edge states. Here, we study the effect of the spin-orbit interaction enhancement in graphene placed in contact with a lead monolayer. By means of angle-resolved photoemission spectroscopy, we show that intercalation of the Pb interlayer between the graphene sheet and the Pt(111) surface leads to formation of a gap of 200 meV at the Dirac point of graphene. Spin-resolved measurements confirm the splitting to be of a spin-orbit nature, and the measured near-gap spin structure resembles that of the quantum spin Hall state in graphene, proposed by Kane and Mele [ Phys. Rev. Lett. 2005, 95, 226801 ]. With a bandstructure tuned in this way, graphene acquires a functionality going beyond its intrinsic properties and becomes more attractive for possible spintronic applications., The work was partially supported by grants from Saint Petersburg State University for scientific investigations (Nos. 11.38.271.2014 and 15.61.202.2015) and DFG - SPbU grant No. 11.65.42.2017. We acknowledge financial support from the University of Basque Country UPV/EHU (Grant No. GIC07-IT-756-13), the Departamento de Educacion del Gobierno Vasco and the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2010-19609-C02-01), the Spanish Ministry of Economy and Competitiveness MINECO (Grant No. FIS2013-48286-C2-1-P), and the Tomsk State University Academic D. I. Mendeleev Fund Program in 2015 (Research Grant No. 8.1.05.2015).

A comparative investigation of graphene prepared by cracking of propylene (C3H6) on nickel surfaces with different orientations, Ni(111) and Ni(100), has been carried out using angle-resolved photoemission spectroscopy. It has been shown that the graphene formed on the Ni(111) surface is well ordered on a large surface area, whereas the graphene on the Ni(100) surface has a well-defined domain structure. It has been found that the electronic structures of the two systems are similar to each other, and graphene is strongly bound to the nickel substrate. It has been demonstrated that the intercalation of a gold monolayer for the two systems leads to the formation of an electronic structure that is characteristic of quasi-free-standing graphene.

An experimental study of the graphene, synthesized by propylene cracking on Ni surfaces with different orientation: (100) and (111), using angle-resolved photoemission, has been performed. It has been shown that graphene on Ni(111) had a perfect lateral structure due to consistency of their lattices, whereas graphene/Ni(100) consisted of a lot of domains. For both systems electronic structure was quite similar and demonstrated a strong bonding of graphene to the underlying Ni surface. After Au intercalation the electronic structure of graphene in both systems was shifted to the Fermi level and became linear in the vicinity of the K point of the Brillouin zone.

A new method for generating spin-polarized currents in topological insulators has been proposed and investigated. The method is associated with the spin-dependent asymmetry of the generation of holes at the Fermi level for branches of topological surface states with the opposite spin orientation under the circularly polarized synchrotron radiation. The result of the generation of holes is the formation of compensating spin-polarized currents, the value of which is determined by the concentration of the generated holes and depends on the specific features of the electronic and spin structures of the system. The indicator of the formed spin-polarized current can be a shift of the Fermi edge in the photoelectron spectra upon photoexcitation by synchrotron radiation with the opposite circular polarization. The topological insulators with different stoichiometric compositions (Bi1.5Sb0.5Te1.8Se1.2 and PbBi2Se2Te2) have been investigated. It has been found that there is a correlation in the shifts and generated spin-polarized currents with the specific features of the electronic spin structure. Investigations of the graphene/Pt(111) system have demonstrated the possibility of using this method for other systems with a spin-polarized electronic structure.

Synthesis of a graphene monolayer atop Ni(111) film deposited on HOPG using method of “internal solid-state carbon source” due to low-temperature segregation of carbon atoms through Ni film from the Ni/HOPG interface was studied by core level and valence band photoelectron spectroscopy. The atomic structure and morphology were studied by STM. It was established that the synthesis of graphene occurs via a stage of transformation from the surface carbide phase (with stoichiometry Ni2C) as a result of the surface carbide decomposition. We consider that such transformation is a necessary stage of the graphene synthesis. We have shown that the method of “solid-state carbon source” indeed results in a graphene monolayer formation on top of Ni film. A graphene monolayer begins to form even under annealing at 180 °C. Formation of practically full graphene covering with well-ordered structure takes place even at temperature of 260–270 °C. The formed graphene is strongly coupled to the Ni substrate. STM images show formation of well-ordered atomic hexagonal surface structure characteristic for graphene monolayer. Intercalation of Au atoms leads to formation of the p(9 × 9) superstructure and blocks strong coupling. It testifies that the main part of the surface is covered by epitaxial graphene on Ni. Keywords: Graphene, Segregation, Synthesis, Carbide phase, Intercalation

The energy gap was revealed in the Dirac cone of the BiSbTeSe2 topological insulator after the submonolayer deposition of a ferromagnetic metal. As a ferromagnet, cobalt and manganese were used. Such way of the energy gap opening is novel in comparison to the bulk ferromagnetic doping of topological insulators.

In the present study we synthesized nano-thin epitaxial Pt x Gd alloys on Pt(111) single crystal surface covered with well-oriented graphene and investigated their electronic and atomic structure at different stages of synthesis. Low-energy electron diffraction, photoelectron spectroscopy and scanning tunneling microscopy data suggest that deposition of Gd on the graphene/Pt(111) system and its further intercalation at 1080 ° C lead to formation of nano-thin Pt 5 Gd alloy covered with a quasi-freestanding graphene. We demonstrate that atomically flat alloy surface is terminated by Pt atomic layer with “kagome” structure. Control of graphene doping through variation of the alloy stoichiometry may open up new opportunities in developing advanced electronics. Owing to a well-known catalytic activity of Pt 5 Gd alloy, our thin-film system is promising for low-cost production of catalysts in the near future.

Narrow bandgap BiSe, BiTe, and SbTe, commonly referred to as classic 3D topological insulators, were studied at room temperature by spectroscopic ellipsometry and optical reflection spectroscopy over the mid-IR-near-infrared photon energy range. Complementarily, Hall measurements were performed. Plasmons in optical loss function and reflection coefficient were identified. The conventional approach based on the high frequency dielectric constant was shown to work well in the description of plasmons in BiSe and SbTe and to fail in the case of a similar compound, BiTe. The obtained results are discussed in terms of single- and multivalley approaches to the studied samples with taking the details of the calculated band structure into account., This work was supported by the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02 and EİF-BGM-3-BRFTF-2+/2017-15/02/1), the Russian Foundation for Basic Research (Grant No. 18-52-06009), and the Saint Petersburg State University grant for scientific investigations (Grant No. 15.61.202.2015).

Possibility of in-plane and out-of-plane magnetization generated by synchrotron radiation (SR) in magnetically doped and pristine topological insulators (TIs) is demonstrated and studied by angle-resolved photoemission spectroscopy. We show experimentally and by ab initio calculations how nonequal depopulation of the Dirac cone (DC) states with opposite momenta in V-doped and pristine TIs generated by linearly polarized SR leads to the hole-generated uncompensated spin accumulation followed by the SR-induced magnetization via spin-torque effect. Moreover, the photoexcitation of the DC is asymmetric, and it varies with the photon energy. We find a relation between the photoexcitation asymmetry, the generated spin accumulation, and the induced in-plane and out-of-plane magnetic field. Experimentally the SR-generated in-plane and out-of-plane magnetization is confirmed by the k∥ shift of the DC position and by the gap opening at the Dirac point even above the Curie temperature. Theoretical predictions and estimations of the measurable physical quantities substantiate the experimental results., The authors acknowledge support by Saint Petersburg State University (Grant No. 15.61.202.2015), Russian Science Foundation Grant No. 17-12-01333 (in the part of theoretical study of magnetic properties), Russian Science Foundation Grant No. 18-12-00062 (in the part of ARPES measurements and analysis of the electronic structure modification under influence of SR), and Russian Science Foundation Grant No. 17-12-01047 (in part of crystal growth and the sample characterization). The work was also supported by the Spanish Ministry of Economy and Competitiveness MINECO (Project No. FIS2016-76617-P), German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD), and Russian-German laboratory atBESSYII (Helmholtz-Zentrum Berlin).

The formation of graphene on the surface of a Gd film on a highly oriented pyrolytic graphite substrate has been studied by photoelectron spectroscopy using synchrotron radiation. It has been demonstrated that the formation of graphene passes through the phase of gadolinium carbidization, which is transformed with increasing annealing temperature. It has been established that, at a temperature of 1300 K, gadolinium carbide with the Gd2C3 stoichiometry is transformed into the carbide with the GdC2 stoichiometry. The analysis of all transient phase processes has been performed on the basis of the fine structure of photoelectron lines and dispersion of electron states. It has been shown that the Dirac cone of electron states of graphene is retained.

By angle- and spin-resolved photoemission we have studied electronic structure and spin–orbit splitting in graphene/Ni(1 1 1) intercalated with alloy of high spin–orbit materials Bi and Au. Results are compared to ultimate cases of (i) graphene/Ni intercalated only with Au which shows giant Rashba splitting ( ∼ 100 meV) and (ii) graphene/Ni intercalated only with Bi for which spin splitting of the Dirac cone is nearly zero ( ⩽ 10 meV). Our results demonstrate that partial substitution of intercalated Au with Bi reduces spin splitting of the Dirac cone in graphene and even allows for its systematic adjustment through concentration of Bi. Observed effects are ascribed to peculiar electronic structure of Bi which has in the valence band no d electronic states responsible for the onset of giant Rashba effect through electronic hybridization with π band of graphene. We also report in details electronic properties of graphene/Ni(1 1 1) intercalated only with Bi in various concentrations. Such graphene reveals undistorted band structure characteristic to quasifreestanding graphene with small n-doping and a minor band gap at the Dirac point ( ∼ 200 meV) which depends weakly on the concentration of Bi. It has been shown that this gap is related to the symmetry breaking rather than to the topological phase formation.

The formation of graphene on the surface of a nickel thin film on a highly oriented pyrolytic graphite substrate has been investigated using the photoelectron spectroscopy methods. It has been shown that the formation of graphene occurs through the phase of surface nickel carbide with the Ni2C stoichiometry, which is formed already at a temperature of 180°C. During the subsequent heating, the nickel carbide phase transforms into a graphene monolayer strongly bound to the surface. All the phase transitions have been thoroughly analyzed in terms of the fine structure of the photoelectron lines. The surface morphology has been examined using atomic force microscopy, and the obtained data have been presented. It has been especially emphasized that the advantage of the studied method of a “solid-state” source of carbon is the possibility of the formation of graphene at lower temperatures (at least no higher than 280°C) as compared to the cracking of carbon-containing gases, which requires the temperature ranging from 400 to 500°C.

A rich class of spintronics-relevant phenomena require implementation of robust magnetism and/or strong spin-orbit coupling (SOC) to graphene, but both properties are completely alien to it. Here, we for the first time experimentally demonstrate that a quasi-freestanding character, strong exchange splitting and giant SOC are perfectly achievable in graphene at once. Using angle- and spin-resolved photoemission spectroscopy, we show that the Dirac state in the Au-intercalated graphene on Co(0001) experiences giant splitting (up to 0.2 eV) while being by no means distorted due to interaction with the substrate. Our calculations, based on the density functional theory, reveal the splitting to stem from the combined action of the Co thin film in-plane exchange field and Au-induced Rashba SOC. Scanning tunneling microscopy data suggest that the peculiar reconstruction of the Au/Co(0001) interface is responsible for the exchange field transfer to graphene. The realization of this "magneto-spin-orbit" version of graphene opens new frontiers for both applied and fundamental studies using its unusual electronic bandstructure., The authors acknowledge support by the Saint Petersburg State University (Grant 15.61.202.2015), German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD) and Russian-German laboratory at BESSY II (Helmholtz-Zentrum Berlin). The funding by the University of the Basque Country (Grants GIC07IT36607 and IT-756-13), the Spanish Ministry of Science and Innovation (Grants FIS2013-48286-C02-02-P, FIS2013-48286-C02-01-P, and FIS2016-75862-P) and Tomsk State University competitiveness improvement programme (Project No. 8.1.01.2017) is also gratefully acknowledged. I.P.R. acknowledges support by the Ministry of Education and Science of the Russian Federation within the framework of the governmental program “Megagrants” (state task no. 3.8895.2017/P220).

A combined scanning tunneling microscopy, angle- and spin-resolved photoemission spectroscopy and density functional theory study of graphene on Ir(1 1 1) intercalated with a well-ordered, full Pb monolayer is presented. Lead intercalation between graphene and Ir(111) reduces the coupling to the metallic substrate in such a way that its corrugation becomes negligible and distortions of the linear dispersion largely disappear, while graphene's sublattice symmetry is maintained and it turns out to be n-doped. Remarkably, the spin–orbit splittings induced by the proximity of the Ir(1 1 1) surface are preserved after Pb intercalation in a wide energy range. We further show that the Pb/Ir(1 1 1) surface induces a complex spin texture with both in-plane and out-of-plane components. Our calculations reveal the origin of the out-of-plane spin components in graphene to trace back to the out-of-plane spin-polarized surface and resonance states of Ir(1 1 1), while the Pb interlayer on its own does not induce any vertical spin polarization in the carbon sheet. However, the Brillouin zone folding imposed by the rectangular symmetry of the intercalated Pb layer plays an instrumental role in the spin–orbit coupling (SOC) transfer to graphene, as well as in the linearization of its bands. Finally, since no sizeable gap is observed at the Dirac point, we suggest that an intrinsic (Kane and Mele type) SOC does not exceed the extrinsic (Rashba) SOC for graphene on Pb/Ir(111)., We acknowledge the support by the Basque Departamento de Educacion, UPV/EHU (Grant No. IT-756-13), Spanish Ministerio de Economia y Competitividad (MINECO Grants No. FIS2016- 75862-P, MAT2015-66888-C3-1R and FIS2015-67367-C2-1-P), Comunidad de Madrid (MAD2DCM and Nanofrontmag) and Tomsk State University competitiveness improvement programme (project No. 8.1.01.2017). The support by the Saint Petersburg State University (Grant No. 15.61.202.2015) and Russian Foundation for Basic Research (Grant No. 18-32-00145) are also acknowledged. The part of photoemission measurements had been supported by Russian Science Foundation Grant No. 18-12-00062. IMDEA Nanociencia acknowledges support from the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686).

Detailed comparative theoretical and experimental study of electronic properties and spin structure was carried out for a series of Pb-based quaternary compounds ${\mathrm{PbBi}}_{2}{\mathrm{Te}}_{4\ensuremath{-}x}{\mathrm{Se}}_{x}$. For all values of $x$, these compounds are theoretically predicted to be topological insulators, possessing at high Se content a remarkably large band gap and a Dirac point isolated from bulk states. Using spin- and angle-resolved photoemission spectroscopy, it was shown that the ${\mathrm{PbBi}}_{2}{\mathrm{Te}}_{2}{\mathrm{Se}}_{2}$ and ${\mathrm{PbBi}}_{2}{\mathrm{Te}}_{1.4}{\mathrm{Se}}_{2.6}$ compounds are characterized by well-defined spin-polarized topological surface state in the bulk gap. To define the probable distribution of atoms over the atomic sites for these samples, we performed ab initio calculations in ordered and disordered configurations of the unit cell. We found that theoretical calculations better reproduce photoemission data when Te atoms are placed in the outermost layers of the septuple layer block.

In this work, we employed angle resolved photoemission spectroscopy (ARPES) to analyze the temperature dependent changes in the electronic structure of the first antiferromagnetic topological insulator MnBi2Te4 upon crossing the Néel temperature TN ≈ 25 K. We observed an exchange splitting of the bulk conduction band, which has a power law dependence on temperature (1−T/T0)2β with an onset temperature T0 well matching the measured bulk TN. We found a matching temperature evolution of the topological surface states integrated spectral weight in the vicinity of the Dirac point. Furthermore, we observed an additional quasi-2D state with Rashba-type splitting, which is also affected by the emerged magnetism and exhibits an opening of a gap, reminiscent of the effect of an out-of-plane magnetic field, below TN. All these findings point toward strong evidence of the interplay between emerged magnetism with bulk and topological surface states. The observed temperature-dependent effects in MnBi2Te4 may be used as an experimental fingerprint for the presence of magnetism and may guide the future analysis of ARPES spectra in magnetic topological insulators., The authors acknowledge support from the Saint Petersburg State University (Grant No. 51126047), the Russian Science Foundation (Grant No. 18-12-00062), and the Russian Foundation for Fundamental Investigations (No. 20-32-70179). The ARPES experiments were performed at HiSOR under Proposal Nos. 18BG026 and 18BU006. A. Kimura was financially supported by KAKENHI (Grant Nos. 17H06138, 17H06152, and 18H03683). Z. S. Aliev and M. B. Babanly acknowledge support from the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EIF/MQM/Elm-Tehsil-1-2016-1(26)-71/01/4-M-33). The support by Tomsk State University competitiveness improvement program (No. 8.1.01.2018) is gratefully acknowledged.

The non-volatile spin-orbit torque magnetic random access memory (SOT-MRAM) is a very attractive memory technology for near future computers because it has various advantages such as non-volatility, high density and scalability. In the present work we propose a model of a graphene recording device for the SOT-MRAM unit cell, consisting of a quasi-freestanding graphene intercalated with Au and an ultra-thin Pt layer sandwiched between graphene and a magnetic tunnel junction. As a result of using the claimed graphene recording memory element, a faster operation and lower energy consumption will be achieved under the recording information by reducing the electric current required to record. The efficiency of the graphene recording element was confirmed by the experimental results and the theoretical estimations.

A comparative study of the electronic and optical properties of Mn-Bi-Te layered compounds was carried out using spectroscopic ellipsometry (SE) over a photon energy range of 0.7-6.5 eV at room temperature and density functional theory (DFT)-based first-principle calculations within the general gradient approximation with Hubbard like correction (GGA+U) and allowance for a spin-orbital coupling. The total energies of the above compounds in ferromagnetic (FM) and antiferromagnetic (AFM) spin configurations are obtained by taking the long-range van der Waals interaction into account. The stability of the AFM state of MnBiTe and MnBiTe over the corresponding FM counterpart is disclosed. The SE-based and calculated dielectric functions are compared. It is shown that interband optical transitions in the accessed photon energy range mainly occur between Mn 3d + Te 5p states of the valence band and Bi 6p + Te 5p with a small admixture of Mn 3d states of the conduction band., We acknowledge the support by the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02), Russian Foundation for Basic Research (Grant No. 18-52-06009), the Basque Departamento de Educación, UPV/EHU (Grant No. IT-756-13), Spanish Ministerio de Economia y Competitividad (MINECO Grant No. FIS2016-75862-P), the Saint Petersburg State University grant for scientific investigations (Grant No.15.61.202.2015). M.M.O. acknowledges support by the Diputación Foral de Gipuzkoa (SAREA 2018 - RED 2018*, *Project No. 2018-CIEN-000025-01).

The electronic and spin structure of quantum-well and interface states, formed in the system, consisting of bilayer of Bi on 1 ML Ag/W(110) was investigated by angle- and spin- resolved photoelectron spectroscopy. It has been shown that interface states are formed in local surface-projected gap of W(110) and are characterized by spin polarization and spin-orbit splitting, corresponding to surface resonances with high density spin-polarized states near Fermi edge.

This paper reports on a study of the process of Al intercalation underneath a graphene monolayer formed on the Ni(111) surface by propylene cracking. Graphene formed on Ni(111) is known to be strongly coupled to the substrate; however, we have been able to show that Al intercalation underneath a graphene monolayer eventually results in blocking of this interaction and the formation of an electronic structure similar to that of quasi-freestanding graphene. As a result, the dispersion relation of the π states of graphene is linear at the К point of the Brillouin zone, with the Dirac point located in the region of the Fermi level. Thereat, an energy gap opens at the Fermi level near the K¯ point between the cones of occupied π and unoccupied π* states of graphene. There are no features in the spectra that would signal a partial filling of the π* states and clearly detectable charge transfer between the graphene and the intercalated Al. A detailed analysis of the process by which Al intercalates underneath the graphene monolayer revealed that intercalation of Al differs somewhat from that of other (for instance, noble) metals. The intercalated Al is observed to dissolve and subsequently, alloy with the Ni substrate. Only if the concentration of Al intercalated underneath the graphene is high enough, will it accumulate on the interface directly under the graphene monolayer and form, in the near-surface region, an alloy with a prevalent concentration of Al; the stage at which the strong binding of graphene to the Ni substrate becomes blocked.

In a recent article, we studied the electronic and spin structure of graphene on Pt(111) with intercalated Pb monolayer. By means of ARPES, we have shown that the Dirac cone of graphene is characterized by the gap between the π and π* states in this system. The spin texture of the π and π* states and its correspondence with the Kane and Mele model for graphene with spin−orbit gap have been unveiled by spinresolved ARPES. In the Comment on our paper, Dedkov and Voloshina claim that (1) the notation of the superstructure used in our work is incorrect, and (2) spin-resolved data treatment is inappropriate. In this Reply, we show that the superstructure notation is indeed correct. Moreover, the statistical analysis of the reported spin-resolved ARPES data and new experimental data with better statistics support the main conclusion of our article., The work was partially supported by grant of Saint Petersburg State University for scientific investigations (No. 15.61.202.2015) and DFG - SPbU grant No. 11.65.42.2017. We acknowledge support by the University of the Basque Country (Grant Nos. GIC07IT36607 and IT-756-13), the Spanish Ministry of Science and Innovation (Grant Nos. FIS2013-48286-C02-02-P, FIS2013-48286-C02-01-P, and FIS2016-75862-P), and Tomsk State University competitiveness improvement programme (Project No. 8.1.01.2017). The part of photoemission measurements was supported by Russian Science Foundation (Project No. 17-12-01047). The authors acknowledge support from the Russian−German laboratory at BESSY II and the “German−Russian Interdisciplinary Science Center”(G-RISC) program.

One of the most promising platforms for spintronics and topological quantum computation is the two-dimensional electron gas (2DEG) with strong spin-orbit interaction and out-of-plane ferromagnetism. In proximity to an s-wave superconductor, such 2DEG may be driven into a topologically non-Trivial superconducting phase, predicted to support zero-energy Majorana fermion modes. Using angle-resolved photoemission spectroscopy and ab initio calculations, we study the 2DEG at the surface of the vanadium-doped polar semiconductor with a giant Rashba-Type splitting, BiTeI. We show that the vanadium-induced magnetization in the 2DEG breaks time-reversal symmetry, lifting Kramers degeneracy of the Rashba-split surface state at the Brillouin zone center via formation of a huge gap of about 90 meV. As a result, the constant energy contour inside the gap consists of only one circle with spin-momentum locking. These findings reveal a great potential of the magnetically-doped semiconductors with a giant Rashba-Type splitting for realization of novel states of matter., The work was partially supported by grant of Saint Petersburg State University for scientific investigations (N. 15.61.202.2015). This study was supported by the Russian Science Foundation (project N. 17-12-01047, in part of crystal growth, structural characterization and ARPES measurements (Figs 1, 2)). The funding by the University of the Basque Country (Grant Nos GIC07IT36607 and IT-756-13), the Spanish Ministry of Science and Innovation (Grant Nos FIS2013-48286-C02-02-P, FIS2013-48286-C02-01-P, and FIS2016-75862-P) and Tomsk State University Academic D.I. Mendeleev Fund Program in 2015 (research grant N 8.1.05.2015) are also gratefully acknowledged. The authors also acknowledge support from the Russian-German laboratory at BESSY II, the “German-Russian Interdisciplinary Science Center”(G-RISC) program and the Impuls- und Vernetzungsfonds der Helmholtz-Gemeinschaft (Grant No. HRJRG-408).

Two-and three-dimensional topological insulators are the key materials for the future nanoelectronic and spintronic devices and quantum computers. By means of angle-and spin-resolved photoemission spectroscopy we study the electronic and spin structure of the Bi-bilayer/3D topological insulator in quantum tunneling regime formed under the short annealing of BiTeSe Owing to the temperature-induced restructuring of the topological insulator's surface quintuple layers, the hole-like spin-split Bi-bilayer bands and the parabolic electronic-like state are observed instead of the Dirac cone. Scanning Tunneling Microscopy and X-ray Photoemission Spectroscopy measurements reveal the appearance of the Bi terraces at the surface under the annealing. The experimental results are supported by density functional theory calculations, predicting the spin-polarized Bi-bilayer bands interacting with the quintuple-layers-derived states. Such an easily formed heterostructure promises exciting applications in spin transport devices and low-energy electronics., The work was partially supported by grant of Saint Petersburg State University for scientific investigations (No 15.61.202.2015). We acknowledge the financial support of the University of Basque Country UPV/EHU (Grant No. GIC07-IT-756-13), the Departamento de Educación del Gobierno Vasco and the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-01), the Spanish Ministry of Economy and Competitiveness MINECO (Grant No. FIS2013-48286-C2-1-P) and the Tomsk State University Competitiveness Improvement Program.

The effect of intercalation of Bi atoms and the joint intercalation of atoms of Bi and noble metals (Au, Cu) on the spin and electron structure of graphene formed on Ni(111) is investigated by angle and spin-resolved PES. It is shown that the spin-orbit splitting of π states of graphene of 20–30 meV is observed for the joint intercalation of Bi and Au.

Changes in the electronic structure of the valence band and the corresponding dispersion dependences of the electron states of graphene synthesized by a cracking catalytic reaction of propylene at the surface of Ni(111) thin layers and the subsequent intercalation of Au atoms underneath the formed monolayer of graphene have been measured and analyzed using angle-resolved photoelectron spectroscopy. It is shown that this technique of graphene synthesis causes the formation of a monolayer graphene cover over large areas with features of the electronic structure typical for a quasifree graphene: a linear dispersion of graphene π states in the region of the point of the Brillouin zone with the Dirac point localization near the Fermi level. It was established that contact between the graphene monolayer and the intercalated Au layer additionally causes a substrate-induced spin-orbital splitting of graphene π states, which also occurs in the region of dispersion-dependence linearity.

Angle-resolved photoelectron spectroscopy study of the electronic structure of pentacene monolayer film on Ni(110) surface and its comparison with the electronic structure of graphene are presented. It is shown that pentacene molecules adsorbed on the Ni(110) surface are aligned in one direction. The electronic structure of the pentacene monolayer in the direction along molecules is closely related to the graphene electronic structure showing pronounced dispersion due to intermolecular interactions, while in the perpendicular direction it has a nondispersing molecular spectrum.