Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with... more Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with n<4, where index n is the number of quintuple Te-BiTe -BiTe building blocks inserted between the neighboring septuple Te-BiTe -Mn-Te-BiTe building blocks, the structure of the members with n=4, 5 and 6 was studied using X-ray powder diffraction. The unit cell parameters and atomic positions were calculated. The obtained and available structural data were summarized to show that the crystal structure of all members of MnBi2Te4 n(Bi2Te3) follows the cubic close packing principle, independently of the space group of the given member. Confocal Raman spectroscopy was then applied. Comparative analysis of the number, frequency, symmetry, and broadening of the vibration modes responsible for the lines in the Raman spectra of the systems with n=1,.. . ,6, as well as MnBi2Te4 (n=0) and Bi2Te3 (n=) has shown that lattice dynamics of MnBi2Te4 n(Bi2Te3) with n>0 overwhelmingly dominates by the cooperative atomic displacements in the quintuple building blocks. I.
Phase equilibria in the quasi-ternary system Bi2S3–Bi2Te3–BiI3 were studied by differential therm... more Phase equilibria in the quasi-ternary system Bi2S3–Bi2Te3–BiI3 were studied by differential thermal analysis, X-ray powder diffraction analysis, and scanning electron microscopy. The isothermal sections at 300, 750, 800, and 850 K were constructed, and so were some polythermal sections and a projection of the liquidus surface. The primary crystallization fields and homogeneity regions of phases, and the types and coordinates of in- and monovariant equilibria were determined. It was shown that the system is characterized by the formation of limited regions of solid solutions based on bismuth sulfide and telluride, and also ternary compounds Bi2Te2S, BiSI, and BiTeI.
The phase eqilibria in the Pb-BiTe -Se quaternary system along the PbBi 2 Te 4-PbBi 2 Se 4 iso... more The phase eqilibria in the Pb-BiTe -Se quaternary system along the PbBi 2 Te 4-PbBi 2 Se 4 isopleth section was investigated experimentally using differential thermal analysis and X-ray diffraction analyses of the equilibrated alloys. It was shown that the system is non-quasi-binary one and featured by the formation of the tetradymite-type solid solutions based on the PbBi 2 Te 4 in the wide range of concentration. The system has a more complex phase equilibria scheme that comes from its host reciprocal PbTe-PbSe-Bi 2 Se 3-Bi 2 Te 3 system. One can see that, in order to reveal the phase equilibria scheme and understand the crystallization scheme, reactions types etc., the thorough investigation of the entire pointed reciprocal PbTe-PbSe-Bi 2 Se 3-Bi 2 Te 3 system is very important.
⎯The literature data on topological insulators (TIs) based on metal chalcogenides, which constitu... more ⎯The literature data on topological insulators (TIs) based on metal chalcogenides, which constitute a new unique class of functional materials, are systematized here in the context of physicochemical analysis and crystal chemistry. An accent is on the phase diagrams of relevant systems and the crystal structures of the main TI types. We show that, for search and design of new phases having TI properties, it will be expedient to revise earlier constructed phase diagrams for some systems, especially B V-Se(Te) and A IV-B V-Te (A IV = Ge, Sn, Pb; B V = Sb, Bi) systems, using new approaches to studies of phase equilibria. There is also a need for systematic studies of complex systems involving binary and ternary TIs.
Topological insulators in which the Fermi level is in the bulk gap and intersects only a topologi... more Topological insulators in which the Fermi level is in the bulk gap and intersects only a topological surface state (the Dirac cone) are of special interest in the current research. In the last decades, a fine-tuning of the chemical composition of topological insulators has been carefully explored in order to control the Fermi level position with respect to the Dirac surface state. Taking the SnBi 2 Te 4 crystal as a case study, we provide a characterization of its electronic structure by means of angle-resolved photoemission spectroscopy and first-principles calculations. We show that, going away from the Brillouin zone center, bulk band states energetically overlap with the Dirac cone at the Fermi level, thus providing an unwanted as well as hidden contribution to the transport properties of the material. In addition, the comparison between experimental results of the band structure with state-of-the-art simulations, implemented taking into account the number of defects, leads to useful insights on the existing limits in the description of this material.
By using Differential Thermal Analysis (DTA) and Powder X-ray Diffraction (PXRD) techniques, the ... more By using Differential Thermal Analysis (DTA) and Powder X-ray Diffraction (PXRD) techniques, the phase diagram of the MnTe-Sb2Te3 system has been constructed for the first time in the entire composition range. The system features two ternary layered van der Waals (vdW) compounds. Apart from known MnSb2Te4, novel MnSb4Te7 which a structural analogous of the known MnBi4Te7 was found in the system. Crystal structure parameters of both compounds were determined by Rietveld refinement using the fundamental parameter approach. Both compounds were found to decompose via peritectic reactions and possess significant homogeneity ranges. The title system is also characterized by the existence of the wide solid solution field based on the starting Sb2Te3. The present results would be useful for the bulk single crystal growth of both compounds from the liquid phase via the determination of primary crystallization areas.
Topological surface states usually emerge at the boundary between a topological and a conventiona... more Topological surface states usually emerge at the boundary between a topological and a conventional insulator. Their precise physical character and spatial localization depend on the complex interplay between the chemical, structural and electronic properties of the two insulators in contact. Using a lattice-matched heterointerface of single and double bilayers of β-antimonene and bismuth selenide, we perform a comprehensive experimental and theoretical study of the chiral surface states by means of microscopy and spectroscopic measurements complemented by first-principles calculations. We demonstrate that, although β-antimonene is a trivial insulator in its free-standing form, it inherits the unique symmetry-protected spin texture from the substrate via a proximity effect that induces outward migration of the topological state. This “topologization” of β-antimonene is found to be driven by the hybridization of the bands from either side of the interface.
By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional... more By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations, the electronic band structure of the topological insulator PbBi 4 Te 4 Se 3 for both five-layer and seven-layer surface terminations is investigated. The measured and calculated band structure features are in good agreement and indicate two well-resolved topological surface states with distinct spatial localizations within bulk band gap of about 0.3 eV.
We derive analytical expressions for the free energy of mixing of (YbTe)х(PbTe)1–х and (YbTe)х(Sn... more We derive analytical expressions for the free energy of mixing of (YbTe)х(PbTe)1–х and (YbTe)х(SnTe)1–х solid solutions in the temperature range 600–1095 K and accurately determine the location of their phase boundaries. Т–х–у relations for the solidus surface and the spinodal decomposition of solid solutions in the pseudoternary system YbTe–PbTe–SnTe are found.
PbTe system have been studied using differential thermal analysis, X-ray diffraction, scanning el... more PbTe system have been studied using differential thermal analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on YbTe concentration cells. We have mapped out a number of vertical sections, the 400-K isothermal section of the YbTe-SnTe-PbTe phase diagram, and projections of its liquidus and solidus surfaces. The results demonstrate that the system is characterized by the formation of a continuous series of high-temperature solid solutions with a cubic structure (NaCl type), which undergo decomposition below ~1050 K. At room temperature, the YbTe solubility in the Sn 1-x Pb x Te solid solution system is ~33-35 mol %, whereas the extent of the YbTe-based solid solution series does not exceed 3 mol %.
We have investigated plasmonic excitations at the surface of Bi 2 Se 3 ð0001Þ via high-resolution... more We have investigated plasmonic excitations at the surface of Bi 2 Se 3 ð0001Þ via high-resolution electron energy loss spectroscopy. For low parallel momentum transfer q ∥ , the loss spectrum shows a distinctive feature peaked at 104 meV. This mode varies weakly with q ∥. The behavior of its intensity as a function of primary energy and scattering angle indicates that it is a surface plasmon. At larger momenta (q ∥ ∼ 0.04 Å −1), an additional peak, attributed to the Dirac plasmon, becomes clearly defined in the loss spectrum. Momentum-resolved loss spectra provide evidence of the mutual interaction between the surface plasmon and the Dirac plasmon of Bi 2 Se 3. The proposed theoretical model accounting for the coexistence of three-dimensional doping electrons and two-dimensional Dirac fermions accurately represents the experimental observations. The results reveal novel routes for engineering plasmonic devices based on topological insulators.
Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with... more Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with n<4, where index n is the number of quintuple Te-BiTe -BiTe building blocks inserted between the neighboring septuple Te-BiTe -Mn-Te-BiTe building blocks, the structure of the members with n=4, 5 and 6 was studied using X-ray powder diffraction. The unit cell parameters and atomic positions were calculated. The obtained and available structural data were summarized to show that the crystal structure of all members of MnBi2Te4 n(Bi2Te3) follows the cubic close packing principle, independently of the space group of the given member. Confocal Raman spectroscopy was then applied. Comparative analysis of the number, frequency, symmetry, and broadening of the vibration modes responsible for the lines in the Raman spectra of the systems with n=1,.. . ,6, as well as MnBi2Te4 (n=0) and Bi2Te3 (n=) has shown that lattice dynamics of MnBi2Te4 n(Bi2Te3) with n>0 overwhelmingly dominates by the cooperative atomic displacements in the quintuple building blocks. I.
Phase equilibria in the quasi-ternary system Bi2S3–Bi2Te3–BiI3 were studied by differential therm... more Phase equilibria in the quasi-ternary system Bi2S3–Bi2Te3–BiI3 were studied by differential thermal analysis, X-ray powder diffraction analysis, and scanning electron microscopy. The isothermal sections at 300, 750, 800, and 850 K were constructed, and so were some polythermal sections and a projection of the liquidus surface. The primary crystallization fields and homogeneity regions of phases, and the types and coordinates of in- and monovariant equilibria were determined. It was shown that the system is characterized by the formation of limited regions of solid solutions based on bismuth sulfide and telluride, and also ternary compounds Bi2Te2S, BiSI, and BiTeI.
The phase eqilibria in the Pb-BiTe -Se quaternary system along the PbBi 2 Te 4-PbBi 2 Se 4 iso... more The phase eqilibria in the Pb-BiTe -Se quaternary system along the PbBi 2 Te 4-PbBi 2 Se 4 isopleth section was investigated experimentally using differential thermal analysis and X-ray diffraction analyses of the equilibrated alloys. It was shown that the system is non-quasi-binary one and featured by the formation of the tetradymite-type solid solutions based on the PbBi 2 Te 4 in the wide range of concentration. The system has a more complex phase equilibria scheme that comes from its host reciprocal PbTe-PbSe-Bi 2 Se 3-Bi 2 Te 3 system. One can see that, in order to reveal the phase equilibria scheme and understand the crystallization scheme, reactions types etc., the thorough investigation of the entire pointed reciprocal PbTe-PbSe-Bi 2 Se 3-Bi 2 Te 3 system is very important.
⎯The literature data on topological insulators (TIs) based on metal chalcogenides, which constitu... more ⎯The literature data on topological insulators (TIs) based on metal chalcogenides, which constitute a new unique class of functional materials, are systematized here in the context of physicochemical analysis and crystal chemistry. An accent is on the phase diagrams of relevant systems and the crystal structures of the main TI types. We show that, for search and design of new phases having TI properties, it will be expedient to revise earlier constructed phase diagrams for some systems, especially B V-Se(Te) and A IV-B V-Te (A IV = Ge, Sn, Pb; B V = Sb, Bi) systems, using new approaches to studies of phase equilibria. There is also a need for systematic studies of complex systems involving binary and ternary TIs.
Topological insulators in which the Fermi level is in the bulk gap and intersects only a topologi... more Topological insulators in which the Fermi level is in the bulk gap and intersects only a topological surface state (the Dirac cone) are of special interest in the current research. In the last decades, a fine-tuning of the chemical composition of topological insulators has been carefully explored in order to control the Fermi level position with respect to the Dirac surface state. Taking the SnBi 2 Te 4 crystal as a case study, we provide a characterization of its electronic structure by means of angle-resolved photoemission spectroscopy and first-principles calculations. We show that, going away from the Brillouin zone center, bulk band states energetically overlap with the Dirac cone at the Fermi level, thus providing an unwanted as well as hidden contribution to the transport properties of the material. In addition, the comparison between experimental results of the band structure with state-of-the-art simulations, implemented taking into account the number of defects, leads to useful insights on the existing limits in the description of this material.
By using Differential Thermal Analysis (DTA) and Powder X-ray Diffraction (PXRD) techniques, the ... more By using Differential Thermal Analysis (DTA) and Powder X-ray Diffraction (PXRD) techniques, the phase diagram of the MnTe-Sb2Te3 system has been constructed for the first time in the entire composition range. The system features two ternary layered van der Waals (vdW) compounds. Apart from known MnSb2Te4, novel MnSb4Te7 which a structural analogous of the known MnBi4Te7 was found in the system. Crystal structure parameters of both compounds were determined by Rietveld refinement using the fundamental parameter approach. Both compounds were found to decompose via peritectic reactions and possess significant homogeneity ranges. The title system is also characterized by the existence of the wide solid solution field based on the starting Sb2Te3. The present results would be useful for the bulk single crystal growth of both compounds from the liquid phase via the determination of primary crystallization areas.
Topological surface states usually emerge at the boundary between a topological and a conventiona... more Topological surface states usually emerge at the boundary between a topological and a conventional insulator. Their precise physical character and spatial localization depend on the complex interplay between the chemical, structural and electronic properties of the two insulators in contact. Using a lattice-matched heterointerface of single and double bilayers of β-antimonene and bismuth selenide, we perform a comprehensive experimental and theoretical study of the chiral surface states by means of microscopy and spectroscopic measurements complemented by first-principles calculations. We demonstrate that, although β-antimonene is a trivial insulator in its free-standing form, it inherits the unique symmetry-protected spin texture from the substrate via a proximity effect that induces outward migration of the topological state. This “topologization” of β-antimonene is found to be driven by the hybridization of the bands from either side of the interface.
By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional... more By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations, the electronic band structure of the topological insulator PbBi 4 Te 4 Se 3 for both five-layer and seven-layer surface terminations is investigated. The measured and calculated band structure features are in good agreement and indicate two well-resolved topological surface states with distinct spatial localizations within bulk band gap of about 0.3 eV.
We derive analytical expressions for the free energy of mixing of (YbTe)х(PbTe)1–х and (YbTe)х(Sn... more We derive analytical expressions for the free energy of mixing of (YbTe)х(PbTe)1–х and (YbTe)х(SnTe)1–х solid solutions in the temperature range 600–1095 K and accurately determine the location of their phase boundaries. Т–х–у relations for the solidus surface and the spinodal decomposition of solid solutions in the pseudoternary system YbTe–PbTe–SnTe are found.
PbTe system have been studied using differential thermal analysis, X-ray diffraction, scanning el... more PbTe system have been studied using differential thermal analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on YbTe concentration cells. We have mapped out a number of vertical sections, the 400-K isothermal section of the YbTe-SnTe-PbTe phase diagram, and projections of its liquidus and solidus surfaces. The results demonstrate that the system is characterized by the formation of a continuous series of high-temperature solid solutions with a cubic structure (NaCl type), which undergo decomposition below ~1050 K. At room temperature, the YbTe solubility in the Sn 1-x Pb x Te solid solution system is ~33-35 mol %, whereas the extent of the YbTe-based solid solution series does not exceed 3 mol %.
We have investigated plasmonic excitations at the surface of Bi 2 Se 3 ð0001Þ via high-resolution... more We have investigated plasmonic excitations at the surface of Bi 2 Se 3 ð0001Þ via high-resolution electron energy loss spectroscopy. For low parallel momentum transfer q ∥ , the loss spectrum shows a distinctive feature peaked at 104 meV. This mode varies weakly with q ∥. The behavior of its intensity as a function of primary energy and scattering angle indicates that it is a surface plasmon. At larger momenta (q ∥ ∼ 0.04 Å −1), an additional peak, attributed to the Dirac plasmon, becomes clearly defined in the loss spectrum. Momentum-resolved loss spectra provide evidence of the mutual interaction between the surface plasmon and the Dirac plasmon of Bi 2 Se 3. The proposed theoretical model accounting for the coexistence of three-dimensional doping electrons and two-dimensional Dirac fermions accurately represents the experimental observations. The results reveal novel routes for engineering plasmonic devices based on topological insulators.
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Papers by Ziya Aliev