arXiv subjects

I. R. Shein

Publications and source records attributed to I. R. Shein.

At least 19 recordsLinked to original sources

arXiv2024

Pressurized phase transition cascade in BaMn$_2$P$_2$ and BaMn$_2$As$_2$

The structural analogue of iron-based superconductors the BaMn$_2$P$_2$ and BaMn$_2$As$_2$ compounds under hydrostatic pressure upto 140 GPa were studied within the framework of DFT+U. The transition from an antiferromagnetic (AFM) insulator to an antiferromagnetic metal is observed under pressure of 6.4 GPa for BaMn$_2$P$_2$ and 8.3 GPa for BaMn$_2$As$_2$. This second order phase transition to the AFM metallic state provides an appropriate normal state for possible superconductivity in these materials. Moreover, a further increase in pressure leads to a series of first order magnetostructural phase transitions between different antiferromagnetic phases, then to a ferromagnetic metal and finally to a nonmagnetic metal. In case of doping these compounds could potentially be a superconductors under pressure (above 6-8 GPa) with critical temperature growing under pressure.

cond-mat.supr-con↗

arXiv2024

Exchange Splitting Mechanism of Negative Magnetoresistance in Layered Antiferromagnetic Semimetals

Layered topologically non-trivial and trivial semimetals with AFM-type ordering of magnetic sublattice are known to exhibit a negative magnetoresistance that is well correlated with AFM magnetization changes in a magnetic field. This effect is reported in several experimental studies with EuFe$_2$As$_2$, EuSn$_2$As$_2$, EuSn$_2$P$_2$, etc., where the resistance decreases quadratically with field by about $δρ/ρ\sim 4-6\%$ up to the spin-polarization field. Despite the fact that this effect is well documented experimentally, its theoretical explanation is missing up to date. In this paper we propose a novel theoretical mechanism describing the observed magnetoresistance that does not imply either topological origin of the materials, surface roughness, their potential defect structure, or electron-magnon scattering. We believe, the proposed intrinsic mechanism of magnetoresistance is applicable to a wide class of the layered AFM- ordered semimetals. The theoretically calculated magnetoresistance is qualitatively consistent with experimental data for crystals of various composition.

cond-mat.mes-hall↗

arXiv2019

Structural, electronic properties and the features of chemical bonding in layered 1111-oxyarsenides LaRhAsO and LaIrAsO: ab initio modeling

The comparative study of structural, electronic properties, topology of the Fermi surface, and the features of chemical bonding in layered 1111-oxyarsenides LaRhAsO and LaIrAsO has been performed based on the results of ab initio modeling of their electronic structure. It was established that only weak sensitivity with respect both to electron and hole doping is expected for LaIrAsO being non-magnetic metal, however, the Rh-containing compound should be characterized with weak band magnetism, and the hole doping is expected to be able to move its ground state away from the boundary of magnetic instability. The mentioned feature allows to consider LaRhAsO oxyarsenide as a possible "electron analogue" of LaFeAsO compound being the initial phase for the layered FeAs-superconductors.

cond-mat.mtrl-sci↗

arXiv2017

Electronic structure for new layered high-temperature superconductors CaAFe4As4 (A=K, Rb, Cs): FLAPW-GGA calculations

Recently, new FeAs based high-temperature superconductors CaAFe4As4 (A=K, Rb, Cs) with a layered tetragonal crystal structure were synthesized (TC ~ 30 K). In this Letter, we report for the first time the band structures, Fermi surface topology, total and partial densities of electronic states and interatomic interactions for CaAFe4As4 as estimated by means of the first-principles FLAPW-GGA calculations. The interatomic bonding picture can be represented as a highly anisotropic mixture of metallic, covalent, and ionic contributions, which are realized inside Fe4As4 layered blocks and between these blocks and Ca, A atomic sheets. The Fermi surfaces of these systems have a multisheet character and are compiled of a large number of cylinders at the edges and in the central part of the Brillouin zone. It is established that the high-temperature superconductivity in CaAFe4As4 compounds as in other related systems correlates well with such structure parameters as bond angles and anion height.

cond-mat.supr-con↗

arXiv2013

Electronic band structure, Fermi surface, structural and elastic properties of two polymorphs of MgFeSeO as possible new superconducting systems

By means of DFT-based first-principles calculations, we examine two polymorphs of the newly synthesized 1111-like MgFeSeO as possible new superconducting systems. We have found that the polymorph with blocks [MgO], where Mg atoms are placed in the centers of O4 tetrahedra, is dynamically unstable - unlike the ZrCuSiAs-type polymorph with oxygen atoms placed in the centers of Mg4 tetrahedra. The characterization of this material covers the structural, elastic properties, electronic band structure, density of electronic states, and Fermi surface. Our calculations suggest that a high critical temperature for MgFeSeO may be achieved as a result of electron or hole doping through ion substitutions or through creation of lattice vacancies.

cond-mat.supr-con↗

arXiv2012

Electronic band structure and Fermi surface for new layered superconductor LaO0.5F0.5BiS2 in comparison with parent phase LaOBiS2 from first principles

By means of first-principles calculations? we have probed the peculiarities of the elecrtonic band structure and Fermi surface for the recently discovered layered superconductor LaO0.5F0.5BiSi2 in comparison with the parent phase LaOBiO2. The electronic factors prpmoting the transition of LaOBiS2 upon fluorine doping to superconducting state: inter-layer charge transfer, the evolution of the Fermi surface, and the dependence of the near-Fermi densities of states on x for LaO1-xFxBiS2 are evaluated and discussed in comparison with the available experiments.

cond-mat.supr-con↗

arXiv2012

Ab initio study of the elastic and electronic properties of tetragonal Th2NiC2

This work reports on the elastic and electronic properties of the newly discovered superconductor Th2NiC2 (A .Machado, et al., Supercond. Sci. Technol. 25 (2012) 045010) as obtained within ab initio calculations. We found that Th2NiC2 is mechanically stable and it will behave as a ductile material exhibiting enhanced elastic anisotropy in shear and a rather low hardness Our data reveal that for Th2NiC2 the Fermi level is located in a deep DOS minimum and the experimentally observed increase in TC in the sequence Th2NiC2 -> Th1.8Sc0.2NiC2 may be explained by the growth of N(EF). We also speculate that (i) an increase in the hole concentration will promote exchange splitting of Ni 3d bands, therefore the hole-doped Th2NiC2 should have a certain concentration border, where a phase transition from the superconducting to the magnetic state will be expected, and (ii) an increase in N(EF) (and, probably, in TC) for Th2NiC2-based materials may be also achieved by an alternative way: by electron doping - for example, by partial substitution of V for Th or Cu for Ni, as well as by partial substitution of N for C with the formation of Th-Ni carbonitrides like Th2NiC2-xNx.

cond-mat.supr-con↗

arXiv2012

Electronic band structure, Fermi surface and effect of spin-orbit coupling for tetragonal low-temperature superconductor Bi2Pd from first principles

We have examined theoretically the electronic band structure and Fermi surface of tetragonal low-temperature superconductor Bi2Pd. Our main results are that (i) the Pd 4d and Bi 6p states determine the main peculiarities of the multiple-sheets FS topology, thus for this material the complicated superconducting gap structure with different energy gaps on different FS sheets should be assumed; (ii) the effect of the spin-orbit coupling is of minor importance for the distributions of the near-Fermi electronic states; and (iii) this phase adopts 3D-like type owing to the directional bonds between the adjacent atomic sheets.

cond-mat.supr-con↗

arXiv2012

Electronic, magnetic properties and correlation effects in the layered quaternary iron oxyselenide Na2Fe2Se2O from first principles

By means of the first-principle calculations, we have investigated electronic, magnetic properties and correlation effects for the newly discovered layered oxyselenide Na2Fe2Se2O. Our results reveal that the electron correlations in the Fe 3d bands promote a transition of Na2Fe2Se2O from magnetic metallic or half-metallic states to the antiferromagnetic Mott-insulating state. In addition, the bonding picture in Na2Fe2Se2O is described as an anisotropic mixture of ionic and covalent contributions.

cond-mat.mtrl-sci↗

arXiv2011

Ab initio probing of the electronic band structure and Fermi surface of fluorine-doped WO3 as a novel low-TC superconductor

First-principles calculations were performed to investigate the electronic structure and the Fermi surface of the newly discovered low-temperature superconductor: fluorine-doped WO3. We find that F doping provides the transition of the insulating tungsten trioxide into a metallic-like phase WO3-xFx, where the near-Fermi states are formed mainly from W 5d with admixture of O 2p orbitals. The cooperative effect of fluorine additives in WO3 consists in change of electronic concentration as well as the lattice constant. At probing their influence on the near-Fermi states separately, the dominant role of the electronic factor for the transition of tungsten oxyfluoride into superconducting state was established. The volume of the Fermi surface gradually increases with the increase of the doping. In the sequence WO3 \rightarrow WO2.5F0.5 the effective atomic charges of W and O ions decrease, but much less, than it is predicted within the idealized ionic model - owing to presence of the covalent interactions W-O and W-F.

cond-mat.supr-con↗

arXiv2011

Electronic structure and chemical bonding in novel tetragonal phase Ca10(Pt4As8)(Fe2As2)5 as a parent material for the new family of high-TC iron-pnictide superconductors

By means of first-principles calculations, the electronic structure and chemical bonding for the recently discovered tetragonal (s.g. P4/n; # 85) superconducting (Tc ~ 25K) phase Ca10(Pt4As8)(Fe2As2)5 have been examined in details, and the optimized structural parameters, electronic bands, densities of states, and inter-atomic bonding picture were evaluated and analyzed in comparison with related layered iron-based superconducting materials. We have shown that (i) Ca10(Pt4As8)(Fe2As2)5 is metallic-like, and the electronic bands in the window around the Fermi level are formed mainly by the Fe 3d states of (Fe2As2)5 blocks; (ii) the (Pt4As8) blocks will behave as semi-metals with very low densities of states at the Fermi level; (iii) the near-Fermi bands adopt a "mixed" character: simultaneously with quasi-flat bands, a series of high-dispersive bands which intersect the Fermi level was found; (iv) the of chemical bonding in Ca10(Pt4As8)(Fe2As2)5 is very complicated and includes an anisotropic mixture of covalent, metallic, and ionic inter-atomic and inter-block interactions.

cond-mat.supr-con↗

arXiv2011

Electronic band structure, Fermi surface, and elastic properties of new 4.2K superconductor SrPtAs from first-principles calculations

The hexagonal phase SrPtAs (s.g. P6/mmm; #194) with a honeycomb lattice structure very recently was declared as a new low-temperature (TC ~ 4.2K) superconductor. Here by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt2As2.

cond-mat.supr-con↗

arXiv2011

Electronic band structure and inter-atomic bonding in layered 1111-like Th-based pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO from first principles calculations

First-principles FLAPW-GGA band structure calculations were employed to examine the structural, electronic properties and the chemical bonding picture for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be viewed as "intermediate" systems between two main isostructural groups of superconducting and semiconducting 1111 phases. The Th 5f states participate actively in the formation of valence bands and the Th 5f states for ThMPnO phases are itinerant and partially occupied. We found also that the bonding picture in ThMPnO phases can be classified as a high-anisotropic mixture of ionic and covalent contributions: inside [Th2O2] and [M2Pn2] blocks, mixed covalent-ionic bonds take place, whereas between the adjacent [Th2O2]/[M2Pn2] blocks, ionic bonds emerge owing to [Th2O2] \to [M2Pn2] charge transfer.

cond-mat.mtrl-sci↗

arXiv2011

Structural, electronic properties and Fermi surface of ThCr2Si2-type tetragonal KFe2S2, KFe2Se2, and KFe2Te2 phases as parent systems of new ternary iron-chalcogenide superconductors

First principles FLAPW-GGA method was used for the comparative study of the structural and electronic properties of three related tetragonal ThCr2Si2-type phases KFe2Ch2, where Ch are S, Se, and Te. The main trends in electronic bands, densities of states and Fermi surfaces for AFe2Ch2 are analyzed in relation to their structural parameters. We found that at the anion replacements (S<->Se<->Te) any critical changes in electronic structure of KFe2Ch2 phases are absent. On the other hand, our analysis of structural and electronic parameters for hypothetical KFe2Te2 allows to assume that this system may be proposed as perspective parent phase for search of new iron-chalcogenide superconducting materials.

cond-mat.supr-con↗

arXiv2011

Elastic properties and inter-atomic bonding in new superconductor KFe2Se2 from first principles calculations

Very recently (November, 2010, PRB, 82, 180520R) the first 122-like ternary superconductor KxFe2Se2 with enhanced TC ~ 31K has been discovered. This finding has stimulated much activity in search of related materials and triggered the intense studies of their properties. Indeed already in 2010-2011 the superconductivity (TC ~ 27-33K) was also found in the series of new synthesized 122 phases such as CsxFe2Se2, RbxFe2Se2, (TlK)xFeySe2 etc. which have formed today the new family of superconducting iron-based materials without toxic As. Here, using the ab initio FLAPW-GGA method we have predicted for the first time the elastic properties for KFe2Se2 and discussed their interplay with inter-atomic bonding for this system. Our data reveal that the examined phase is relatively soft material. In addition, this system is mechanically stable, adopts considerable elastic anisotropy, and demonstrates brittleness. These conclusions agree with the bonding picture for KFe2Se2, where the inter-atomic bonding is highly anisotropic and includes ionic, covalent and metallic contributions.

cond-mat.supr-con↗

arXiv2011

Electronic band structure, Fermi surface and elastic properties of polymorphs of new 5.2K iron-free superconductor SrPt2As2 from first principles calculations

By means of the first-principles calculations, we have studied in details the structural, elastic and electronic properties of the new tetragonal CaBe2Ge2-type 5.2K superconductor SrPt2As2 in comparison with two hypothetical SrPt2As2 polymorphs with ThCr2Si2-type structures which differ by atomic configurations of [Pt2As2] (or [Pt2As2]) blocks. We have found that CaBe2Ge2-type SrPt2As2 is a quite unique system with complicated 2D-3D character of near-Fermi bands, and the "intermediate" type of the Fermi surface, which consists of electronic pockets having cylinder-like (2D) topology (typical for 122 FeAs phases) together with 3D-like electronic and hole pockets, which are characteristic for ThCr2Si2-like iron-free low-Tc superconductors. Our analysis reveals that against ThCr2Si2-like 122 phases, the other features for CaBe2Ge2-like SrPt2As2 are: (1). The essential differences of contributions of states from [Pt2As2] and [Pt2As2] blocks into near-Fermi region when the conduction is expected to be anisotropic and happening mainly in [Pt2As2] blocks; (2). The formation of the 3D system of strong covalent Pt-As bonds (inside and between of [Pt2As2]/[As2Pt2] blocks) which is responsible for enhanced stability of this polymorph, and (3). the essential charge anisotropy between the adjacent [Pt2As2] and [As2Pt2] blocks. We have predicted also that CaBe2Ge2-like SrPt2As2 is mechanically stable, relatively soft material with high compressibility and will behave in a ductile manner. On the contrary the ThCr2Si2-type SrPt2As2 polymorphs which contain only [Pt2As2] or [As2Pt2] blocks, are less stable, their Fermi surfaces adopt a multi-sheet three-dimensional type - similar to ThCr2Si2-like iron-free 122 phases, and these polymorphs will be ductile materials with high elastic anisotropy.

cond-mat.supr-con↗

arXiv2010

Electronic structure and Fermi surface of new K intercalated iron selenide superconductor KxFe2Se2

Using the ab initio FLAPW-GGA method we examine the electronic band structure, densities of states, and the Fermi surface topology for a very recently synthesized ThCr2Si2-type potassium intercalated iron selenide superconductor KxFe2Se2. We found that the electronic state of the stoichiometric KFe2Se2 is far from that of the isostructural iron pnictide superconductors. Thus the main factor responsible for experimentally observed superconductivity for this material is the deficiency of potassium, i.e. the hole doping effect. On the other hand, based on the results obtained, we conclude that the tuning of the electronic system of the new KxFe2Se2 superconductor in the presence of K vacancies is achieved by joint effect owing to structural relaxations and hole doping, where the structural factor is responsible for the modification of the band topology, whereas the doping level determines their filling.

cond-mat.supr-con↗

arXiv2010

Magnetic and electronic properties of nitrogen-doped lanthanum sesquioxide La2O3 as predicted from first principles

Using the ab initio FLAPW-GGA method we examine the electronic and magnetic properties of nitrogen-doped non-magnetic sesquioxide La2O3 emphasizing the role of doping sites in the occurrence of d0-magnetism. We predict the magnetization of La2O3 induced by nitrogen impurity in both octahedral and tetrahedral sites of the oxygen sublattice. The most interesting results are that (i) the total magnetic moments (about 1 μB per supercells) are independent of the doping site, whereas (ii) the electronic spectra of these systems differ drastically: La2O3:N with six-fold coordinated nitrogen behaves as a narrow-band-gap magnetic semiconductor, whereas with four-fold coordinated nitrogen is predicted to be a magnetic half-metal. This effect is explained taking into account the differences in N-2pz versus N-2px,y orbital splitting for various doping sites. Thus, the type of the doping site is one of the essential factors for designing of new d0-magnetic materials with promising properties.

cond-mat.mtrl-sci↗