Electron-like Sheets Research Articles

AbstAb-initio insights into the elastic, bonding, phonon, optoelectronic and thermophysical properties of SnTaS2

SnTaS2 is a layered topological semimetal exhibiting type-II low transition temperature superconductivity. Except some charge transport, electronic and superconductivity related properties, a number of the physical properties including elastic, mechanical, bonding, phonon dispersion, acoustic, thermal, and optical properties of SnTaS2 have not been explored comprehensively till now. In this work we have investigated all these physical properties of SnTaS2 employing the density functional theory (DFT) based first-principles methodology. It has been found that SnTaS2 is a mechanically stable, elastically anisotropic compound exhibiting strongly layered features. The bond hardness and Vickers hardness have been calculated. The material under study is ductile, soft and highly machinable. The chemical bonding has mixed character with significant contribution coming from the ionic channel. Phonon dispersion curves testify dynamical stability. Electronic band structure calculations show simple metallic character in agreement with previous results. The Fermi surface consists of both electron-like and hole-like sheets with varying degrees of energy dispersion. The low energy (encompassing the visible part of the optical spectrum) refractive index of SnTaS2 is high. The reflectivity is fairly nonselective over a wide range of photon energy and the absorption coefficient is large in the mid ultraviolet region. The Debye temperature and thermal conductivity of SnTaS2 are found to be low. The electron-phonon coupling constant has been calculated. SnTaS2 possesses optical anisotropy with respect to the polarization direction of the incident electric field.

Elastic, Electronic, Optical, Thermodynamic, and Superconducting Properties of CaMSi3 (M = Ir, Pt) and LaMSi3 (M = Ir, Rh) Superconductors: Insights from DFT-Based Computer Simulation

The structural, elastic, electronic, vibrational, optical, thermodynamic, and superconducting properties of potentially technologically important superconductors CaIrSi3, CaPtSi3, LaIrSi3, and LaRhSi3 have calculated by using density functional theory (DFT) with CASTEP code. The investigated results are compared with available experimental and theoretical values. All the calculated values are well agreed with the experimental and theoretical values. The single elastic moduli for all the compounds show mechanical stabilities under the Born stability conditions. The ductility nature appears from the value of Pugh ratio. The band structure shows that the material behaves metallic nature. The overall superior discussion of charge density and charge density difference map reveals the ionic, covalent, and metallic nature of noncentrosymmetric superconductors. The Fermi surface shows the hole and electron-like sheets. Various optical parameters are also investigated. The different optical and thermodynamic properties have also been observed in the present study. The reflectance spectrum reveals that these compounds have the influence to be used as a proficient solar reflector. The analyzed minimum thermal conductivity denotes the low thermal conductivity at ambient conditions. The Debye temperature has also been evaluated by using present single elastic constants data. The detailed study of the superconducting parameter indicates the phonon-mediated medium coupled BCS superconductors. The acquired knowledge in the present inquiry could provide a prominent encouragement for future theoretical studies.

Magnetic states and electronic properties of Sr4V2O6Fe2As2 studied by DFT calculations

In this work, we examine the magnetic stability of two incommensurate antiferromagnetic configurations and electronic band structures properties of Sr4V2O6Fe2As2 using first-principle density-functional-theory method. We show that the lowest total energy takes place in an incommensurate antiferromagnetic phase with the ordering wave vector q = (0.125, 0.125, 0) and ordered magnetic moment of 1.25 μB/V. Based on the total as well as partial density of states (DOS) data, it concludes that both Fe-3d and V-3d orbitals give a rise to DOS around Fermi level and lead to the occurrence of Van Hove singularity associated with electronic instability. A strong inter-band scattering in the incommensurate anti-ferromagnetic phases is proposed, since this behaviour is followed by a larger number of electronic bands crossing Fermi level as compared to those in nonmagnetic one. Electronic bands and Fermi surface data affirm multi-band structure superconductivity, where electron-like sheets of carriers with low Fermi velocities occur at the corner of the Brillouin zone and hole-like cylinders of carriers with high Fermi velocities situate around the Γ – Z line. Most importantly, our calculations predict the presence of both vertical and horizontal nodal lines, which seem to be distinct from usual feature of Fe-based superconductors with sole horizontal nodal lines.

Structural, elastic, electronic, bonding, and optical properties of topological CaSn3 semimetal

In recent days, topological semimetals have become an active branch of materials research. The topological Weyl semimetal CaSn3, belonging to the AuCu3 type cubic structure, is an important electronic system to investigate both from the point of view of fundamental physics and prospective applications. In this work, we have studied the structural, elastic, mechanical, electronic, bonding, Fermi surface and optical properties of CaSn3 in detail via first-principles method using the density functional theory. A comprehensive study of elastic constants and moduli shows that CaSn3 possesses low level of elastic anisotropy, reasonably good machinability, mixed bonding characteristics with ionic and covalent contributions, brittle nature and relatively high Vickers hardness with a low Debye temperature. The mechanical stability conditions are fulfilled. Analysis of bond population supports the bonding nature as indicated by the elastic parameters. The bulk electronic band structure reveals clear semimetallic features with signature Dirac cone-like dispersions near the Fermi level. A pseudogap in the electronic energy density of states at the Fermi level separating the bonding and the antibonding peaks points towards significant electronic stability of cubic CaSn3. The Fermi surface mostly consists of electron-like sheets with very few small hole pockets. The band structure is fairly isotropic in the k-space. The optical constants show interesting characteristics. The reflectivity spectra show almost non-selective behavior over a wide range of photon energy encompassing infrared to mid-ultraviolet regions. High reflectivity over wide spectral range makes CaSn3 a suitable material for reflecting coating. CaSn3 is an efficient absorber of ultraviolet radiation. The refractive index is very high in the infrared to visible range. All the energy dependent optical parameters exhibit clear metallic signatures and are in complete accord with the underlying bulk electronic density of states calculations.

Physical properties of niobium-based intermetallics (Nb3B; B = Os, Pt, Au): a DFT-based ab-initio study

Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic compounds Nb3B (B = Os, Pt, Au) have been revisited using first principles calculations based on the density functional theory (DFT). All these show excellent agreement with previous reports. More importantly, electronic bonding, charge density distribution and Fermi surface features have been studied in detail for the first time. Vickers hardness of these compounds is also calculated. The Fermi surfaces of Nb3B contain both hole- and electron-like sheets, the features of which change systematically as one move from Os to Au. The electronic charge density distribution implies that Nb3Os, Nb3Pt and Nb3Au have a mixture of ionic and covalent bondings with a substantial metallic contribution. The charge transfer between the atomic species in these compounds has been explained via the Mulliken bond population analysis and the Hirshfeld population analysis. The bonding properties show a good correspondence to the electronic band structure derived electronic density of states (DOS) near the Fermi level. Debye temperature of Nb3B (B = Os, Pt, Au) has been estimated from the elastic constants and shows a systematic behavior as a function of the B atomic species. A good correspondence among the elastic, electronic and charge density distribution properties are found. The superconducting transition temperature is found to be dominated by the electronic density of states at the Fermi level. We have discussed possible implications of the results obtained in this study in details in this paper.

CsFe4-δSe4: A Compound Closely Related to Alkali-Intercalated FeSe Superconductors.

We report the synthesis and characterizations of a new FeSe-based compound CsFe4-δSe4, which is closely related to alkali intercalated FeSe superconductors while exhibits distinct features. It does not undergo phase separation and antiferromagnetic transition. Powder neutron diffractions, electron microscopy and high-angle annular-dark-field images confirm that CsFe4-δSe4 possesses an ordered Cs arrangement as √2 × √2 superstructure, evidencing a B-centered orthorhombic lattice with a space group of Bmmm. The temperature-dependent powder neutron diffractions indicate no structural and magnetic transition from 320 to 5 K. In contrast to the symmetry-breaking in FeSe, this phase naturally possesses the orthorhombic symmetry even at room temperature. DFT calculations and transport measurements reveal a novel Fermi surface geometry with two electron-like sheets centered on Γ point and intermediate density of states at the Fermi level comparing with the value of FeSe and the superconducting A xFe2Se2.

First-principles study of electronic structure and Fermi surface in semimetallic YAs

In the course of searching for new systems, which exhibit nonsaturating and extremely large positive magnetoresistance, electronic structure, Fermi surface, and de Haas-van Alphen characteristics of the semimetallic YAs compound were studied using the all-electron full-potential linearized augmented-plane wave (FP–LAPW) approach in the framework of the generalized gradient approximation (GGA). In the scalar-relativistic calculation, the cubic symmetry splits fivefold degenerate Y-d orbital into low-energy threefold-degenerate t2g and twofold degenerate doublet e1g states at Γ point around the Fermi energy. One of them, together with the threefold degenerate t1u character of As-p orbital, render the YAs semimetal with a topologically trivial band order and fairly low density of states at the Fermi level. Including spin–orbit (SO) coupling into the calculation leads to pronounced splitting of the t1u state and shifting the bands in the energy scale. Consequently, the determined four different 3-dimensional Fermi surface sheets of YAs consists of three concentric hole-like bands at Γ and one ellipsoidal electron-like sheet centred at the X points. In full accordance with the previous first-principles calculations for isostructural YSb and YBi, the calculated Fermi surface of YAs originates from fairly compensated multi-band electronic structures.

Electronic structure and magnetism of RbGd2Fe4As4O2

Abstract The electronic structure, magnetism, and Fermi surface (FS) nesting of new superconductor RbGd2Fe4As4O2 (12442) were studied by the first-principes calculation. Its calculated ground state is the stripe antiferromagnetic state. The hole-like FSs will overlap with the electron-like FS sheets by the electron doping. Such significant FS nesting induces a peak of the bare susceptibility χ 0 ( q → ) at the X point, suggesting the parent compound RbGd2Fe4As4O2 is a self hole-doping induced superconductor.

Electronic Structure and Magnetism of the Multiband New Superconductor CaRbFe4As4

By first-principles calculations, we investigated the electronic structure, magnetism, and Fermi surface (FS) nesting of the newly discovered superconductor CaRbFe4As4. In the nonmagnetic (NM) state, there are ten bands crossing the Fermi level, which is more complicated than other FeAs-based superconductors, showing a multiband character. The FS consists of six holelike sheets around the Γ-point and four electronlike sheets near the Brillouin zone corner M-point. The holelike FSs will overlap with the electronlike FS sheets, if they are shifted by the vector \(\boldsymbol{{q}} = (\pi ,\pi ,0)\). Such FS nesting induces the bare susceptibility peak \(\chi _{0}(\boldsymbol{{q}})\) at the M-point. Fixed spin moment calculations indicate that CaRbFe4As4 has a strong tendency towards magnetism. Total energy calculations predicted that the ground state of CaRbFe4As4 is the stripe antiferromagnetic state. Therefore, CaRbFe4As4 is strongly similar to other FeAs-based superconductors, although it crystallized wit...

Self-hole-doping–induced superconductivity in KCa2Fe4As4F2

The electronic structure, magnetism, Fermi surface nesting, and bare susceptibility of the superconductor KCa2Fe4As4F2 are discussed in relation to the Fe-pnictide superconductors based on the first-principle calculations. There are ten bands crossing the Fermi level in the nonmagnetic (NM) states, resulting in six hole-like Fermi surface (FS) sheets along the line and four electron-like FS sheets along the line. It is more complicated than other FeAs-based superconductors, showing multi-bands character. Fixed spin moment calculations and the total energies of different magnetic phase indicate that KCa2Fe4As4F2 has a strong tendency towards magnetism, i.e., the stripe antiferromagnetic state. But the self-hole-doping suppressed the spin-density wave state, and then induced superconductivity in the parent compound. Such self-doping strategy may be used for future exploration of new superconductors.

The electronic structure of CeNiGe3 and YNiGe3 superconductors by ab initio calculations

Band structures of pressure-induced CeNiGe3 and exotic BCS-like YNiGe3 superconductors have been calculated employing the full-potential local-orbital code. Both the local density approximation (LDA) and LDA+U treatment of the exchange–correlation energy were used. The investigations were focused on differences between electronic properties of both compounds. Our results indicate that the Ce-based system exhibit a higher density of states at the Fermi level, dominated by the Ce 4f states, in contrast to its non-f-electron counterpart. The Fermi surface (FS) of each compound originates from three bands and consists of both holelike and electronlike sheets. The specific FS nesting properties of only CeNiGe3 enable an occurrence of spin fluctuations of a helicoidal antiferromagnetic character that may lead to unconventional pairing mechanism in this superconductor. In turn, the topology of the FS in YNiGe3 reveals a possibility of multi-band superconductivity, which can explain the observed anomalous jump at Tc in its specific heat.

Superconductivity and crystal structure of the palladium–iron–arsenides Ca10(Fe1− x Pd x As)10Pd3As8

The palladium–iron–arsenides Ca10(Fe1− x Pd x As)10(Pd3As8) were synthesized by solid-state methods and characterized by X-ray powder and single crystal diffraction. The triclinic crystal structure (space group P ) is isotypic to the homologue platinum 1038-type superconductors with alternating FeAs4/4- and Pd3As8-layers, each separated by layers of calcium atoms. Iron is tetrahedrally and palladium is planar coordinated by four arsenic atoms. As2-dimers (d As–As ≈ 250 pm) are present in the Pd3As8-layer. Even though each layer itself has a four-fold rotational symmetry, the shifted layer stacking causes the triclinic space group. Resistivity measurements of La-doped samples show the onset of superconductivity at 17 K and zero resistivity below 10 K. The magnetic shielding fraction is about 20 % at 3.5 K. 57Fe-Mössbauer spectra exhibit one absorption line and show no hint to magnetic ordering. The electronic structure is very similar to the known iron–arsenides with cylinder-like Fermi surfaces and partial nesting between hole- and electron-like sheets. Our results show that superconductivity in the palladium–iron-compounds is present but complicated by too high substitution of iron by palladium in the active FeAs-layers. Since the electronic preconditions are satisfied, we expect higher critical temperatures in Pd1038-compounds with lower or even without Pd-doping in the FeAs-layer.

Electronic structure of the heavy-fermion superconductor Ce2Ni3Ge5 and its reference Ce2Ni3Si5 compound by ab initio calculations

Band structures of the pressure-induced, heavy-fermion superconductor Ce2Ni3Ge5 and its non-superconducting, mixed-valence isostructural (Ibam) counterpart Ce2Ni3Si5 have been calculated employing the full-potential local-orbital code. Both the local density approximation (LDA) and LDA+U approaches were applied. These investigations were focused particularly on the topology of the Fermi surfaces (FSs) of the compounds. The results show that the FSs are quite similar in these systems and exist in four bands, containing three-dimensional holelike and electronlike sheets. However, the specific FS nesting properties has been revealed only in Ce2Ni3Ge5. They support a previously postulated presence of antiferromagnetic spin fluctuations (SF) in the heavy-fermion superconducting state of this germanide under pressure. Such SF can be responsible for the pressure-induced unconventional superconductivity in this system.

Weak-coupling superconductivity in electron-doped NaFe0.95Co0.05As revealed by ARPES

We report a systematic study on the electronic structure and superconducting (SC) gaps in electron-doped NaFe${}_{0.95}$Co${}_{0.05}$As superconductor using angle-resolved photoemission spectroscopy. Holelike Fermi sheets are at the zone center and electronlike Fermi sheets are at the zone corner, and are mainly contributed by $xz$ and $yz$ orbital characters. Our results reveal a $\frac{\ensuremath{\Delta}}{{K}_{B}{T}_{c}}$ in the range of 1.8--2.1, suggesting a weak-coupling superconductivity in these compounds. Gap closing above the transition temperature (${T}_{c}$) shows the absence of pseudogaps. Gap evolution with temperature follows the BCS gap equation near the $\ensuremath{\Gamma}$, $Z$, and $M$ high symmetry points. Furthermore, an almost isotropic superconductivity along the ${k}_{z}$ direction in the momentum space is observed by varying the excitation energies.

Electronic structure of the 344-type superconductors La3(Ni;Pd)4(Si;Ge)4 by ab initio calculations

Electronic structures of superconducting ternaries: La3Ni4Si4, La3Ni4Ge4, La3Pd4Si4, La3Pd4Ge4, and their non-superconducting counterpart, La3Rh4Ge4, have been calculated employing the full-potential local-orbital method within the density functional theory. Our investigations were focused particularly on densities of states (DOSs) at the Fermi level with respect to previous experimental heat capacity data, and Fermi surfaces (FSs) being very similar for all considered here compounds. In each of these systems, the FS originating from several bands contains both holelike and electronlike sheets possessing different dimensionality, in particular quasi-two-dimensional cylinders with nesting properties. A comparative analysis of the DOSs and FSs in these 344-type systems as well as in nickel (oxy)pnictide and borocarbide superconductors indicates rather similar phonon mechanism of their superconductivity.

Electronic structure and Fermi surface of iron-based superconductors R2Fe3Si5 (R = Lu;Y;Sc) from first principles

Electronic structures of three superconducting rare-earth iron silicides (Lu;Y;Sc)2Fe3Si5 and non-superconducting Lu2Ru3Si5, adopting a tetragonal crystal structure (P4/mnc), have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused particularly on the band structures and Fermi surfaces, existing in four bands and containing rather three-dimensional electronlike and holelike sheets. They support an idea of unconventional multi-band superconductivity in these ternaries, proposed earlier by other authors for Lu2Fe3Si5, based on heat-capacity, resistivity, electromagnetic and muon spin rotation measurements. Finally, a discussion on differences in the electronic structures between the investigated here and other common families of iron-based superconductors is carried out.

Electronic structure of superconducting Lu 2Ni 3Si 5 and its reference compound Y 2Ni 3Si 5 by ab initio calculations

Electronic structures of orthorhombic ternary nickel silicides: superconducting Lu 2Ni 3Si 5 and its non-superconducting counterpart, Y 2Ni 3Si 5, have been calculated employing the fully relativistic and full-potential local-orbital method within the density functional theory. Our investigations were focused particularly on the band structures and Fermi surfaces (FSs), being very similar for both ternaries. It appears that their FSs exist in four bands and contain electronlike and holelike three-dimensional sheets and small pockets, which suggests a presence of two- or even multi-band superconductivity (SC) in Lu 2Ni 3Si 5. The main difference between both systems is that only in Lu 2Ni 3Si 5 small electron FS pockets occur around the Γ point. It allows for arising BCS-like SC in this compound, as was deduced from previous heat-capacity measurements, while no sign of SC has been detected (at least down to 2 K) in Y 2Ni 3Si 5. In the latter system, a possible formation of a ferromagnetic ground state, which usually tends to destroy SC, has been excluded by our calculations.

Quantum oscillation studies of the Fermi surface of LaFePO

We review recent experimental measurements of the Fermi surface of the iron–pnictide superconductor LaFePO using quantum oscillation techniques. These studies show that the Fermi surface topology is close to that predicted by first principles density functional theory calculations, consisting of quasi-two-dimensional electron-like and hole-like sheets. The total volume of the two hole sheets is almost equal to that of the two electron sheets, and the hole and electron Fermi surface sheets are close to a nesting condition. No evidence for the predicted three-dimensional pocket arising from the Fe d z 2 band is found. Measurements of the effective mass suggest a renormalisation of around two, close to the value for the overall band renormalisation found in recent angle resolved photoemission measurements.

Sheet Dependence on Superconducting Gap in Oxygen-Deficient Iron-Based Oxypnictide Superconductors NdFeAsO0.85

Photoemission spectroscopy with low-energy tunable photons on oxygen-deficient iron-based oxypnictide superconductors NdFeAsO 0.85 ( T c =52 K) reveals a distinct photon-energy dependence of the electronic structure near the Fermi level ( E F ). A clear shift of the leading-edge can be observed in the superconducting states with 9.5 eV photons, while a clear Fermi cutoff with little leading-edge shift can be observed with 6.0 eV photons. The results are indicative of the superconducting gap opening not on the hole-like ones around Γ(0,0) point but on the electron-like sheets around M(π,π) point.

Multiple gaps and superfluid density from interband pairing in a four-band model of the iron oxypnictides

We study a four-band model for the iron oxypnictides, in which the superconducting properties are assumed to be determined by the interband coupling between holelike and electronlike Fermi sheets. We show that reasonable parameters can account for the angle-resolved photoemission spectra, showing multiple gaps in ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$, and for the temperature dependence of the superfluid density. At the same time, the zero-temperature value of the superfluid density shows a conventional scaling with the number of carriers.