Based on First-principles calculation, we have investigated electronic structure of a ZrCuSiAs structured superconductor LaNiPO. The density of states, band structures and Fermi surfaces have been given in detail. Our results indicate that the bonding of the La-O and Ni-P is strongly covalent whereas binding property between the LaO and NiP blocks is mostly ionic. It's also found that four bands are across the Fermi level and the corresponding Fermi surfaces all have a two-dimensional character. In addition, we also give the band decomposed charge density, which suggests that orbital components of Fermi surfaces are more complicated than cuprate superconductors.
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 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.
Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which has the highest TC (about 4.6 K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi2Bi2O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electro…
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 f…
We present an ab initio $GW$ self-energy calculation of the electronic structure of LaNiO$_2$. With respect to density-functional theory we find that in $GW$ the La 4$f$ states undergo an important $+$2 eV upward shift from the Fermi level, while the O 2$p$ states are pulled down by $-$1.5 eV, thus reinforcing the charge-transfer character of this material. However, $GW$ many-body effects leave the $d$-like bands at the Fermi level almost unaffected, so that the Fermi-surface topology is preserved, unlike in cuprates.
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.
Cooper's one pair problem is investigated for a 2D lattice in the background of both passive and active Fermi sea in a weakly correlated environment. Boson exchange mechanisms involving excitons as well as phonons are invoked for pairing in the s- wave channel. The important quantities calculated are pairing energy and coherence length as functions of bosonic energy, attracted coupling constant and band filling factor. Comparison of our theoretical results with those from experiments on overdoped cuprate superconductors and other type of theoretical calculations show electronic mechanism to be…
The ThCr2Si2-type arsenide-selenide phase KFe2AsSe is proposed as a parent system for a new "intermediate" group of Fe-based superconducting materials bridging the known families of Fe-pnictides (such as BaFe2As2) and Fe-chalcogenides (such as KxFe2-ySe2) superconductors. The characterization of the proposed charge-balanced phase by means of FLAPW-GGA approach covers the crystal structure, As/Se atomic ordering, stability, electronic bands, Fermi surface, and density of electronic states.
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 3…
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 sys…
We report full-potential density functional theory (DFT)-based {\it ab initio} band structure calculations to investigate electronic structure properties of the first pnictide superconductor with a honeycomb-lattice structure: SrPtAs. As a result, electronic bands, density of states, Fermi velocities and the topology of the Fermi surface for SrPtAs are obtained. These quantities are discussed in comparison to the first available experimental data. Predictions for future measurements are provided.
The detailed information of the electronic structure is the key for understanding the nature of charge density wave (CDW) order and its relationship with superconducting order in microscopic level. In this paper, we present high resolution laser-based angle-resolved photoemission spectroscopy (ARPES) study on the three-dimensional (3D) hole-like Fermi surface around the Brillouin zone center in a prototypical qusi-one-dimensional CDW and superconducting system ZrTe3. Double Fermi surface sheets are clearly resolved for the 3D hole-like Fermi surface around the zone center. The 3D Fermi surface…
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 r…
Cooper's formalism for fermionic pairing has been revisited considering upto 3rd neighbour hopping terms, firstly with a Fermi liquid like background on a square lattice keeping in mind the overdopped cuprates. Then the whole scheme is repeated with a Marginal Fermi liquid- like background, taking into account the self energy correction of the mobile electrons to include a more realitic density of states in the calculation. Detailed comparison of our theoretical results with those from experiments strongly supports the Marginal Fermi liquid- like character of the normal phase with exciton medi…
The particle-hole asymmetry electronic state of cuprate superconductors and the related doping and temperature dependence of the Fermi arc length are studied based on the kinetic energy driven superconducting mechanism. By taking into account the interplay between the SC gap and normal-state pseudogap, the essential feature of the evolution of the Fermi arc length with doping and temperature is qualitatively reproduced. It is shown that the particle-hole asymmetry electronic state is a natural consequence due to the presence the normal-state pseudogap in the particle-hole channel. The Fermi ar…
We report electronic structure calculations for BaTi$_2$Sb$_2$O and discuss the results in relation to the observed superconductivity of this material when hole doped with Na. The Fermi surface shows several sheets. These include a nested nearly 2D cylinder. There are also two sheets, which are three dimensional, in spite of the layered crystal structure. A magnetic instability associated with Fermi surface nesting is found. A sign-changing s-wave state, different from the one in the Fe-based superconductors, is predicted within a scenario of spin-fluctuation mediated superconductivity.
We suggest a model for electronic structure of cuprate superconductors that makes it possible to describe evolution of this structure with the doping and provides a new explanation for a number of typical features of cuprates, including the pseudogap and the Fermi arcs. According to this model, the unique electronic structure of cuprates is favorable for the formation of two-atomic negative-U centers (NUCs) and realization of a peculiar mechanism of the electron-electron interaction.
The electronic structures of BaAlGe and SrAlGe which are superconductors with hexagonal honeycomb layers have been studied by using a first principles method. Energy bands, Fermi surafces, and density of states are presented. The two materials have topologically different Fermi surfaces. BaAlGe has two Fermi surfaces: One has a three dimensional spinning-top-like shape and the other has a cylindrical shape with two dimensional character. SrAlGe has only one connected Fermi surface. Two gap superconductivity for BaAlGe is suggested from the inherently different character of the two Fermi surfac…
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 tem…
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 th…
We have studied the low-lying electronic structure of a new ThCr$_2$Si$_2$-type superconductor KNi$_2$Se$_2$ with angle-resolved photoemission spectroscopy. Three bands intersect the Fermi level, forming complicated Fermi surface topology, which is sharply different from its isostructural superconductor K$_x$Fe$_{2-y}$Se$_2$. The Fermi surface shows weak variation along the $k_z$ direction, indicating its quasi-two-dimensional nature. Further comparison with the density functional theory calculations demonstrates that there exist relatively weak correlations and substantial hybridization of th…
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 Lu2Fe…
The low temperature dependence of the spin and charge susceptibilities of an anisotropic electron system in two dimensions is analyzed. It is shown that the presence of inflection points at the Fermi surface leads, generically, to a $ T \log T $ dependence, and a more singular behavior, $χ\sim T ^{3/4} \log T$, is also possible. Applications to quasi two-dimensional materials are discussed.
The band structure of the new perovskite-like superconductor MgCNi$_{3}$ was studied by the self-consistent FP-LMTO method. The superconducting properties of MgCNi$_{3}$ are associated with an intensive peak in the density of Ni3d states near the Fermi level. The absence of superconductivity for nonstoichiometric compositions MgC$_{1-x}$Ni$_{3}$ is due to the transition of the system to the magnetic state. The possibility of superconductivity was discussed for intermetallics ScBNi$_{3}$, InBNi$_{3}$, MgCCo$_{3}$ and MgCCu$_{3}$ which are isostructural with MgCNi$_{3}$.
By using a relativistic linear augmented-plane-wave method, we clarify energy band structure and the Fermi surfaces of recently synthesized thorium compound ThRhIn$_5$. We find several cylindrical Fermi surface sheets, which are similar to those of CeTIn$_5$ (T=Ir and Co), PuTGa$_5$ (T=Co and Rh), and AmCoGa$_5$. We discuss such similarity among the compounds including rare-earth or actinide ions with different $f$ electron numbers.
We report an angular quantum oscillation study of Tl_2Ba_2CuO_{6+delta} for two different doping levels (Tc = 10K and 26 K) and determine the Fermi surface size and topology in considerable detail. Our results show that Fermi liquid behavior is not confined to the edge of the superconducting dome and is robust up to at least T_c^{max}/3.5. Superconductivity is found to survive up to a larger doping p_c = 0.31 than in La_{2-x}Sr_xCuO_4. Our data imply that electronic inhomogeneity does not play a significant role in the loss of superconductivity and superfluid density in overdoped cuprates, and…
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…
We studied the electronic structures of LaOFeP under applied pressure using first-principles calculations. The electronic density of states at the Fermi level decreases continuously with increasing pressure. The electron branches of Fermi surfaces are rather robust to pressure, while the hole branches change significantly. Two hole surfaces shrink into small ellipsoid-like surfaces and disappear finally, at which the applied pressure is ~ 74.7 GPa. The pressure response can be understood by the band structures around the Fermi level. Comparative studies reveal that the disappearance of hole su…
A theory of electronic Raman scattering in nearly antiferromagnetic Fermi liquids is constructed using the phenomenological electron-electron interaction introduced by Millis, Monien, and Pines. The role of "hot spots" and their resulting signatures in the channel dependent Raman spectra is highlighted, and different scaling regimes are addressed. The effects of self consistency and vertex corrections are compared to a perturbative treatment of the interaction. The theory is then compared to Raman spectra taken in the normal state of cuprate superconductors, and it is shown that many features …
We report electronic structure calculations for the layered centrosymmetric superconductor LaNiGa$_2$, which has been identified as having a possible triplet state based on evidence for time reversal symmetry breaking. The Fermi surface has several large sheets and is only moderately anisotropic, so that the material is best described as a three dimensional metal. These include sections that are open in the in-plane direction as well as a section that approaches the zone center. The density of states is high and primarily derived from Ga $p$ states, which hybridize with Ni $d$ states. Comparin…
We present LDA band structure of novel hole doped high temperature superconductors (Tc~30K) KxFe2Se2 and CsxFe2Se2 and compare it with previously studied electronic structure of isostructural FeAs superconductor BaFe2As2 (Ba122). We show that stoichiometric KFe2Se2 and CsFe2Se2 have rather different Fermi surfaces as compared with Ba122. However at about 60% of hole doping Fermi surfaces of novel materials closely resemble those of Ba122. In between these dopings we observe a number of topological Fermi surface transitions near the G point in the Brillouin zone. Superconducting transition temp…
The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the HfB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron-phonon spectral functions, electrical …
We construct minimal electronic models for a newly discovered superconductor LaO$_{1-x}$F$_x$BiS$_2$ ($T_c=$ 10.6K) possessing BiS$_2$ layers based on first principles band calculation. First, we obtain a model consisting of two Bi $6p$ and two S $3p$ orbitals, which give nearly electron-hole symmetric bands. Further focusing on the bands that intersect the Fermi level, we obtain a model with two $p$ orbitals. The two bands (per BiS$_2$ layer) have quasi-one-dimensional character with a double minimum dispersion, which gives good nesting of the Fermi surface. At around $x\sim 0.5$ the topology…
Obtaining the electronic structure of the newly discovered iron-based superconductors is the key to understanding the mechanism of their high-temperature superconductivity. We used angle-resolved photoemission spectroscopy (ARPES) to make direct measurements of the electronic structure and Fermi surface (FS) of the untwinned uniaxial state of CaFe2As2, the parent compound of iron-based superconductors. We observed unequal dispersions and FS geometries along the orthogonal Fe-Fe bond directions. More importantly, unidirectional straight and flat FS segments are observed near the zone center, wh…
The electronic structures of R2Fe3Si5 (where R = Lu, Tm, Er, Tb, Yb) intermetallics have been calculated from first principles in local-spin density (LSDA) and LSDA + U approaches. The majority of rare-earth iron silicides, except for the heavy-fermion Yb-based compound, exhibit almost equal values of density of states at the Fermi level (EF) as well as very similar Fermi surface topology. The electronic structure around EF in the 235-type Fe-based compounds is completely dominated by the Fe 3d states. Thus the different superconducting properties of some members of the R2Fe3Si5 family are rat…
The electronic structure of layered Sr$_{3}$Ru$_{2}$O$_{7}$ in its orthorhombic structure is investigated using density functional calculations. The band structure near the Fermi energy, consists of Ru $% t_{2g}$ states hybridized with O $p$ orbitals. The $yz$ and $xz$ bands, which are largely responsible for the nesting related antiferromagnetic spin fluctuations in Sr$_{2}$RuO$_{4}$ split pairwise into even and odd combinations due to the interlayer coupling reducing the strength of the nesting. The $xy$ bands show much less interplanar coupling as expected, and also less $c$-axis dispersion…
Using LDA+GTB (local density approximation+generalized tight-binding) hybrid scheme we investigate the band structure of the electron-doped high-$T_c$ material Sm$_{2-x}$Ce$_{x}$CuO$_4$. Parameters of the minimal tight-binding model for this system (the so-called 3-band Emery model) were obtained within the NMTO ($N$-th order Muffin-Tin orbital) method. Doping evolution of the dispersion and Fermi surface in the presence of electronic correlations was investigated in two regimes of magnetic order: short-range (spin-liquid) and long-range (antiferromagnetic metal). Each regime is characterized …
We introduce a simple model of the low energy electronic states in the vicinity of a vortex undergoing quantum zero-point motion in a d-wave superconductor. The vortex is treated as a point flux tube, carrying pi-flux of an auxiliary U(1) gauge field, which executes simple harmonic motion in a pinning potential. The nodal Bogoliubov quasiparticles are represented by Dirac fermions with unit U(1) gauge charge. The energy dependence of the local density of electronic states (LDOS) at the vortex center has no zero bias peak; instead, small satellite features appear, driven by transitions between …
The electronic structures of the ground state for several different superconducting materials, such as cuprates, conventional 3-dimensional superconductors, doped semiconductors and low-dimensional systems, are quite different and sometimes in contrast to what is supposed to make a superconductor. Properties like the Fermi-surface (FS) topology, density-of-states (DOS), stripes, electron-phonon coupling ($λ_{ep}$) and spin fluctuations ($λ_{sf}$) are analyzed in order to find clues to what might be important for the mechanism of superconductivity. A high DOS at $E_F$ is important for standard …
BaFe2S3 is a special iron superconductor with two-leg ladder structure which can help to unravel the role played by the electronic correlations in high-Tc superconductivity. At zero pressure it is insulating with stripe antiferromagnetic (AF) order and superconductivity emerges under pressure. We use a slave-spin technique to analyze the strength of the local correlations in BaFe2S3. We find that at the pressure at which the superconductivity appears the electronic correlations in BaFe2S3 are similar to the ones measured in other iron superconductors. However, at zero pressure the strength of …
The electronic structures of FeAs-compounds strongly depend on the Fe-As bonding, which can not be described successfully by the local density approximation (LDA). Treating the multi-orbital fluctuations from $ab$-$initio$ by LDA+Gutzwiller method, we are now able to predict the correct Fe-As bond-length, and find that Fe-As bonding-strength is 30% weaker, which will explain the observed "soft phonon". The bands are narrowed by a factor of 2, and the $d_{3z^2-r^2}$ orbital is pushed up to cross the Fermi level, forming 3-dimensional Fermi surfaces, which suppress the anisotropy and the ($π,π$)…
By paying special attention to the fact that the doped holes induce deformation of CuO6 octahedrons (or CuO5 pyramids) in cuprate superconductors, we develop a non-rigid band theory treating doping-induced alterations of energy-band structures in copper oxide superconductors. Thanks to this theory, we obtain a complete picture of the doping-induced alteration in the electronic structure of La2CuO4, from the spin-disordered insulating phase to the metallic phase. We conclude that the Fermi surface structure of this cuprate in the underdoped region consists of Fermi pockets in the antinodal regi…
In this paper we show that the optical conductivity can be calculated to agree with experiment if the details of the electronic states around the Fermi level are taken into account with some care. More precisely, we present a calculation of the optical conductivity in YBa2Cu3O7 on the basis of an exact (ab initio) three dimensional electronic band structure calculation from which we extract the information on the bands near the Fermi energy that can be associated to the CuO2 plane-carrier states. To simulate the superconducting state we superimpose a gap to these bands alone. On these basis, w…
We report a first study of low energy electronic structure and Fermi surface topology for the recently discovered iron-based superconductor Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase, with Tc = 8K), via angle-resolved photoemission spectroscopy (ARPES). Despite its triclinic crystal structure, ARPES results reveal a fourfold symmetric band structure with the absence of Dirac-cone-like Fermi dots (related to magnetism) found around the Brillouin zone corners in other iron-based superconductors. Considering that the triclinic lattice and structural supercell arising from the Pt3As8 intermediary lay…
We construct an effective Hamiltonian for the motion of T2g highly correlated states in NaxCoO2. We solve exactly a multiband model in a CoO6 cluster with electronic occupation corresponding to a nominal Co valence of either +3 or +4. Using the ensuing ground states, we calculate the effective O mediated hopping t=0.10 eV between many-body T2g states, and estimate the direct hopping t'~0.04 eV. The trigonal splitting 3D=0.315 eV is taken from recent quantum chemistry calculations. The resulting effective Hamiltonian is solved using a generalized slave-boson mean-field approximation. The result…
We investigate the electronic structure of a complex conventional superconductor, ZrB12 employing high resolution photoemission spectroscopy and ab initio band structure calculations. The experimental valence band spectra could be described reasonably well within the local density approximation. Energy bands close to the Fermi level possess t_(2g) symmetry and the Fermi level is found to be in the proximity of quantum fluctuation regime. The spectral lineshape in the high resolution spectra is complex exhibiting signature of a deviation from Fermi liquid behavior. A dip at the Fermi level emer…
A comprehensive first principles study on the electronic topological transition in a number of 122 family of Fe based superconductors is presented. Doping as well as temperature driven Lifshitz transitions are found from first principles simulations in a variety of Fe based superconductors that are consistent with experimental findings. In all the studied compounds the Lifshitz transitions are consistently found to occur at a doping concentration where superconductivity is highest and magnetism disappears. Systematically, the Lifshitz transition occurs in the electron Fermi surfaces for hole d…
We investigate the electronic structure of CaFe$_2$As$_2$ using high resolution photoemission spectroscopy. Experimental results exhibit three energy bands crossing the Fermi level making hole pockets around the $Γ$-point. Temperature variation reveal a gradual shift of an energy band away from the Fermi level with the decrease in temperature in addition to the spin density wave (SDW) transition induced Fermi surface reconstruction of the second energy band across SDW transition temperature. The hole pocket in the former case eventually disappears at lower temperatures while the hole Fermi sur…
The electronic structures of ThCr$_2$Si$_2$ structure BaCu$_2$As$_2$ and SrCu$_2$As$_2$ are investigated using density functional calculations. The Cu $d$ orbitals are located at 3 eV and higher binding energy, and are therefore chemically inert with little contribution near the Fermi energy. These materials are moderate density of states, sp-band metals with large Fermi surfaces and low anisotropy.
We present density functional theory (DFT) calculations and a full set of X-ray spectra (resonant inelastic X-ray scattering and X-ray photoelectron spectra) measurements of single crystal CaFe2As2. The experimental valence band spectra are consistent with our DFT calculations. Both theory and experiment show that the Fe 3d-states dominate the Fermi level and hybridize with Ca 3d-states. The simple shape of Xray photoelectron (XPS) Fe 2p-core level spectrum (without any satellite structure typical for correlated systems) suggests itinerant character of the Fe 3d-electrons. Based on the similar…
Band structure of metallic sodium cobaltate Na$_x$CoO$_2$ ($x$=0.33, 0.48, 0.61 0.72) has been investigated by local density approximation+Hubbard $U$ (LDA+$U$) method and within Gutzwiller approximation for the Co-$t_{2g}$ manifold. Correlation effects being taken into account results in suppression of the $e'_g$ hole pockets at the Fermi surface in agreement with recent angle-resolved photo-emission spectroscopy (ARPES) experiments. In the Gutzwiller approximation the bilayer splitting is significantly reduced due to the correlation effects. The formation of high spin (HS) state in Co $d$-sh…
This paper presents the comparative study of LDA calculated electronic structure of new isostructural to iron based systems superconductors (Sr,Ca)Pd2As2 with Tc about 1K and similar but structurally different system BaPd2As2. Despite chemical formula looks similar to iron superconductors and even main structural motif is the same - layers of Fe square lattices, electronic structure of (Sr,Ca)Pd2As2 and BaPd2As2 differs from Fe(As,Se)-HTSC completely. All these systems have essentially three dimensional Fermi surfaces in contrast to Fe(As,Se) materials. The Fermi level is crossed by low intens…
We have studied the nature of the three-dimensional multi-band electronic structure in the twodimensional triangular lattice Ir1-xPtxTe2 (x=0.05) superconductor using angle-resolved photoemission spectroscopy (ARPES), x-ray photoemission spectroscopy (XPS) and band structure calculation. ARPES results clearly show a cylindrical (almost two-dimensional) Fermi surface around the zone center. Near the zone boundary, the cylindrical Fermi surface is truncated into several pieces in a complicated manner with strong three-dimensionality. The XPS result and the band structure calculation indicate tha…
One challenge in contemporary condensed matter physics is to understand unconventional electronic physics beyond the paradigm of Landau Fermi-liquid theory. Here, we present a perspective that posits that most such examples of unconventional electronic physics stem from restrictions on the degrees of freedom of quantum electrons in Landau Fermi liquids. Since the degrees of freedom are deeply connected to the system's symmetries and topology, these restrictions can thus be realized by external constraints or by interaction-driven processes via the following mechanisms: (i) symmetry breaking, (…
Understanding electronic properties that violate the Landau Fermi liquid paradigm in cuprate superconductors remains a major challenge in condensed matter physics. The strange metal state in overdoped cuprates that exhibits linear-in-temperature scattering rate and dc resistivity is a particularly puzzling example. Here, we compute the electronic scattering rate in the two-dimensional Hubbard model using cluster generalization of dynamical mean-field theory. We present a global phase diagram documenting an apparent non-Fermi liquid phase, in between the pseudogap and Fermi liquid phase in the …
