arXiv subjects

D. A. Kukusta

Publications and source records attributed to D. A. Kukusta.

11 recordsLinked to original sources

arXiv2026

Resonant inelastic x-ray scattering in layered trimer iridate Ba4NbIr3O12: the density functional approach

We have investigated the electronic structure of Ba4NbIr3O12 within the density-functional theory (DFT) using the generalized gradient approximation while considering strong Coulomb correlations (GGA+U) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. Ba4NbIr3O12 has a quasi-2D structure composed of corner-connected Ba3NbIr3O12 rimers containing three distorted face-sharing IrO6 octahedra. The Ir atoms are distributed over two symmetrically inequivalent sites: the center of the trimer (Ir1) and its two tips (Ir2). The Ir1- Ir2 distance within the trimer is quite small and equals to 2.547 A, at low temperature. As a result, there is clear formation of bonding and antibonding states. The large bonding-antibonding splitting stabilizes the dzz-orbital-dominant antibonding state of 5d holes and produces a wide energy gap at the Fermi level. The ground state of Ba4NbIr3O12 is a nonmagnetic singlet with relatively moderate spin-orbit coupling (SOC). We have theoretically calculated the x-ray absorption spectroscopy (XAS) spectra at the Ir L2, and Nb L3 edges as well as the photoemission spectrum of Ba4NbIr3O12. We have also presented a comprehensive investigation of the resonant inelastic x-ray scattering (RIXS) spectra at the Ir L3$ O K, Nb K, L3, M3, M5, and N3 edges. The RIXS spectrum of Ba4NbIr3O12 at the Ir L3 edge possesses several sharp features below 2 eV corresponding to transitions within the Ir t2g levels. The peak located at 3.2 eV is found to be due to t2g to eg transitions. The high energy fine structure above 5.3 eV is mostly determined by 5dO to tg and O2p to eg transitions. The spectral features between 8 and 12 eV are due to 5dO to eg transitions.

cond-mat.str-el↗

arXiv2026

Resonant inelastic x-ray scattering in layered trimer iridate Ba4Ir3 O10 : the density functional approach

We have investigated the electronic structure of Ba4Ir3O10 within the density-functional theory (DFT) using the generalized gradient approximation while considering strong Coulomb correlations (GGA+U) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. Ba4Ir3O10 has a quasi-2D structure composed of buckled sheets, which constitute corner-connected Ir3O12 trimers containing three distorted face-sharing IrO6 octahedra. The Ir atoms are distributed over two symmetrically inequivalent sites: the center of the trimer (Ir1) and its two tips (Ir2). The Ir1 - Ir2 distance within the trimer is quite small and equals to 2.58 A at low temperature. As a result, the clear formation of bonding and antibonding states at the Ir1 site occurs. The large bonding-antibonding splitting stabilizes the dyz-orbital-dominant antibonding state of t2g holes and produces a wide energy gap at the Fermi level. However, the energy gap opens up only with taking into account strong Coulomb correlations at the Ir2 site. Therefore, we have quite a unique situation when the insulating state is driven by both the dimerization at the Ir1 site and Mott insulating behavior at the Ir2 one. We have investigated resonant inelastic x-ray scattering (RIXS) spectra at the Ir L3 edge. The calculated results are in good agreement with experimental data. The RIXS spectrum possesses several sharp features below 2.1 eV corresponding to transitions within the Ir t2g levels. The excitation located from 2.1 to 4.6 eV is due to t2g to eg and O2p to t2g transitions. The wide structure situated at 6.2-12 eV appears due to charge transfer and O2p to eg transitions. We have also presented comprehensive theoretical calculations of the RIXS spectrum at the oxygen K edge.

cond-mat.str-el↗

arXiv2025

Ab initio modeling of resonant inelastic x-ray scattering from Ca2RuO4

The single-layered perovskite Ca$_2$RuO$_4$, characterized by a 4$d^4$ electron configuration, has been studied from first principles using density functional theory (DFT) using the generalized gradient approximation, with inclusion of strong on-site Coulomb interactions and spin-orbit coupling (GGA+SO+$U$), in the framework of the fully relativistic, spin-polarized Dirac linear muffin-tin orbital (LMTO) band-structure method. This approach enabled a comprehensive investigation of the electronic structure of Ca$_2$RuO$_4$ through the modeling of relevant spectra obtained from synchrotron-based techniques widely used to probe electronic properties, with a primary focus on resonant inelastic X-ray scattering (RIXS) at the Ru $L_3$ and O $K$ edges. The calculated spectra were thoroughly analyzed with available experimental data reported in the literature. The good agreement between our results and experimental observations for Ca$_2$RuO$_4$ enables a conclusive interpretation of key features in the spectra obtained from the aforementioned techniques. Consequently, this enables us to describe its electronic properties and to establish a solid theoretical approach suitable for routine modeling of spectra, particularly from RIXS, aimed at characterizing the electronic structure and properties of similar or more complex strongly correlated, technologically relevant materials.

cond-mat.str-el↗

arXiv2025

Density functional theory of resonant inelastic x-ray scattering in the quasi-one-dimensional dimer iridate Ba$_5$AlIr$_2$O$_{11}$

We have investigated the electronic structure of Ba$_5$AlIr$_2$O$_{11}$ within the density functional theory using the generalized gradient approximation while considering strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We have investigated the x-ray absorption spectra, x-ray magnetic circular dichroism, and resonant inelastic x-ray scattering spectra (RIXS) at the Ir $K$, $L_3$ , $M_3$, $M_5$ and O K edges. The calculated results are in good agreement with experimental data. The RIXS spectrum of Ba$_5$AlIr$_2$O$_{11}$ at the Ir $L_3$ edge possesses sharp twelve features below 1.5 eV corresponding to transitions within the Ir t2g levels. The excitations located from 2 to 4 eV are due to $t_{2g} \to e_g$ and $O_{2p} \to t_{2g}$ transitions. The high energy peaks situated at 5-11 eV appear due to charge transfer transitions. The theory reproduces well the shape and polarization dependence of the oxygen O K RIXS spectrum. We have found that the dependence of the RIXS spectrum at the oxygen K edge on the incident photon energy and the momentum transfer vector Q is much stronger than the corresponding dependence at the Ir $L_3$ edge

cond-mat.str-el↗

arXiv2025

Density functional theory of resonant inelastic x-ray scattering in the quasi-one-dimensional dimer iridate Ba3InIr2O9

We have investigated the electronic structure of Ba3InIr2O9 within the density-functional theory (DFT) using the generalized gradient approximation while considering strong Coulomb correlations (GGA+$U$) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We have investigated resonant inelastic x-ray scattering (RIXS) spectra at the Ir L3 K edge. The calculated results are in good agreement with experimental data. The RIXS spectrum of Ba3InIr2O9 at the Ir L3 edge possesses several sharp features below 2 eV corresponding to transitions within the Ir tg levels. The excitation located from 2 to 5 eV is due to tg -> eg transitions. The third wide structure situated at 5-12 eV appears due to charge transfer transitions. We have also presented comprehensive theoretical calculations of the RIXS spectrum at the oxygen K edge.

cond-mat.str-el↗

arXiv2024

Electronic structure and resonant inelastic x-ray scattering in Ta2NiSe5

We study the electronic structure of Ta2NiSe5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ta L3 edge. We also investigate the electronic properties of Ta2NiSe5 within the density-functional theory using the generalized gradient approximation in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. While ARPES, dc transport, and optical measurements indicate that Ta2NiSe5 is a small band-gap semiconductor, DFT gives a metallic nonmagnetic solution in Ta2NiSe5 . To obtain the semiconducting ground state in Ta2 NiSe5 we use a self-interaction correction (SIC) procedure by introducing an orbital-dependent potential Vl into the Hamiltonian. We investigate theoretically the x-ray absorption spectroscopy (XAS) and RIXS spectra at the Ni and Ta L3 edges and analyze the spectra in terms of interband transitions. We investigate the RIXS spectra as a function of momentum transfer vector Q and incident photon energy. Because Ta2 NiSe5 possesses only fully occupied (Ni 3d and Se 4p) and completely empty (Ta 5d) shells with the formal valencies Ta5+ (5d0), Ni0 (3d10 ), and Se2- (4p6 ), both the Ni and Ta L3 RIXS spectra belong to a charge transfer type with ligand-to-metal excitations.

cond-mat.str-el↗

arXiv2024

Electronic structure and resonant inelastic x-ray scattering in Ca3Ru2O7

We have investigated the electronic structure of the transition metal oxide Ca3Ru2O7 within density functional theory using the generalized gradient approximation while considering strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. Ca3Ru2O7 can be classified as a Mott insulator since it was expected to be metallic from band structure calculations. We have investigated the resonant inelastic x-ray scattering spectra at the Ru and Ca K, L3, and M3 edges as well as at the O K edge. The experimentally measured resonance inelastic x-ray spectrum of Ca3Ru2O7 at the Ru L3 edge possesses a sharp feature below 2 electron-volts corresponding to transitions within the Ru t_2g levels. The excitation located from 2 to 4 electron-volts is due to t2g -> e_g transitions. The third wide structure situated at 4.5-11 electron-volts appears due to transitions between the Ru 4dO states derived from the tails of oxygen 2p states and t_2g and e_g states. The measured resonance inelastic x-ray spectra at the Ru L3 and M3 edges are very similar. However, the corresponding measured resonance inelastic x-ray spectra at the Ca site quite differ from each other due to the significant difference in the widths of core-levels.

cond-mat.str-el↗

arXiv2023

Resonant inelastic x-ray scattering of the Jeff = 1/2 Mott insulator Sr2IrO4 from the density-functional theory

We have investigated the electronic structure of Sr2IrO4 within the density-functional theory using the generalized gradient approximation while taking into account strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear MT orbital band structure method. We have investigated the x-ray absorption spectra, x-ray magnetic circular dichroism, and resonant inelastic x-ray scattering spectra at the Ir L3 and O K edges. The calculated results are in good agreement with the experimental data. The RIXS spectrum of Sr2IrO4 at the Ir L3 edge in addition to the elastic scattering peak at 0 eV possesses a sharp feature below 1.5 eV corresponding to transitions within the Ir t2g levels. The excitation located from 2 eV to 5 eV is due to t2g-eg transitions. The third wide structure situated at 5-12 eV appears due to transitions between the Ir 5d_O states derived from the tails of oxygen 2p states and eg and t2g states. The RIXS spectrum of Sr2IrO4 at the O K edge consists of three major inelastic excitations at 0.7 eV, 3.5 eV, and around 6.2 eV. We have found that the first low energy feature is due to interband transitions between occupied and empty O t2g transitions, which appear due to the strong hybridization between oxygen 2p and Ir t2g states in the close vicinity of the Fermi level. The next two peaks at around 3.5 and 6.2 eV reflect the interband transitions from the occupied O 2p states and the empty oxygen states which arise from the hybridization with Ir t2g and eg states, respectively. We have found that the theory reproduces well the shape and energy position of the low energy feature, but the second and the third peaks are shifted towards smaller energy in comparison with the experimental measurements.

cond-mat.str-el↗

arXiv2021

Resonant inelastic x-ray scattering spectra in the hyperhoneycomb iridate $β$-Li$_2$IrO$_3$: First principles calculations

We studied the electronic structure of $β$-Li$_2$IrO$_3$ insulator within the density-functional theory using the generalized gradient approximation with taking into account strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The $β$-Li$_2$IrO$_3$ undergoes a pressure-induced structural and magnetic phase transitions at $P_c$ $\sim$4 GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by the formation of Ir$_2$ dimers on the zigzag chains, with an Ir-Ir distance of $\sim$2.66~Å, even shorter than that of metallic Ir. The strong dimerization stabilizes the bonding molecular-orbital state, leads to the collapse of the magnetism and opens the energy gap with a concomitant electronic phase transition from a Mott insulator to band insulator. The resonant inelastic x-ray scattering spectra (RIXS) at the Ir $L_3$ edge were investigated theoretically from first principles. The calculated results are in good agreement with the experimental data. We show that the the drastic reconstruction of the RIXS spectral peak at 0.7 eV associated with the structural $Fddd \rightarrow C2/c$ phase transition at $P_c$ can be related to disappearing of the Coulomb correlations in the high-pressure $C2/c$ phase

cond-mat.str-el↗

arXiv2018

Origin of magnetic anisotropy in doped Ce$_2$Co$_{17}$ alloys

Magnetocrystalline anisotropy (MCA) in doped Ce$_{2}$Co$_{17}$ and other competing structures was investigated using density functional theory. We confirmed that the MCA contribution from dumbbell Co sites is very negative. Replacing Co dumbbell atoms with a pair of Fe or Mn atoms greatly enhance the uniaxial anisotropy, which agrees quantitatively with experiment, and this enhancement arises from electronic-structure features near the Fermi level, mostly associated with dumbbell sites. With Co dumbbell atoms replaced by other elements, the variation of anisotropy is generally a collective effect and contributions from other sublattices may change significantly. Moreover, we found that Zr doping promotes the formation of 1-5 structure that exhibits a large uniaxial anisotropy, such that Zr is the most effective element to enhance MCA in this system.

cond-mat.mtrl-sci↗

arXiv2012

Unusual magnetism of layered chromium sulfides MCrS2 (M=Li, Na, K, Ag, and Au)

MCrS2 compounds (M=Li, Na, K, Cu, Ag, and Au) with triangular Cr layers show large variety of magnetic ground states ranging from 120-degree antiferromagnetic order of Cr spins in LiCrS2 to double stripes in AgCrS2, helimagnetic order in NaCrS2, and, finally, ferromagnetic Cr layers in KCrS2. On the base of ab-initio band structure calculations and an analysis of various contributions to exchange interactions between Cr spins we explain this tendency as originating from a competition between antiferromagnetic direct nearest-neighbor d-d exchange and ferromagnetic superexchange via S p states which leads to the change of the sign of the nearest neighbor interaction depending on the radius of a M ion. It is shown that other important interactions are the third-neighbor interaction in a layer and interlayer exchange. We suggest that strong magneto-elastic coupling is most probably responsible for multiferroic properties of at least one material of this family, namely, AgCrS2.

cond-mat.mtrl-sci↗