Charge ordering in Ir dimers in the ground state of Ba5AlIr2O11

Vamshi Mohan Katukuri, Xingye Lu, Thorsten Schmitt, Vladimir N. Strocov, Oleg Yazyev
AMER PHYSICAL SOC, 2022
Journal paper

Abstract

It has been well established experimentally that the interplay of electronic correlations and spin-orbit interactions in Ir4+ and Ir5+ oxides results in insulating J(eff) = 1/2 and J(eff) = 0 ground states, respectively. However, in compounds where the structural dimerization of iridium ions is favorable, the direct Ir d-d hybridization can be significant and takes a key role. Here, we investigate the effects of direct Ir d-d hybridization in comparison with electronic correlations and spin-orbit coupling in Ba5AlIr2O11, a compound with Ir dimers. Using a combination of ab initio many-body wave-function quantum chemistry calculations and resonant inelastic x-ray scattering experiments, we elucidate the electronic structure of Ba5AlIr2O11. We find excellent agreement between the calculated and the measured spin-orbit excitations. Contrary to expectations, the analysis of the many-body wave function shows that the two Ir (Ir4+ and Ir5+) ions in the Ir2O9 dimer unit in this compound preserve their local J(eff) character close to 1/2 and 0, respectively. The local point group symmetry at each of the Ir ions plays an important role, significantly limiting the direct d-d hybridization. Our results emphasize that minute details in the local crystal field environment can lead to dramatic differences in the electronic states in iridates and 5d oxides in general.

Official source

https://infoscience.epfl.ch/record/293051?ln=en

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related concepts

Related publications

Investigations of the non-adiabatic photophysics of Cu(I)-phenanthroline complexes

Gloria Capano

Cu(I)-phenanthrolines are an important class of metal-organic molecules that exhibits much promise for solar energy harvesting and solar-driven catalysis applications. Although many experimental studies have been performed calling for high-level simulations to elucidate their photophysics, a complete picture is still missing. This is the goal of the present thesis. On the ultrafast (femtosecond) timescale we studied the non-adiabatic relaxation of a prototypical Cu(I)-phenanthroline, [Cu(dmp)2]+, by performing excited state simulations using two approaches: quantum dynamics and trajectory surface hopping. These simulations help to identify several mechanisms, internal conversion, pseudo Jahn-Teller distortion, intersystem crossing, occurring in the subpicosecond time scale. Surprisingly, we have found that intersystem crossing does not take place between the lowest singlet and triplet excited states, as previously proposed, but between the lowest singlet and higher triplet states. Moreover, we observed the initial stages (< 100 fs) of the solvent reorganization due to the electronic density changes in the excited state. This leads to an energy stabilization of the excited states that is associated with an increase of the non-radiative decay rate. The quantum dynamics simulations allowed us to provide indications for performing additional spectroscopy measurements by using the recently developed X-ray Free Electron Lasers (X-FELs). This technology can monitor both electronic and structural changes with an unprecedented time resolution of tens of femtoseconds and, therefore, is capable of revealing the aforementioned processes. In addition, we questioned the feasibility of such experiments and calculated the signal strengths for XAS and XES transient spectra. Finally, we analyzed the luminescence quenching, which has been observed for all Cu(I)-phenanthroline complexes when they are dissolved in strongly donating solvents. By performing Molecular Dynamics calculations we showed that, in contrast with the previously accepted model based on the formation of an exciplex (a species formed by two molecules, one in the excited state and one in the ground state), no stable exciplex is formed and that quenching is due to electrostatic solute-solvent interactions. In addition, we investigated how the geometry configuration can affect the luminescence lifetime in these molecules. We found a correlation between rigidity of the copper complex - inhibition of the pseudo Jahn-Teller distortion - and lifetime of the emission. The more the metal complex retains the ground state structure (large substituents), the longer its lifetime. This effect is attributed to a higher energy gap (excited state minus ground state energy) due to the reduction of relaxation. Our research reveals important insights into the relaxation mechanism and the complex interplay between geometry and electronic structure in Cu(I)-phenanthroline. These results can be exploited for guiding the synthesis of complexes with the desired physical properties.

EPFL2016

, , , , ,

We performed a combined theoretical and experimental investigation of the orbital magnetism and magnetocrystalline anisotropy of isolated Co and Fe adatoms on Pd(111) and Rh(111). Theoretical calculations of the spin and orbital moments are based on ab initio spin-polarized density-functional theory (DFT) including a self-consistent treatment of spin-orbit coupling. The calculations use a slab model to represent the adsorbate/substrate complex and allow for a complete structural relaxation leading to a strong inward displacement of the adatom and modest vertical and lateral relaxations in the substrate atoms. Compared to an idealized geometry where the atoms are kept on bulk lattice positions up to the surface, relaxation leads to a much stronger adatom/ligand hybridization. This is also reflected in the results for orbital moments and magnetocrystalline anisotropy energy (MAE). The enhanced hybridization leads to strong quenching of the adatom orbital moments but also to the formation of large induced spin and orbital moments in the substrate. As a consequence, we find that the substrate contribution to the MAE is much more important than estimated before on the basis of studies using an idealized geometry. We also find the surprising result that the MAE strongly depends on the adsorption site. The magnitude and even the sign of the MAE change for adatoms on face-centered cubic with respect to the ones on hexagonal close-packed hollow sites on the (111) surface. The dependence of the MAE on the combination of adatom and substrate has been analyzed in terms of the electronic structure, leading to a sound physical picture of the origin of the MAE. A fundamental problem, however, is the correct prediction of the size of the orbital moments of the adatoms. We suggest that this problem can be solved only via post-DFT corrections introducing an orbital dependence of the exchange potential. The theoretical results are compared to site-averaged, element-specific x-ray magnetic circular dichroism (XMCD) measurements. Low-temperature XMCD spectra and magnetization curves reveal weak out-of-plane anisotropy for Fe adatoms on both substrates. Interestingly, Co adatoms on Rh(111) present in-plane anisotropy with MAE of about -0.6 meV, contrary to the known out-of-plane anisotropy of Co on Pd(111) and Pt(111). The orbital to spin magnetic-moment ratio measured by XMCD shows that the Co adatoms present much stronger orbital magnetization components compared to Fe. The connection between orbital moments and MAE is discussed at the theoretical level including the contribution of the induced substrate magnetization.

2010

Superconductivity in F-doped LaFeAsO, Tc= 26 K was first reported by Kamihara et al in 2008. Following that, more iron-based superconductors, e.g., (Ba,K)Fe2As2, LiFeAs, and Fe1+yTe1-xSex were discovered. The new class of high Tc superconductors have attracted a tremendous interest. Iron-chacogenides do not involve arsenic but share several common features with the iron-pnictides. They are characterized by FeCh layers which are isostructural to the FeAs or FeP layers in the iron-pnictides. The electronic structure near the Fermi energy derives from the Fe 3d orbitals. Both families exhibit a spin density wave (SDW) ground state. Se substation for Te in FeTe suppresses the SDW and leads to superconductivity. From a more practical point of view, the iron-chacogenides have a rather simple structure, and they are less toxic and easier to obtain in large single crystals than the arsenide counterparts. For all these properties, the iron-chalcogenides are ideal compounds for angle-resolved photoemission (ARPES) studies. In this thesis, I have investigated by ARPES the normal state electronic structure of Fe1+yTe1-xSex superconductors with various doping level. I have studied the multi-orbital Fermi surface of Fe1+yTe1-xSex, mainly by means of polarized photons from synchrotron radiation sources. Individual bands of different orbital characters could then be distinguished by exploiting ARPES selection rules. I have also investigated the 3D electronic structure of these materials by performing normal emission measurements as a function of the incident photon energy. Namely, by using photon energies as large as 150 eV, I have performed an unusually broad ARPES survey of momentum space. The data reveal two inequivalent Fermi contours at nominally equivalent Gamma points in different Brillouin zones. The observed periodicity corresponds to a unit cell containing only one Fe atom, rather than the standard tetragonal unit cell containing two Fe atoms. I also observe a strong and selective suppression of spectral weight around perpendicular lines at the corner of the Brillouin zone.