Quasimolecular electronic structure of the trimer iridate Ba$_4$NbIr$_3$O$_{12}$
cond-mat.str-el
/ Authors
M. Magnaterra, A. Sandberg, H. Schilling, P. Warzanowski, L. Pätzold, E. Bergamasco, Ch. J. Sahle, B. Detlefs, K. Ruotsalainen, M. Moretti Sala
and 10 more authors
G. Monaco, P. Becker, Q. Faure, G. S. Thakur, M. Songvilay, C. Felser, P. H. M. van Loosdrecht, J. van den Brink, M. Hermanns, M. Grüninger
/ Abstract
The insulating mixed-valent Ir$^{+3.66}$ compound Ba$_4$NbIr$_3$O$_{12}$ hosts two holes per Ir$_3$O$_{12}$ trimer unit. We address the electronic structure via resonant inelastic x-ray scattering (RIXS) at the Ir $L_3$ edge and exact diagonalization. The holes occupy quasimolecular orbitals that are delocalized over a trimer. This gives rise to a rich intra-$t_{2g}$ excitation spectrum that extends from 0.5 eV to energies larger than 2 eV. Furthermore, it yields a strong modulation of the RIXS intensity as a function of the transferred momentum q. A clear fingerprint of the quasimolecular trimer character is the observation of two modulation periods, $2π/d$ and $2π/2d$, where d and 2d denote the intratrimer Ir-Ir distances. We discuss how the specific modulation reflects the character of the wavefunction of an excited state. Our quantitative analysis shows that spin-orbit coupling $λ$ of about 0.4 eV is decisive for the character of the electronic states, despite a large hopping $t_{a_{1g}}$ of about 0.8 eV. The ground state of a single trimer is described very well by both holes occupying the bonding j=1/2 orbital, forming a vanishing quasimolecular moment with J=0.