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Interpretation of Ir L-edge isotropic x-ray absorption spectra across the pressure-induced dimerization transition in hyper-honeycomb beta-Li2IrO3

Journal Article · · Physical Review, B: Condensed Matter
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The extended nature of atomic 5d orbitals, together with a relatively short ~ 3 °A Ir-Ir distance across edge-shared octahedra in honeycomb iridate lattices, leads to a tendency to disrupt the local, spin-orbit entangled jeff = 1 2 moments of Ir4+ ions in favor of dimerization and formation of molecular orbitals, especially upon lattice compression. The sensitivity of Ir L-edge spectroscopy to both spin-orbit entanglement in jeff states and quenching of orbital degrees of freedom in dimerized states, results in a peculiar evolution of x-ray absorption spectra across dimerization transitions including energy shifts in opposite direction for L3 and L2 leading absorption edges, and substantial changes in their isotropic branching ratio. We present a theoretical description of the evolution of 5d electronic states, and related x-ray absorption spectra, in going from the single ion to the dimerized limit. The calculations reproduce the experimental results for hyper-honeycomb β-Li2IrO3[1, 2] and shed light into the weakening of the coupling between spin and orbital degrees of freedom as the strength of dimerization increases. The results provide a basis for interpretation of L-edge xray absorption spectra in 5d systems where competition between formation of local jeff states and molecular orbitals is at play.

Research Organization:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
DOE Contract Number:
AC02-06CH11357
OSTI ID:
1910040
Journal Information:
Physical Review, B: Condensed Matter, Vol. 105, Issue 21
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English

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