Symmetry Preservation and Critical Fluctuations in a Pseudospin Crossover Perovskite LaCoO${}_3$

Abstract

Spin-state crossover beyond a conventional ligand-field theory has been a fundamental issue in condensed matter physics. Here, we report microscopic observations of spin states and low-energy dynamics through orbital-resolved NMR spectroscopy in the prototype compound LaCoO${}_3$. The ${}^{59}$Co NMR spectrum shows the preserved crystal symmetry across the crossover, inconsistent with $d$ orbital ordering due to the Jahn-Teller distortion. The orbital degeneracy results in a pseudospin ($\tilde{J}=1$) excited state with an orbital moment observed as ${}^{59}$Co hyperfine coupling tensors. We found that the population of the excited state evolves above the heart crossover temperature. The crossover involves critical spin-state fluctuations emerging under the magnetic field. These results suggest that the spin-state crossover can be mapped into a statistical problem, analogous to the supercritical liquid in liquid-gas transition.

5 pages, 5 figures

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Cited by in corpus (1)

• Occupation switching of $d$ orbitals probed via hyperfine interactions in vanadium dioxide