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arXiv · 1712.10137

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

Yasuhiro Shimizu·Takuya Takahashi·Syunpei Yamada·Ayako Shimokata·Takaaki Jin-no·Masayuki Itoh
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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.

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Yasuhiro Shimizu, Takuya Takahashi, Syunpei Yamada, Ayako Shimokata, Takaaki Jin-no, Masayuki Itoh. 2017-12-29. Symmetry Preservation and Critical Fluctuations in a Pseudospin Crossover Perovskite LaCoO$_3$. https://doi.org/10.1103/physrevlett.119.267203

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