Signatures of Orbital Order and Disorder in Fluoro-Perovskites with $t_{2g}$ Electronic Degeneracies
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arXiv
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| Autori principali: | , , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866909565169172480 |
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| author | Crawford, C. A. Hiley, C. I. Gainza, J. Ritter, C. Walton, R. I. Senn, Mark S. |
| author_facet | Crawford, C. A. Hiley, C. I. Gainza, J. Ritter, C. Walton, R. I. Senn, Mark S. |
| contents | A detailed high-resolution, variable temperature powder diffraction study of the fluoro-perovskites NaFeF$_3$ and NaCoF$_3$ is performed to probe their orbital ordering transitions. Through analysis of the symmetry adapted macrostrains and atomic distortions, we show that NaFeF$_3$ undergoes a C-type orbital order transition associated with the $t_{2g}^4$ states of Fe$^{2+}$. Counter-intuitively, the phase transition leading to the orbital order appears second order-like, which contradicts the thermodynamic requirements for electronic and isosymmeric phase transitions, implying that there must be an associated hidden symmetry breaking. On the other hand, for NaCoF$_3$, consideration of the symmetry adapted strains allows us to confidently rule out the occurrence of any long-range orbital orders down to 4 K. Since NaCoF$_3$ is an insulator with quenched orbital angular momentum at this temperature, our findings point towards a novel kind of orbital disorder associated to the $t_{2g}^5$ electronic degeneracy. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_03410 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Signatures of Orbital Order and Disorder in Fluoro-Perovskites with $t_{2g}$ Electronic Degeneracies Crawford, C. A. Hiley, C. I. Gainza, J. Ritter, C. Walton, R. I. Senn, Mark S. Strongly Correlated Electrons Materials Science A detailed high-resolution, variable temperature powder diffraction study of the fluoro-perovskites NaFeF$_3$ and NaCoF$_3$ is performed to probe their orbital ordering transitions. Through analysis of the symmetry adapted macrostrains and atomic distortions, we show that NaFeF$_3$ undergoes a C-type orbital order transition associated with the $t_{2g}^4$ states of Fe$^{2+}$. Counter-intuitively, the phase transition leading to the orbital order appears second order-like, which contradicts the thermodynamic requirements for electronic and isosymmeric phase transitions, implying that there must be an associated hidden symmetry breaking. On the other hand, for NaCoF$_3$, consideration of the symmetry adapted strains allows us to confidently rule out the occurrence of any long-range orbital orders down to 4 K. Since NaCoF$_3$ is an insulator with quenched orbital angular momentum at this temperature, our findings point towards a novel kind of orbital disorder associated to the $t_{2g}^5$ electronic degeneracy. |
| title | Signatures of Orbital Order and Disorder in Fluoro-Perovskites with $t_{2g}$ Electronic Degeneracies |
| topic | Strongly Correlated Electrons Materials Science |
| url | https://arxiv.org/abs/2504.03410 |