Multipolar magnetism in $5d^2$ vacancy-ordered halide double perovskites
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| Format: | Preprint |
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2024
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| _version_ | 1866914816202899456 |
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| author | Pradhan, Koushik Paramekanti, Arun Saha-Dasgupta, Tanusri |
| author_facet | Pradhan, Koushik Paramekanti, Arun Saha-Dasgupta, Tanusri |
| contents | Vacancy-ordered halide double perovskites hosting 4d/5d transition metals have emerged as a distinct platform for investigating unconventional magnetism arising out of the interplay of strong atomic spin-orbit coupling (SOC) and Coulomb interactions. Focusing on the $d^2$ system Cs$_2$WCl$_6$, our ab initio electronic structure calculation reveals very narrow electronic bands, fulfilling the necessary condition to realize exotic orders. Using this input, we solve the many-body spin-orbit coupled single-site problem by exact diagonalization and show that the multiplet structure of Cs$_2$WCl$_6$ hosts ground non-Kramers doublets on W, with vanishing dipole moment and a small gap to an excited magnetic triplet. Our work provides the rationale for the observed strong deviation from the classic Kotani behaviour in Cs$_2$WCl$_6$ for the measured temperature dependence of the magnetic moment. The non-Kramers doublets on W exhibit non-zero quadrupolar and octupolar moments, and our calculated two-site exchange supports the dominance of inter-site octupolar exchange over quadrupolar interactions. We predict ferro-octupolar order with a transition temperature $T_c \sim 5$K which may get somewhat suppressed by quantum fluctuations and disorder; this could be tested in future low-temperature experiments. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2403_05633 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Multipolar magnetism in $5d^2$ vacancy-ordered halide double perovskites Pradhan, Koushik Paramekanti, Arun Saha-Dasgupta, Tanusri Strongly Correlated Electrons Vacancy-ordered halide double perovskites hosting 4d/5d transition metals have emerged as a distinct platform for investigating unconventional magnetism arising out of the interplay of strong atomic spin-orbit coupling (SOC) and Coulomb interactions. Focusing on the $d^2$ system Cs$_2$WCl$_6$, our ab initio electronic structure calculation reveals very narrow electronic bands, fulfilling the necessary condition to realize exotic orders. Using this input, we solve the many-body spin-orbit coupled single-site problem by exact diagonalization and show that the multiplet structure of Cs$_2$WCl$_6$ hosts ground non-Kramers doublets on W, with vanishing dipole moment and a small gap to an excited magnetic triplet. Our work provides the rationale for the observed strong deviation from the classic Kotani behaviour in Cs$_2$WCl$_6$ for the measured temperature dependence of the magnetic moment. The non-Kramers doublets on W exhibit non-zero quadrupolar and octupolar moments, and our calculated two-site exchange supports the dominance of inter-site octupolar exchange over quadrupolar interactions. We predict ferro-octupolar order with a transition temperature $T_c \sim 5$K which may get somewhat suppressed by quantum fluctuations and disorder; this could be tested in future low-temperature experiments. |
| title | Multipolar magnetism in $5d^2$ vacancy-ordered halide double perovskites |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2403.05633 |