Magnon dressing by orbital excitations in ferromagnetic planes of K$_2$CuF$_4$ and LaMnO$_3$
| Autor: | Andrzej M. Oleś, Mateusz Snamina |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
Physics
Condensed Matter - Materials Science Condensed matter physics Strongly Correlated Electrons (cond-mat.str-el) Heisenberg model Magnon General Physics and Astronomy Materials Science (cond-mat.mtrl-sci) FOS: Physical sciences 01 natural sciences 010305 fluids & plasmas Brillouin zone Renormalization Condensed Matter - Strongly Correlated Electrons Excited state 0103 physical sciences Quasiparticle Condensed Matter::Strongly Correlated Electrons 010306 general physics Ground state Spin (physics) |
| DOI: | 10.48550/arxiv.1811.03372 |
| Popis: | We show that even when spins and orbitals disentangle in the ground state, spin excitations are renormalized by the local tuning of $e_g$ orbitals in ferromagnetic planes of K$_2$CuF$_4$ and LaMnO$_3$. As a result, dressed spin excitations (magnons) obtained within the electronic model propagate as quasiparticles and their energy renormalization depends on momentum ${\vec k}$. Therefore magnons in spin-orbital systems go beyond the paradigm of the effective Heisenberg model with nearest neighbor spin exchange derived from the ground state --- spin-orbital entanglement in excited states predicts large magnon softening at the Brillouin zone boundary, and in case of LaMnO$_3$ the magnon energy at the $M=(\pi,\pi)$ point may be reduced by $\sim 45$\%. In contrast, simultaneously the stiffness constant near the Goldstone mode is almost unaffected. We elucidate physics behind magnon renormalization in spin-orbital systems and explain why long wavelength magnons are unrenormalized while simultaneously energies of short wavelength magnons are reduced by orbital fluctuations. In fact, the ${\vec k}$-dependence of the magnon energy is modified mainly by dispersion which originates from spin exchange between second neighbors along the cubic axes $a$ and $b$. Comment: 15 pages, 4 figures, submitted |
| Databáze: | OpenAIRE |
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