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Register a new userEnhanced spin-orbit coupling and orbital moment in ferromagnets by electron correlations
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In atomic physics, the Hund rule says that the largest spin and orbital state is realized due to the interplay of the spin-orbit coupling (SOC) and the Coulomb interactions. Here, we show that in ferromagnetic solids the effective SOC and the orbital magnetic moment can be dramatically enhanced by a factor of $1/[1-(2U^prime-U-J_H)rho_0]$, where $U$ and $U^prime$ are the on-site Coulomb interaction within the same oribtals and between different orbitals, respectively, $J_H$ is the Hund coupling, and $rho_0$ is the average density of states. This factor is obtained by using the two-orbital as well as five-orbital Hubbard models with SOC. We also find that the spin polarization is more favorable than the orbital polarization, being consistent with experimental observations. This present work provides a fundamental basis for understanding the enhancements of SOC and orbital moment by Coulomb interactions in ferromagnets, which would have wide applications in spintronics.
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Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a novel platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3 (3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report on a tunable and enhanced interface-induced Rashba spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3 bilayer with change in the underlying magnetic order of LaMnO3. We also observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals the quantitative valence of Mn and their impact on charge transfer. Further, we performed angle-dependent magnetoresistance measurements, which show signatures of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of LaMnO3. Our work thus demonstrates a new route to engineer the interface induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide interfaces which makes SrIrO3 an ideal candidate for spintronics applications.
Using ab initio calculations, we have investigated an insulating tetragonally distorted perovskite BaCrO$_3$ with a formal $3d^2$ configuration, the volume of which is apparently substantially enhanced by a strain due to SrTiO$_3$ substrate. Inclusion of both correlation and spin-orbit coupling (SOC) effects leads to a metal-insulator transition and in-plane zigzag orbital-ordering (OO) of alternating singly filled $d_{xz}+id_{yz}$ and $d_{xz}-id_{yz}$ orbitals, which results in a large orbital moment $M_L$ ~ -0.78 $mu_B$ antialigned to the spin moment $M_S$ ~ $2|M_L|$ in Cr ions. Remarkably, this ordering also induces a considerable $M_L$ for apical oxygens. Our findings show metal-insulator and OO transitions, driven by an interplay among strain, correlation, and SOC, which is uncommon in 3d systems.
We present a study of the paramagnetic metallic and insulating phases of vanadium sesquioxide by means of the $N$th order muffin-tin orbital implementation of density functional theory combined with dynamical mean-field theory. The transition is shown to be driven by a correlation-induced enhancement of the crystal field splitting within the $t_{2g}$ manifold, which results in a suppression of the hybridization between the $a_{1g}$ and $e_g^{pi}$ bands. We discuss the changes in the effective quasi-particle band structure caused by the correlations and the corresponding self-energies. At temperatures of about 400 K we find the $a_{1g}$ orbitals to display coherent quasi-particle behavior, while a large imaginary part of the self-energy and broad features in the spectral function indicate that the $e_g^{pi}$ orbitals are still far above their coherence temperature. The local spectral functions are in excellent agreement with recent bulk sensitive photoemission data. Finally, we also make a prediction for angle-resolved photoemission experiments by calculating momentum-resolved spectral functions.
We have uncovered a giant gyrotropic magneto-optical response for doped ferromagnetic manganite La2/3Ca1/3MnO3 around the near room-temperature paramagnetic-to-ferromagnetic transition. At odds with current wisdom, where this response is usually assumed to be fundamentally fixed by the electronic band structure, we point to the presence of small polarons as the driving force for this unexpected phenomenon. We explain the observed properties by the intricate interplay of mobility, Jahn-Teller effect and spin-orbit coupling of small polarons. As magnetic polarons are ubiquitously inherent to many strongly correlated systems, our results provide an original, general pathway towards the generation of gigantic gyrotropic responses that can be harnessed for nonreciprocal devices that exploit the polarization of light.
We investigate the interplay of spin-orbit coupling (SOC) and electronic correlations in Sr2RuO4 using dynamical mean-field theory. We find that SOC does not affect the correlation-induced renormalizations, which validates the Hunds metal picture of ruthenates even in the presence of the sizable SOC relevant to these materials. Nonetheless, SOC found to change significantly the electronic structure at k-points where a degeneracy applies in its absence. We explain why these two observations are consistent with one another and calculate effects of SOC on the correlated electronic structure. The magnitude of these effects is found to depend on the energy of the quasiparticle state under consideration, leading us to introduce the notion of an energy-dependent quasiparticle spin-orbit coupling. This notion is generally applicable to all materials in which both the spin-orbit coupling and electronic correlations are sizable.
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