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Register a new userGiant Optical Polarization Rotation Induced by Spin-Orbit Coupling in Polarons
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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.
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Effects of the spin-orbit coupling (SOC) and magnetic field on excitonic insulating (EI) states are investigated. We introduce the two-orbital Hubbard model with the crystalline field splitting, which is a minimal model for discussing the exciton condensation in strongly correlated electron systems, and analyze its effective Hamiltonian in the strong correlation limit by using the mean-field theory. In the absence of the SOC and magnetic field, the ground state changes from the nonmagnetic band-insulating state to the EI state by increasing the Hund coupling. In an applied magnetic field, the magnetic moment appears in the EI state, which is continuously connected to the forced ferromagnetic state. On the other hand, in the presence of the SOC, they are separated by a phase boundary. We find that the magnetic susceptibility is strongly enhanced in the EI phase near the boundary with a small SOC. This peculiar behavior is attributed to the low-energy fluctuation of the spin nematicity inherent in the high-spin local state stabilized by the Hund coupling. The present study not only reveals the impact of the SOC for the EI state but also sheds light on the role of quantum fluctuations of the spin nematicity for the EI state.
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.
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.
We demonstrate an enhancement of the spin-orbit coupling in silicon (Si) thin films by doping with bismuth (Bi), a heavy metal, using ion implantation. Quantum corrections to conductance at low temperature in phosphorous-doped Si before and after Bi implantation is measured to probe the increase of the spin-orbit coupling, and a clear modification of magnetoconductance signals is observed: Bi doping changes magnetoconductance from weak localization to the crossover between weak localization and weak antilocalization. The elastic diffusion length, phase coherence length and spin-orbit coupling length in Si with and without Bi implantation are estimated, and the spin-orbit coupling length after the Bi doping becomes the same order of magnitude (Lso = 54 nm) with the phase coherence length (L{phi} = 35 nm) at 2 K. This is an experimental proof that the spin-orbit coupling strength in Si thin film is tunable by doping with heavy metals.
We report magnetotransport properties of BaZnBi$_{2}$ single crystals. Whereas electronic structure features Dirac states, such states are removed from the Fermi level by spin-orbit coupling (SOC) and consequently electronic transport is dominated by the small hole and electron pockets. Our results are consistent with three dimensional (3D) but also with quasi two dimensional (2D) portions of the Fermi surface. The spin-orbit coupling-induced gap in Dirac states is much larger when compared to isostructural SrMnBi$_{2}$. This suggests that not only long range magnetic order but also mass of the alkaline earth atoms A in ABX$_{2}$ (A = alkaine earth, B = transition metal and X=Bi/Sb) are important for the presence of low-energy states obeying the relativistic Dirac equation at the Fermi surface
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