Spin-Orbit Coupling and Interband Transitions in the Optical Conductivity of Sr_{2}RhO_{4}

Spin-Orbit Excitons in a Correlated Metal: Raman Scattering Study of Sr_{2}RhO_{4}

Using Raman spectroscopy to study the correlated 4d-electron metal Sr_{2}RhO_{4}, we observe pronounced excitations at 220 meV and 240 meV with A_{1g} and B_{1g} symmetries, respectively. We identify them as transitions between the spin-orbit multiplets of the Rh ions, in close analogy to the spin-orbit excitons in the Mott insulators Sr_{2}IrO_{4} and α-RuCl_{3}. This observation provides direct evidence for the unquenched spin-orbit coupling in Sr_{2}RhO_{4}. A quantitative analysis of the data reveals that the tetragonal crystal field Δ in Sr_{2}RhO_{4} has a sign opposite to that in insulating Sr_{2}IrO_{4}, which enhances the planar xy orbital character of the effective J=1/2 wave function. This supports a metallic ground state, and suggests that c-axis compression of Sr_{2}RhO_{4} may transform it into a quasi-two-dimensional antiferromagnetic insulator.

Enhanced magnetism and persistent insulating state in Mn doped Sr2IrO4

The influences of Mn substitution at the Ir site of Sr₂IrO₄are investigated via a comprehensive study of the variation of structural parameters, the transport and magnetic properties of the Sr₂Ir_1-xMn_xO₄samples. The incorporation of Mn leads to an increase of the in-plane Ir-O-Ir bond angle, while it is not sufficient to drive the Mott-insulating state to a metallic state. Interestingly, we find a coexistence of Ir⁴⁺-O^2--Ir⁴⁺super-exchange interaction and Mn³⁺-O^2--Mn⁴⁺double exchange interaction inx⩾ 0.06 samples. The Mn³⁺-O^2--Mn⁴⁺ferromagnetic domains are isolated by the Ir⁴⁺-O^2--Ir⁴⁺antiferromagnetic areas, leading to a severely localized electronic and magnetic states. The electron hopping between the localized states dominates the conductivity of the Sr₂Ir_1-xMn_xO₄samples.

Magnetization-Induced Band Shift in Ferromagnetic Weyl Semimetal Co_{3}Sn_{2}S_{2}

The discovery of magnetic Weyl semimetal (magnetic WSM) in Co_{3}Sn_{2}S_{2} has triggered great interest for abundant fascinating phenomena induced by band topology conspiring with the magnetism. Understanding how the magnetization affects the band structure can give us a deeper comprehension of the magnetic WSMs and guide us for the innovation in applications. Here, we systematically study the temperature-dependent optical spectra of ferromagnetic WSM Co_{3}Sn_{2}S_{2} experimentally and simulated by first-principles calculations. Our results indicate that the many-body correlation effect due to Co 3d electrons leads to the renormalization of electronic kinetic energy by a factor about 0.43, which is moderate, and the description within density functional theory is suitable. As the temperature drops down, the magnetic phase transition happens, and the magnetization drives the band shift through exchange splitting. The optical spectra can well detect these changes, including the transitions sensitive and insensitive to the magnetization, and those from the bands around the Weyl nodes. The results support that, in magnetic WSM Co_{3}Sn_{2}S_{2}, the bands that contain Weyl nodes can be tuned by magnetization with temperature change.