Abstract
Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, particularly on the formation of novel electronic states and manifested metal-insulator transitions (MITs). SOC plays a dominant role in 5d5 iridates (Ir4+), undergoing MITs both concurrent (pyrochlores) and separated (perovskites) from the onset of magnetic order. However, the role of SOC for other 5d configurations is less clear. For example, 5d3 (Os5+) systems are expected to have an orbital singlet with reduced effective SOC. The pyrochlore Cd2Os2O7 nonetheless exhibits a MIT entwined with magnetic order phenomenologically similar to pyrochlore iridates. Here, we resolve the magnetic structure in Cd2Os2O7 with neutron diffraction and then via resonant inelastic X-ray scattering determine the salient electronic and magnetic energy scales controlling the MIT. In particular, SOC plays a subtle role in creating the electronic ground state but drives the magnetic order and emergence of a multiple spin-flip magnetic excitation.
Highlights
Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, on the formation of novel electronic states and manifested metal-insulator transitions (MITs)
The specific type of magnetic structure adopted on the frustrated pyrochlore lattice is predicted to play a crucial role in the potential Weyl semi-metal state in the pyrochlore iridates and the magnetic MIT in Cd2Os2O7
The magnetic ground state in Cd2Os2O7 has been shown to be consistent with the AIAO ordering[8], as with the predictions of AIAO ordering on the pyrochlore iridates this relied on some conjecture on the basis of structural arguments
Summary
Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, on the formation of novel electronic states and manifested metal-insulator transitions (MITs). In 5d oxides the relativistic spin-orbit coupling (SOC) is increased to such an extent that competition occurs with the on-site electron correlations, as well as further interactions such as the crystalline electric field (CEF), Hund’s coupling and increased orbital overlap The consequence of these often finely balanced interactions in 5d oxides is the emergence of new physics, such as a SOC dominated jeff 1⁄4 1/2 Mott-like insulating state, initially observed in perovskite iridates[3,4], and Weyl semi-metal, non-trivial topological insulators and magnetic MITs in pyrochlore iridates[2,5,6]. Despite the distinct electronic ground states, the NPD and RIXS results on the 5d3-osmate Cd2Os2O7 indicate parallels with 5d5-iridate pyrochlores and the predictions of associated exotic topological insulating and Weyl semi-metal states
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