Abstract
Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local point symmetry breaking or local spin expectation values, even in materials with simple cubic crystal structure such as Ba2NaOsO6. Experimental tests of these theories by local probes are highly sought for. Our local measurements designed to concurrently probe spin and orbital/lattice degrees of freedom of Ba2NaOsO6 provide such tests. Here we show that a canted ferromagnetic phase which is preceded by local point symmetry breaking is stabilized at low temperatures, as predicted by quantum theories involving multipolar spin interactions.
Highlights
Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research
This is important in so far that it clearly shows that quantum models based on complex multipolar interaction generating high-order spin exchange is consistent with the observed nature of emergent phases in Mott insulators with the strong SOC3,20
One structurally distinct Na site in non-cubic environment is generated. As it results from our calculations, distortions that generate orthorhombic local symmetry at the Na site are required to account for both the amplitude of the detected splitting and its dependence on the field orientation
Summary
Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Interesting is the case of materials with a double perovskites structure, for which it has been proposed that partial lifting of degeneracy of the total angular momentum eigenstates induces a highly nontrivial multipolar exchange interactions3,4 These peculiar interactions promote quantum fluctuations and generate novel quantum states impossible without strong SOC3,4,16. The most unusual observation is that the FM state easy axis is in the [110] direction, as this does not occur in standard Landau theory for ferromagnetism in a cubic symmetry3 This uncommon magnetism can either be explained by the density functional theory electronic structure calculations, that include effects of electron correlation, a strong SOC, and anisotropic exchange interaction; or, by quantum models including multipolar exchange interactions arising from strong SOC3,20. Experimental confirmation of the microscopic quantum models requires the observation of two effects These comprise a structural change, that precedes magnetic order, associated with the quadrupolar ordering and local spin expectation values, that differ from the average ones. Our findings establish that such quantum models represent an appropriate theoretical framework for predicting emergent properties in materials with both strong correlations and SOC, in general
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