Strong spin–orbit coupling is an essential ingredient of topological insulators and several other exotic electronic states, but it's not clear what happens in systems that have both strong spin–orbit coupling and strong electron–electron interactions. Boasting a combination of both ingredients, pyrochlore iridates may provide some insight.
Using photoemission techniques to image the electronic structure, Takeshi Kondo and colleagues found evidence for a node with a single point at the Fermi level of the pyrochlore iridate Pr2Ir2O7. With a quadratic dispersion and strong Coulomb interactions, this looks like a strongly correlated non-Fermi liquid version of mercury telluride quantum wells, which exhibit quantum spin Hall states.
What makes the observation fascinating is that we may be able to tune this material into a range of different states. Using a combination of alloying, hydrostatic pressure, strain and quantum confinement, this system could become an antiferromagnetic Weyl semimetal, a topological insulator or a quantum or anomalous spin Hall state. Kondo et al. may therefore have found a parent material for strongly interacting topological phases.
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Fleet, L. Call the tune. Nature Phys 12, 20 (2016). https://doi.org/10.1038/nphys3637
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DOI: https://doi.org/10.1038/nphys3637
