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# Mott physics and band topology in materials with strong spin–orbit interaction

## Abstract

Recent theory and experiment have revealed that strong spin–orbit coupling can have marked qualitative effects on the band structure of weakly interacting solids, leading to a distinct phase of matter, the topological band insulator. We show that spin–orbit interaction also has quantitative and qualitative effects on the correlation-driven Mott insulator transition. Taking Ir-based pyrochlores as a specific example, we predict that for weak electron–electron interaction Ir electrons are in metallic and topological band insulator phases at weak and strong spin–orbit interaction, respectively. We show that by increasing the electron–electron interaction strength, the effects of spin–orbit coupling are enhanced. With increasing interactions, the topological band insulator is transformed into a ‘topological Mott insulator’ phase having gapless surface spin-only excitations. The proposed phase diagram also includes a region of gapless Mott insulator with a spinon Fermi surface, and a magnetically ordered state at still larger electron–electron interaction.

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## Acknowledgements

This work was supported by the DOE through Basic Energy Sciences grants DE-FG02-08ER46524 (L.B.) and DEFG02-07ER46452 (D.P.). The research facilities at the KITP were supported by the National Science Foundation grant NSF PHY-0551164.

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All authors contributed equally to this work.

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Correspondence to Dmytro Pesin.

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The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

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Pesin, D., Balents, L. Mott physics and band topology in materials with strong spin–orbit interaction. Nature Phys 6, 376–381 (2010). https://doi.org/10.1038/nphys1606

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• DOI: https://doi.org/10.1038/nphys1606

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