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# Hidden order in URu2Si2 originates from Fermi surface gapping induced by dynamic symmetry breaking

## Abstract

Spontaneous, collective ordering of electronic degrees of freedom leads to second-order phase transitions that are characterized by an order parameter driving the transition. The notion of a ‘hidden order’ has recently been used for a variety of materials where a clear phase transition occurs without a known order parameter. The prototype example is the heavy-fermion compound URu2Si2, where a mysterious hidden-order transition occurs at 17.5 K. For more than twenty years this system has been studied theoretically and experimentally without a firm grasp of the underlying physics. Here, we provide a microscopic explanation of the hidden order using density-functional theory calculations. We identify the Fermi surface ‘hot spots’ where degeneracy induces a Fermi surface instability and quantify how symmetry breaking lifts the degeneracy, causing a surprisingly large Fermi surface gapping. As the mechanism for the hidden order, we deduce spontaneous symmetry breaking through a dynamic mode of antiferromagnetic moment excitations.

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## Change history

• ### 26 February 2009

In the version of this article initially published online, the caption for Figure 2 was incorrect; it has now been corrected on all versions of the article.

## References

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## Acknowledgements

We acknowledge discussions with R. Caciuffo, M. Biasini, G. H. Lander, N. Bernhoeft, J. Flouquet, W. J. L. Buyers, J. D. Denlinger, J. W. Allen, H. Harima, P. Coleman, P. Chandra, M.-T. Suzuki and M. B. Maple. This work was supported by the Swedish Research Council (VR), the Swedish National Infrastructure for Computing (SNIC), STINT, COST P16 and the European Commission, JRC-ITU.

## Author information

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### Corresponding authors

Correspondence to S. Elgazzar or P. M. Oppeneer.

## Supplementary information

### Supplementary Information

Supplementary Information (PDF 436 kb)

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Elgazzar, S., Rusz, J., Amft, M. et al. Hidden order in URu2Si2 originates from Fermi surface gapping induced by dynamic symmetry breaking. Nature Mater 8, 337–341 (2009). https://doi.org/10.1038/nmat2395

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• DOI: https://doi.org/10.1038/nmat2395

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