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# Thermal chiral anomaly in the magnetic-field-induced ideal Weyl phase of Bi1−xSbx

## Abstract

The chiral anomaly is the predicted breakdown of chiral symmetry in a Weyl semimetal with monopoles of opposite chirality when an electric field is applied parallel to a magnetic field. It occurs because of charge pumping between monopoles of opposite chirality. Experimental observation of this fundamental effect is plagued by concerns about the current pathways. Here we demonstrate the thermal chiral anomaly, energy pumping between monopoles, in topological insulator bismuth–antimony alloys driven into an ideal Weyl semimetal state by a Zeeman field, with the chemical potential pinned at the Weyl points and in the absence of any trivial Fermi surface pockets. The experimental signature is a large enhancement of the thermal conductivity in an applied magnetic field parallel to the thermal gradient. This work demonstrates both pumping of energy and charge between the two Weyl points of opposite chirality and that they are related by the Wiedemann–Franz law.

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## Data availability

The data generated and analysed in this study are available within the paper and its Supplementary Information. Further data are available from the corresponding author on reasonable request.

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## Acknowledgements

This work was supported by CEM and NSF MRSEC under grant numbers DMR-2011876 (to D.V., W.Z., N.T., J.P.H.) and DMR-1420451 (all authors). The authors acknowledge useful discussions with M. A. H. Vozmediano. R. Ripley edited the text and contributed to the illustrations.

## Author information

Authors

### Contributions

The experiments were designed and carried out by D.V. and J.P.H. The theory was carried out by W.Z., C.Ş., M.E.F., N.T. and J.P.H. All contributed to the integration of theory and experiment and in writing the manuscript.

### Corresponding author

Correspondence to Joseph P. Heremans.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Peer review information Nature Materials thanks Kamran Behnia, Qiang Li, Binghai Yan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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## Supplementary information

### Supplementary Information

Supplementary figures and tables.

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Vu, D., Zhang, W., Şahin, C. et al. Thermal chiral anomaly in the magnetic-field-induced ideal Weyl phase of Bi1−xSbx. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-00983-8