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# Anomalous thermal transport under high pressure in boron arsenide

## Abstract

High pressure represents extreme environments and provides opportunities for materials discovery1,2,3,4,5,6,7,8. Thermal transport under high hydrostatic pressure has been investigated for more than 100 years and all measurements of crystals so far have indicated a monotonically increasing lattice thermal conductivity. Here we report in situ thermal transport measurements in the newly discovered semiconductor crystal boron arsenide, and observe an anomalous pressure dependence of the thermal conductivity. We use ultrafast optics, Raman spectroscopy and inelastic X-ray scattering measurements to examine the phonon bandstructure evolution of the optical and acoustic branches, as well as thermal conductivity under varied temperatures and pressures up to 32 gigapascals. Using atomistic theory, we attribute the anomalous high-pressure behaviour to competitive heat conduction channels from interactive high-order anharmonicity physics inherent to the unique phonon bandstructure. Our study verifies ab initio theory calculations and we show that the phonon dynamics—resulting from competing three-phonon and four-phonon scattering processes—are beyond those expected from classical models and seen in common materials. This work uses high-pressure spectroscopy combined with atomistic theory as a powerful approach to probe complex phonon physics and provide fundamental insights for understanding microscopic energy transport in materials of extreme properties.

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## Data availability

The data that support the plots within this paper and findings of this study are available from the corresponding author upon request.

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## Acknowledgements

We thank B. Kalkan, K. Armstrong and B. Lavina for technical help and discussion. Y.H. acknowledges support from a CAREER Award from the National Science Foundation (NSF) under grant no. DMR-1753393, an Alfred P. Sloan Research Fellowship under grant no. FG-2019-11788, and the Vernroy Makoto Watanabe Excellence in Research Award. This work used computational and storage services associated with the Hoffman 2 Shared Cluster provided by UCLA Institute for Digital Research and Education’s Research Technology Group, and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. This research used resources at the US Department of Energy (DOE) Office of Science user facility, including the Advanced Photon Source by Argonne National Laboratory under contract no. DE-AC02-06CH11357 and the Advanced Light Source by Lawrence Berkeley National Laboratory under contract no. DE-AC02-05CH1123.

## Author information

Authors

### Contributions

Y.H. proposed and directed the research. S.L., Z.Q. and M.L. performed the experiments. H.W. performed the theory calculations. M.K. helped with the XRD study. A.A. helped with the IXS study. A.K. helped with technical discussions. The manuscript was prepared by S.L., Z.Q., H.W., M.L. and Y.H. with input from all co-authors.

### Corresponding author

Correspondence to Yongjie Hu.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

## Peer review

### Peer review information

Nature thanks Yee Kan Koh and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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## Extended data figures and tables

### Extended Data Fig. 1 Synchrotron X-ray diffraction (XRD) measurement of BAs and its pressure-dependent lattice constant.

a, Synchrotron XRD patterns of BAs measured at different pressures (~0–32.6 GPa), verifying the cubic phase of BAs under all high pressures without phase transition. b, Experimentally measured pressure-dependent lattice constant of BAs (circles), in comparison with the ab initio calculation (line).

### Extended Data Fig. 2 Synchrotron single-crystal X-ray diffraction measurement.

Example diffraction image of BAs in which all peaks are indexed to the cubic phase.

### Extended Data Fig. 3 Inelastic X-ray scattering (IXS) spectrum measurement of BAs crystal.

Shown in figure are scattering peaks that determine the phonon frequency for scattering vector Q at (3.5 2.5 2.5).

### Extended Data Fig. 4 Brillouin scattering oscillation signals measured on a BAs sample.

Fast Fourier transform result of Brillouin scattering data (inset) determines the Brillouin frequency.

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Li, S., Qin, Z., Wu, H. et al. Anomalous thermal transport under high pressure in boron arsenide. Nature 612, 459–464 (2022). https://doi.org/10.1038/s41586-022-05381-x

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