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Spectroscopic evidence of a new energy scale for superconductivity in H3S

Matters Arising to this article was published on 11 August 2022

Abstract

The discovery of a superconducting phase in sulfur hydride under high pressure with a critical temperature above 200 K has provided fresh impetus to the search for superconductors at ever higher temperatures. Although this system displays all of the hallmarks of superconductivity, the mechanism through which it arises remains to be determined. Here we provide a first optical spectroscopy study of this superconductor. Experimental results for the optical reflectivity of H3S, under hydrostatic pressure of 150 GPa, for several temperatures and over the range 60 to 600 meV of photon energies, are compared with theoretical calculations based on Eliashberg theory. Two significant features stand out: some remarkably strong infrared-active phonons at around 160 meV, and a band with a depressed reflectance in the superconducting state in the region from 450 meV to 600 meV. In this energy range H3S becomes more reflecting with increasing temperature, a change that is traced to superconductivity originating from the electron–phonon interaction. The shape, magnitude and energy dependence of this band at 150 K agrees with our calculations. This provides strong evidence of a conventional mechanism. However, the unusually strong optical phonon suggests a contribution of electronic degrees of freedom.

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Figure 1: Theoretical reflectivity of H3S.
Figure 2: The superconducting gap of H3S.
Figure 3: The bosonic signature of H3S.
Figure 4: Phonon structures in the reflectance of H3S.
Figure 5: Diamond anvil cell.

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Acknowledgements

We thank P. Allen, D. Embury, I. Errea, F. Mauri, W. Pickett, A. Sanna and D. Tanner for helpful discussions. We also thank M. Deutsch, L. Manceron and M. Faye for useful discussions and for technical guidance. J.P.C., E.J.N. and T.T. were supported by the Natural Science and Engineering Research Council of Canada (NSERC). J.P.C. and T.T. received additional support from the Canadian Institute for Advanced Research (CIFAR). M.I.E. received financial support from the European Research Council 2010-Advanced Grant 267777. B.L. and F.C. received financial support from SOLEIL synchrotron. The high-pressure low-temperature set-up was developed through a grant from Region Centre.

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This project has been initiated and supervised by T.T., M.I.E. and P.R. Samples have been synthesized and characterized by A.D. and M.I.E. Infrared measurements and data treatment were carried out by B.L., F.C., J.-B.B., P.R. and T.T. The calculations were performed by E.J.N. and J.P.C. All authors contributed to the writing of the paper.

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Correspondence to P. Roy or T. Timusk.

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The authors declare no competing financial interests.

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Capitani, F., Langerome, B., Brubach, JB. et al. Spectroscopic evidence of a new energy scale for superconductivity in H3S. Nature Phys 13, 859–863 (2017). https://doi.org/10.1038/nphys4156

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