Abstract
The silicon clathrates—materials composed of metal-doped Si20 dodecahedra—were identified as the first superconductors based on pure silicon networks1,2. The mechanism of superconductivity in these materials can be obtained by studying their phonon modes, as modified by isotope substitution, and specific-heat measurements. Here, we present experimental studies that provide strong evidence that superconductivity in Ba8Si46 is explained in the framework of phonon-mediated Bardeen–Cooper–Schriefer theory. Analyses using the McMillan approximation3,4 of the Eliashberg equation indicate that the superconducting mechanism is in the medium coupling regime, but at the high-end limit. The large density of states at the Fermi level, which arises from hybridization of the Si20 cluster and Ba orbitals, is responsible for the unexpectedly high superconducting temperature. The temperature evolution of the specific heat unambiguously shows that this is an s-wave symmetry superconductor.
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Acknowledgements
The authors thank V. I. Ozhogin for supplying 30Si and T. Atake for discussion of specific heat. We also wish to thank the staff members at SPring-8, Japan (beamline BL02B2 and BL25SU) for their support and to express our appreciation for the use of the facility of high-energy beam. Institute of Material Research No129-2003 is also acknowledged for support of its facility usage. Financial support from the nanotechnology proposals of the both beam lines from SPring-8 is also greatly appreciated. The project was supported by a Grant-in-Aid from the Ministry of Education, Sport, Science and Culture of Japan, No. 13304031 and 14076215. This work has been supported by PRESTO and CREST of JST (Japan Science and Technology Corporation).
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Tanigaki, K., Shimizu, T., Itoh, K. et al. Mechanism of superconductivity in the polyhedral-network compound Ba8Si46. Nature Mater 2, 653–655 (2003). https://doi.org/10.1038/nmat981
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DOI: https://doi.org/10.1038/nmat981
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