Charge-density wave, superconductivity and -electron valence instability in EuBiSF
arXiv:1407.7132 · doi:10.1103/PhysRevB.90.064518
Abstract
Superconductivity (SC) and charge-density wave (CDW) are two contrasting yet relevant collective electronic states which have received sustained interest for decades. Here we report that, in a layered europium bismuth sulfofluoride, EuBiSF, a CDW-like transition occurs at 280 K, below which SC emerges at 0.3 K, without any extrinsic doping. The Eu ions were found to exhibit an anomalously temperature-independent mixed valence of about +2.2, associated with the formation of CDW. The mixed valence of Eu gives rise to self electron doping into the conduction bands mainly consisting of the in-plane Bi-6 states, which in turn brings about the CDW and SC. In particular, the electronic specific-heat coefficient is enhanced by ~ 50 times, owing to the significant hybridizations between Eu-4 and Bi-6 electrons, as verified by band-structure calculations. Thus, EuBiSF manifests itself as an unprecedented material that simultaneously accommodates SC, CDW and -electron valence instability.
10 pages, 6 figures
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