Strong valence fluctuation in the quantum critical heavy fermion superconductor β-YbAlB4: a hard x-ray photoemission study

Electronic structures of the quantum critical superconductor β-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence are estimated to be ∼2.73 and ∼2.75 for α- and β-YbAlB4, re...

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Bibliographic Details
Published in:Physical review letters 2010-06, Vol.104 (24), p.247201-247201
Main Authors: Okawa, M, Matsunami, M, Ishizaka, K, Eguchi, R, Taguchi, M, Chainani, A, Takata, Y, Yabashi, M, Tamasaku, K, Nishino, Y, Ishikawa, T, Kuga, K, Horie, N, Nakatsuji, S, Shin, S
Format: Article
Language:English
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Summary:Electronic structures of the quantum critical superconductor β-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence are estimated to be ∼2.73 and ∼2.75 for α- and β-YbAlB4, respectively, thus providing clear evidence for valence fluctuations. The valence band spectra of these compounds also show Yb2+ peaks at the Fermi level. These observations establish an unambiguous case of a strong mixed valence at quantum criticality for the first time among heavy fermion systems, calling for a novel scheme for a quantum critical model beyond the conventional Doniach picture in β-YbAlB4.
ISSN:1079-7114
DOI:10.1103/PhysRevLett.104.247201