Temporal variations of valence states of the α-YbAl1−xFexB4 crystals (x = 0, 0.013, and 0.098) are experimentally examined in a nanosecond time-scale by time-resolved photoemission experiments using synchrotron radiation. The Yb 4f spectral features show no apparent change with time during relaxations after the optical pumping. The present experimental result indicates that dynamics of valence fluctuations in the material are likely dominated by a picosecond or much faster time-scale. The time-resolved measurement at the time-resolution limit at synchrotron radiation captured the trace of valence fluctuations.
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