Pressure and temperature evolution of Sm mean-valence in golden SmS

We have performed Sm-L₃ edge x-ray absorption spectroscopy measurement of intermediate-valence (IV) compound SmS in high-resolution partial fluorescence yield mode (PFY-XAS) under pressure and low temperature. Incident energy dependence of the PFY intensity significantly changes at a critical pressure P_c1 where a valence transition occurs from divalent to IV state. In the pressure region of P > P_c1, in which a pseudogap opens, the Sm mean-valence slightly decreases with lowering temperature. When the pressure is increased above P_c2 where a magnetic ordering appears and the pseudogap disappears, the Sm mean-valence does not show clear variation with temperature. These results give us a new insight into the role of valence fluctuation in the pseudogap formation of SmS. (author)