Neutron spectroscopy and strongly correlated electrons: a view from the inside

Intermediate-valence state of the Sm and Eu in SmB6and EuCu2Si2: neutron spectroscopy data and analysis

“…Figure 1(a) shows that an increase in hybridization leads to a shift of the energetically favorable average valence towards the configuration f 6 corresponding to Eu 3+ . This approach was confirmed by the results of the measurements of the width of the quasielastic peak [11] as a function of the valence (and the Si concentration, respectively) shown in figure 3. As the system moves from the state 2+ to the state 3+, there is a significant increase in the width of the quasielastic peak.…”

“…(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016). A significant number of these results, especially for samarium systems, have been summarized in recent reviews [11,49]. Therefore, we focus here only on the results that are essential for the analysis of the specific features of systems based on Sm and Eu including some new recent data.…”

“…The two neighbours in the RE series, Sm 2+ and Eu 3+ , have the f 6 configuration. Many similarities have been discovered in the f-electron excitation spectra for Sm and Eu [11], particularly the influence of the valence change on the spectral parameters. Along with this, some difference was observed in the influence of external factors on the average valence that characterizes the IV state.…”

“…Such development allowed kinetic and thermodynamic properties of SmS and SmB 6 [8] to be described in frame of the intermediateradius exciton model. Spectroscopic methods, mainly inelastic neutron scattering (INS), are usually considered as the most effective in the studies of the intermediate-valence state due to its dynamical nature [9][10][11]. The INS technique provides incisive information about the dynamical magnetic susceptibility and allows a quantitative comparison with the above-mentioned models of the electronic states of Ce-and Yb-based systems, e.g.…”

“…The model of the 'intermediate-radius exciton' [7,8] pretends to be the most appropriate for the case of samarium (Sm(Y)S, SmB 6 ). It provides a description of the electron excitation spectra [11] and atomic vibration spectra [35] based on the common approach (the cooperative effects discovered recently [36] have not been taken into account in the original model). New experimental data [37] for a form factor of the IV state of the Sm ion, together with the results of versatile spectroscopic studies of the system EuCu 2 (Si,Ge) 2 [32,38,39] and other 1-2-2 class Eu-based systems (in particular, EuPd 2 Si 2 [40] and EuNi 2 P 2 [27]) serve as the experimental basis for development of the common approach for the system under consideration: SmB 6 /Sm(Y)S and EuCu 2 (Si,Ge) 2 .…”