High-Pressure and Low-Temperature Physics pp 141-168 | Cite as

# Theoretical Approach to the Configuration Fluctuation in Sm-Chalcogenides

## Abstract

We present a theoretical approach to the problem of configuration mixing in Sm chalcogenides. Properties in the collapsed phase of SmS are discussed in terms of an essentially localized or excitonic picture of most of the Sm 5d-electrons, with a small number (≃.1 electrons per Sm) occupying the free-electron-like states at the bottom of a broad 5d-band. We review how such an essentially localized model for the 5d-electrons can lead to the observed results on volume and degree of mixing vs. pressure, low-T specific heat, dc electrical conductivity, plasma frequency, XPS intensities and magnetism. We also present new calculations of phase boundaries in the T-p plane, obtaining for SmS both a first order and a second order boundary within a simplified model. The latter boundary, which occurs e.g. at high p and low T makes contact with a recent experimental result of Guntherodt et al. The unusual shape of the observed first-order boundary is shown to be in accord with our general model, A new evaluation of the low frequency dielectric constant (ħω⋝.lev) shows behavior very similar to the unusual experimental results obtained recently by Batlogg et al. and by Allen. We compare the above picture with the more common models where all the 5d-electrons (~.7 per Sm in SmS) occupy free-electron like states, and give a critique of the latter.

### Keywords

Entropy Nickel Shrinkage Hull Posite## Preview

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### References

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