Impact of a Jahn-Teller-like correlation coupling on the properties of mixed-valent ${\mathrm{SmB}}_6$

In previous studies a new type of Jahn-Teller coupling in doped ${\mathrm{SmB}}_6$ was presented both in a molecular and in an extended semiconductor model. The conventional role of configurational distortions is taken over by a symmetry-adapted electronic-correlation coupling, which takes advantage of the electronic properties of the host crystal. Within this model electron spin-resonance measurements of the systems ${\mathrm{SmB}}_6{:\mathrm{G}\mathrm{d}}^{3+}$ and ${\mathrm{SmB}}_6{:\mathrm{E}\mathrm{r}}^{3+}$ can be explained in a natural way. In this paper we examine the impact of this coupling-type on the properties of the band states. This results in a strong “softening” of the band states at the edge of the semiconducting gap and a contribution to the specific heat, which could serve as an additional experimental proof for the unconventional mechanism.