Thermodynamics of a Narrow-Band Bose Gas on a Lattice

In strong-coupling electron-lattice systems local pairs of electrons form—the so-called bipolarons. They behave like a Bose liquid on a lattice and have very small bandwidth $b$. We show that the specific heat for those bosons in the normal phase is extremely similar to that obtained for electrons in equivalently narrow bands: a behavior linear in $T$ for low temperature ($T<<t$) and a $T^{-2\mathrm{}}$ law for high temperature ($T>~t$). In contrast, the magnetic susceptibility for triplet bosons differs qualitatively from that of electrons in the low-temperature regime. We discuss those results in view of a possible application to compounds exhibiting heavy-mass carriers.