Nonmagnetic ground state, Crystal field effects and Heavy-fermion behaviour in the Remeika Phase: Pr$_3$Ir$_4$Ge$_{13}$

Abstract

We report the magnetic, electronic and transport properties of the quasi-skutterudite compound Pr 3 Ir 4 Ge 13 by means of magnetic susceptibility χ(T ), electrical resistivity ρ(T ), specific heat C p (T ), thermal conductivity κ(T ), thermoelectric power S(T ) and Hall coefficient R H (T ) measurements. Pr 3 Ir 4 Ge 13 does not show any phase transition down to 1.9 K. Magnetic, and specific measurements show that the system possesses a crystal electric field singlet ground state that is separated from the first excited state by about 37 K. ρ(T ) shows a negative temperature coefficient of resistance for the whole temperature range studied and which can be explained in terms of Mott's impurity band conduction mechanism. R H (T ) measurements show that Pr 3 Ir 4 Ge 13 is a low-carrier density semimetal and its transport properties indicate a metallic-non metallic cross over behaviour. Large Seebeck values were observed for the entire temperature range of investigation, and the analysis of temperature variation of S and S/T showed no sign of strong correlation between the Pr 4f 2 and conduction electron states near Fermi level. A large Sommerfeld coefficient, γ = 150 mJ/(mol K 2 ) indicates the formation of a moderate heavy-fermion state emerging from the dynamical crystal field fluctuations.