Drastic enhancement of electronic correlations induced by hydrogen insertion in the cerium intermetallic compound CeFeSi.

We report a comparative study of two cerium-based intermetallic compounds: CeFeSi with an anti-PbFCl type structure, and CeFeSiH with a ZrCuSiAs type structure. The latter is obtained from CeFeSi through hydrogen insertion. Our results are based on X-rays, transport, thermodynamic and magnetic measurements. While the tetragonal structure with P4/nmm symmetry remains unchanged after hydrogen insertion, the thermodynamic, magnetic, and transport properties change drastically. On the one hand, CeFeSi behaves as a Pauli paramagnet with a small Sommerfeld coefficient, indicating the absence of 4f electron physics. On the other hand, our study shows that CeFeSiH exhibits strong magnetic fluctuations with a magnetic transition at 3.5 K, and coherent Kondo-lattice heavy-fermion features.