Electron-correlation euects in a disordered Fe2TiSn Heusler alloy

Recent electrical transport, specific heat and magnetic measurements indicated that the Heusler-type Fe2TiSn alloy could be a candidate for a 3d heavy-fermion system with a quasi-particle effective mass of similar to 40 times the free electron mass. Ab initio electronic structure calculations yield a nonmagnetic ground state with a pseudogap and a very small number of the density of states at the Fermi level. However, the atomic disorder strongly influences the magnetic and transport properties of Fe2TiSn samples. In contrast to the thermodynamical properties of Fe2TiSn, the infrared studies do not support the notion that the Kondo interaction plays a dominant role in this alloy and rather Support the interband transition across a pseudogap responsible for the mass enhancement. The many-body calculations, however, have shown that the narrow d band resulting from Fe/Ti site exchange (i.e. Fe impurity atoms) can be responsible for the unusual temperature dependences of the physical properties of the Fe2TiSn alloy. In this review paper we discuss the implications of our findings for the ground-state properties of Fe2TiSn, in particular with respect to the role of atomic disorder.