Pseudogap Formation in the Intermetallic Compounds(Fe1−xVx)

Abstract

Optical conductivity data of the intermetallic compounds (Fe1-xVx)3Al ( 0</=x</=0.33) reveal that their density of states around the Fermi energy ( E(F)) is strongly reduced as x is increased. In particular, Fe2VAl ( x = 0.33) has a deep, well-developed pseudogap of 0.1-0.2 eV at E(F) and a small density ( approximately 5x10(20) cm(-3)) of carriers, which is highly unusual for intermetallic compounds. It is shown that the pseudogap results from the band structure of Fe2VAl, rather than from temperature-dependent correlation effects. Based on the present results, we propose a simple model that consistently explains both the semiconductorlike transport and the metallic photoemission results previously observed for Fe2VAl.

Structure and magnetic order in Fe2+xV1−xAl

“…This was interpreted in terms of Kondo-insulating behaviour, analogous to the system FeSi [3,4]. In contrast, optical conductivity studies provided evidence for a pseudogap in the density of states of Fe 2 VAl of 0.1-0.2eV [5], a view supported by various band structure calculations [6][7][8]. Notably, no temperature dependence of the gap features has been detected in these studies, apparently contradicting a Kondo insulator scenario for Fe 2 VAl.…”

“…Finally, if the resistivity, as suggested in Ref. 5, largely arises from spin dependent scattering, then the very strong reduction of the resistivity in the slowly cooled sample rather indicates a reduction of disorder scattering, in conflict with a view of impurity induced ferromagnetism.…”

“…[5], because of the electron count Al deficiency might have a strong effect on the actual position of the Fermi level E F in a pseudogap system. Specifically, it was argued that Al deficiency moves E F out of the centre of the pseudogap into the slopes, implying that Al deficient material should be more metallic than non-deficient one.…”

“…Our structural investigation proves that slowly-cooled Fe 2 VAl, which we established on a microscopic scale to be ferromagnetically ordered below T C = 13K, is structurally better ordered than quenched material, for which we found evidence for substantial Al off-stoichiometry. For the quenched material the bulk properties [13] resemble the behaviour of "Kondo-insulating like" or "pseudogap" Fe 2 VAl [1,2,5,[9][10][11]16]; this suggests that the materials investigated in those works are Al deficient.As pointed out in Ref.[5], because of the electron count Al deficiency might have a strong effect on the actual position of the Fermi level E F in a pseudogap system. Specifically, it was argued that Al deficiency moves E F out of the centre of the pseudogap into the slopes, implying that Al deficient material should be more metallic than non-deficient one.…”

“…Therefore, in Ref. 5 it has been speculated that the (magneto)resistivity of Fe 2 VAl reflects a mixture of electron excitation processes over the pseudogap and spin dependent scattering from impurities.…”