Excitonic Correlations in the Intermetallic Fe2VAl

TL;DR

This paper investigates the complex electronic structure of Fe2VAl, revealing how excitonic correlations influence its unusual transport and magnetic properties, and assesses the likelihood of excitonic condensate formation.

Contribution

It provides a detailed analysis of Fe2VAl's band structure, effects of corrections, and evaluates excitonic phenomena, proposing a model based on low-density electron-hole interactions.

Findings

Carrier density reduced by spin-orbit coupling and GGA corrections.

Doping induces magnetic moments and destroys the pseudogap.

Excitonic condensate and Wigner crystal formation are unlikely.

Abstract

The intermetallic compound Fe2VAl looks non-metallic in transport and strongly metallic in thermodynamic and photoemission data. It has in its band structure a highly differentiated set of valence and conduction bands leading to a semimetallic system with a very low density of carriers. The pseudogap itself is due to interaction of Al states with the d orbitals of Fe and V, but the resulting carriers have little Al character. The effects of generalized gradient corrections to the local density band structure as well spin-orbit coupling are shown to be significant, reducing the carrier density by a factor of three. Doping of this nonmagnetic compound by 0.5 electrons per cell in a virtual crystal fashion results in a moment of 0.5 bohr magnetons and destroys the pseudogap. We assess the tendencies toward formation of an excitonic condensate and toward an excitonic Wigner crystal, and find both to be unlikely. We propose a model is which the observed properties result from excitonic correlations arising from two interpenetrating lattices of distinctive electrons (e_g on V) and holes (t_2g on Fe) of low density (one carrier of each sign per 350 formula units).