Half metals at intermediate energy scales in Anderson-type insulators

TL;DR

This study reveals that spin polarization does not influence Anderson metal-insulator transitions with long-range Coulomb interactions, but magnetism affects transitions with local Hubbard interactions, leading to the emergence of half metals at intermediate energy scales.

Contribution

It demonstrates the existence of spin-dependent universality classes and the formation of half metals at intermediate energy scales in Anderson insulators.

Findings

Spin polarization is unrelated to Anderson transitions with Coulomb interactions.

Magnetism influences transitions with Hubbard interactions.

Half metals appear at intermediate energy scales, with only one spin species delocalized.

Abstract

Although quantum phase transitions involved with Anderson localization had been investigated for more than a half century, the role of spin polarization in these metal-insulator transitions has not been clearly addressed as a function of both the range of interactions and energy scales. Based on the Anderson-Hartree-Fock study, we reveal that the spin polarization has nothing to do with Anderson metal-insulator transitions in three dimensions as far as effective interactions between electrons are long-ranged Coulomb type. On the other hand, we find that metal-insulator transitions appear with magnetism in the case of Hubbard-type local interactions. In particular, we show that the multifractal spectrum of spin $\uparrow$ electrons differs from that of spin $\downarrow$ at the high-energy mobility edge, which indicates the existence of spin-dependent universality classes for metal-insulator transitions. One of the most fascinating and rather unexpected results is the appearance of half metals at intermediate energy scales above the high-energy mobility edge in Anderson-type insulators of the Fermi energy, that is, only spin $\uparrow$ electrons are delocalized while spin $\downarrow$ electrons are Anderson-type localized.