Local order and magnetic field effects on the electronic properties of disordered binary alloys in the Quantum Site Percolation limit

TL;DR

This paper introduces a new efficient method to study how local order and magnetic fields influence the electronic properties of disordered binary alloys, especially in the quantum percolation limit, revealing significant effects on the density of states.

Contribution

A novel approximate scheme that incorporates local order effects in finite geometries and predicts the density of states in disordered alloys under magnetic fields.

Findings

Magnetic fields cause band narrowing and gap formation near segregated regimes.

The effects of magnetic fields are periodic in flux and depend on local order.

Strong localization limits show minor magnetic field effects.

Abstract

Electronic properties of disordered binary alloys are studied via the calculation of the average Density of States (DOS) in two and three dimensions. We propose a new approximate scheme that allows for the inclusion of local order effects in finite geometries and extrapolates the behavior of infinite systems following `finite-size scaling' ideas. We particularly investigate the limit of the Quantum Site Percolation regime described by a tight-binding Hamiltonian. This limit was chosen to probe the role of short range order (SRO) properties under extreme conditions. The method is numerically highly efficient and asymptotically exact in important limits, predicting the correct DOS structure as a function of the SRO parameters. Magnetic field effects can also be included in our model to study the interplay of local order and the shifted quantum interference driven by the field. The average DOS is highly sensitive to changes in the SRO properties, and striking effects are observed when a magnetic field is applied near the segregated regime. The new effects observed are twofold: there is a reduction of the band width and the formation of a gap in the middle of the band, both as a consequence of destructive interference of electronic paths and the loss of coherence for particular values of the magnetic field. The above phenomena are periodic in the magnetic flux. For other limits that imply strong localization, the magnetic field produces minor changes in the structure of the average DOS.