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

摘要

Electronic properties of disordered binary alloys are studied via thecalculation of the average Density of States (DOS) in two and three dimensions.We propose a new approximate scheme that allows for the inclusion of localorder effects in finite geometries and extrapolates the behavior of infinitesystems following `finite-size scaling' ideas. We particularly investigate thelimit of the Quantum Site Percolation regime described by a tight-bindingHamiltonian. This limit was chosen to probe the role of short range order (SRO)properties under extreme conditions. The method is numerically highly efficientand asymptotically exact in important limits, predicting the correct DOSstructure as a function of the SRO parameters. Magnetic field effects can alsobe included in our model to study the interplay of local order and the shiftedquantum interference driven by the field. The average DOS is highly sensitiveto changes in the SRO properties, and striking effects are observed when amagnetic field is applied near the segregated regime. The new effects observedare twofold: there is a reduction of the band width and the formation of a gapin the middle of the band, both as a consequence of destructive interference ofelectronic paths and the loss of coherence for particular values of themagnetic field. The above phenomena are periodic in the magnetic flux. Forother limits that imply strong localization, the magnetic field produces minorchanges in the structure of the average DOS.