Titus Sandu — Page 2

arXiv2006

Spin tunneling through an indirect barrier

Spin-dependent tunneling through an indirect bandgap barrier like the GaAs/AlAs/GaAs heterostructure along [001] direction is studied by the tight-binding method. The tunneling is characterized by the proportionality of the Dresselhaus Hamiltonians at $Γ$ and $X$ points in the barrier and by Fano resonances. The present results suggest that large spin polarization can be obtained for energy windows that exceed significantly the spin splitting. We also formulate two conditions that are necessary for the existence of energy windows with large polarization.

cond-mat.mtrl-sci↗

arXiv2005

Optical matrix elements in tight-binding models with overlap

We investigate the effect of orbital overlap on optical matrix elements in empirical tight-binding models. Empirical tight-binding models assume an orthogonal basis of (atomiclike) states and a diagonal coordinate operator which neglects the intra-atomic part. It is shown that, starting with an atomic basis which is not orthogonal, the orthogonalization process induces intra-atomic matrix elements of the coordinate operator and extends the range of the effective Hamiltonian. We analyze simple tight-binding models and show that non-orthogonality plays an important role in optical matrix elements. In addition, the procedure gives formal justification to the nearest-neighbor spin-orbit interaction introduced by Boykin [Phys. Rev \textbf{B} 57, 1620 (1998)] in order to describe the Dresselahaus term which is neglected in empirical tight-binding models.

cond-mat.mtrl-sci↗