We illustrate the structure and dynamics of electron states in amorphous Si. The nature of the states near the gap at zero temperature is discussed and especially the way the structure of the states changes for energies ranging from midgap into either band tail (Anderson transition). We then study the effect of lattice vibrations on the eigenstates, and find that electronic states near the opti...

We study cold atoms in an optical lattice with synthetic spin-orbit coupling in the Mott-insulator regime. We calculate the parameters of the corresponding tight-binding model using Peierls substitution and "localized Wannier states method" and derive the low-energy spin Hamiltonian for bosons and fermions. The spin Hamiltonian is a combination of Heisenberg model, quantum compass model and Dzy...

The coherent motion of electronic wave packets in the Wannier-Stark regime of extemally biased GaAs/AIxGal _xAs superlattices is investigated by a time-resolved electro-optic technique. As predicted by the semiclassical theory, electronic wave packets undergo Bloch oscillations. They are observed via anisotropie changes in the refractive index associated with a intraband polarization, which is ...

The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene...

The coherent excitation of excitonic and continuum Wannier-Stark states in a semiconductor superlattice with femtosecond laser pulses leads to a modulation of both the interband and the intraband polarization. The field dependence of the Bloch oscillation frequency of the nonlinear interband polarization is shown to differ strongly from that of the intraband polarization. We find that the obser...

We study fourfold rotation-invariant gapped topological systems with time-reversal symmetry in two and three dimensions (d=2, 3). We show that in both cases nontrivial topology is manifested by the presence of the (d-2)-dimensional edge states, existing at a point in 2D or along a line in 3D. For fermion systems without interaction, the bulk topological invariants are given in terms of the Wann...

The spinel cobalt oxide Co3O4 is a magnetic semiconductor containing cobalt ions in Co2+ and Co3+ oxidation states. We have studied the electronic, magnetic, and bonding properties of Co3O4 using density functional theory (DFT) at the Generalized Gradient Approximation (GGA), GGA+U, and PBE0 hybrid functional levels. The GGA correctly predicts Co3O4 to be a semiconductor but severely underestim...

Strong electronic correlations lead to rich phase diagrams of electronic and magnetic states for many transition-metal oxides. LaMnO3 is one of the prototype materials to study the resulting phenomena such as for example colossal magnetoresistance. The widely used local density approximation (LDA) to density functional theory (DFT) fails to correctly describe correlated-electron systems. Theref...

We present new abelian partial difference sets and amorphic group schemes of both Latin square type and negative Latin square type in certain abelian p-groups. Our method is to construct what we call pseudo-quadratic bent functions and use them in place of quadratic forms. We also discuss a connection between strongly regular bent functions and amorphic group schemes.