Electronic Properties of Metals and Semiconductors
The behaviour of electrons in a solid or liquid is the microscopic basis for chemistry and for most of the physical properties of solids and surfaces. This behaviour is being investigated in terms of quantum-theory. Experimentally-observed properties will be related and explained, and predictions for new features are already being made. Basic methods involve density-functional computer calculations. See also our Korringa-Kohn-Rostoker (KKR) activity.
Electronic Density near Defect
The charge-density, or density of electrons in a solid, is a function of only three spatial coordinates. From this function, the electronic ground-state energy can be calculated, and consequently the positions of all atoms in the solid and the forces between them. We show here the depletion of charge-density around a so-called "V" vacancy in silicon (density ''rho'' within a (110)-plane).(H. Hoehler, P.H. Dederichs).
Adatoms of As on a Silicon-Surface
Computer calculations by pseudopotential methods allow us to calculate atomistic details of semiconductor surfaces. We show here the cloud of electrons around the ionic cores of a silicon crystal covered with an As-layer (Si-111 surface).
(A.Antons, S. Bluegel, K. Schroeder; U. Funk-Kath, M. Boltes, Hel. Schumacher).
Complex Band Structure and Tunneling through Insulators
We are investigating the importance of metal-induced gap states for the tunneling of metal electrons through insulator films. By introducing an imaginary part to the wave vector in order to describe the decay of the wave function in the insulator, we obtain the complex band structure in the gap region. The spectrum of the decay parameters is calculated for the semiconductors Si, Ge, GaAs, and ZnSe. In most cases, for large enough film thicknesses, the tunneling is dominated by states of normal incidence on the interface; possible exceptions are considered. Based on our conclusions, we discuss the spin-dependent tunneling in Fe/Semiconductor/Fe (001) junctions.
(Mavropoulos M.; Papanikolaou N.; Dederichs P.H.; Complex Bandstructure and Tunneling through Ferromagnet/ Insulator/ Ferromagnet Junctions, Phys. Rev. Lett. 85, 1088 (2000).
"Hot Spots" in Tunneling Magnetoresistance
Ab initio calculations of the tunneling magnetoresistance show spectacular spikes in the k-parallel-resolved conductance, as indicated here for the conductance of a Co|Vacuum|Co junction with parallel aligned moments. The majority of electrons tunnel through the barrier in the same way as free electrons with a maximum transmission at the Gamma-bar point (e.g. perpendicular incidence on the barrier). However, for discrete k-parallel-values, identical to the occurrence of interface states, minority electrons can transverse the barrier without any attenuation. The origin and the behaviour of these "hot spots" are explained in detail by means of a simple analytical model and by ab initio calculations.
(O. Wunnicke, N. Papanikolaou, R. Zeller, P.H. Dederichs, V. Drchal, and J. Kudrnovsky: Effects of Resonant Interface States on Tunneling Magnetoresistance, submitted to Phys. Rev. Lett.).