The Theory Department of the "Max-Planck-Institut für Mikrostrukturphysik'' has started its activities in April 1998 and carries out theoretical research on the electronic, magnetic, optical, and electrical properties of micro- and nanostructured solid-state systems. More specifically, our research is currently focused on (i) exchange interactions in magnetic ultrathin films and nanostructures, (ii) magneto-electronics, i.e., spin-dependent electronic transport phenomena, and (iii) electron correlation spectroscopies of solid surfaces.

Exchange interactions

The exchange interaction is the "glue" which maintains the atomic magnetic moments parallel to each other in a ferromagnet. It is thus of primary importance for determining the magnetic excitations and, hence, the Curie temperature of ferromagnetic systems. It is rather well understood in bulk systems, but not in low-dimension systems such as ultrathin films and nanostructures. Our investigations are based upon first-principles electronic structure calculations, using the linear-muffin-tin-orbital (LMTO) method. These intensive numerical calculations are complemented by simple model studies which provide the basis for the physical understanding of the results.

Magneto-electronics

Magneto-electronics is an emerging field of science and technology in which the spin-dependent electronic transport properties of micro- and nanostructured solid state systems are studied and used to create new devices. Among the potential technological applications of magneto-electronics, let us just mention the realization of non-volatile magnetic random access memories (MRAM). Our research in this field is concerned with the tunneling magneto-resistance in ferromagnet/insulator/ferromagnet systems, with the extraordinary Hall effect of ultrathin magnetic multilayers, with spin-dependent transport phenomena in a two-dimensional electron gas such as the Rashba effect, and with magnetic scanning tunneling microscopy. Our approach relies on analytical and numerical calculations on simplified models, form which we obtain some insight on the physical mechanisms involved. In particular we investigate the role of disorder, and of spin-mixing due to spin-orbit scattering and magnetic impurity scattering.

Electron coincidence spectroscopies

Electron coincidence spectroscopies such as e-2e spectroscopy and double photo-emission have been recently successfully performed on solid state surfaces in our Institute. In contrast to single-electron spectroscopies, these new techniques yield some information on electronic pair correlations in the solid. We are developing theoretical and computational methods in order to investigate the physical mechanism of double emission processes and to interpret the electron coincidence experiments.
P. Bruno