Subject Area C2: Diffusive, Ballistic and Superconducting Transport in Hybrid Structures
Daniela Pfannkuche, Ulrich Merkt
Where does the current flow? This question is of particular importance in systems that are
composed of different constituents, for example metals and semiconductors.
In the diffusive range the conductivity is spatially varying and magnetic fields influence
the current paths. The current paths depend also on the geometry of the sample and the
positions of the current and voltage contacts. The redistribution of the current
leads to different magnetoresistance effects such as the extraordinary magnetoresistance
that is important for novel read-head technologies.
In hybrid systems that are made of extremely clean base materials the charge transport is
determined mainly by scattering from boundaries and interfaces. In this ballistic range
an applied voltage may lead to a state of strong non-equilibrium.
In superconductor-semiconductor systems the electrons in the low-dimensional electron system of
the semiconductor are Andreev-reflected at the interfaces to the superconductor.
Current distribution just below the surface of a 20 nm thick permalloy slab with gold voltage probes on top.
Colors indicate the absolute value of the current (red - high, blue - low).
The bright lines indicate five current paths.
In this subject area we particularly aim at a better understanding of the influence of
spin-polarized currents on the magnetization dynamics.
The theoretical description is based on the nonlinear Landau-Lifshitz-Gilbert equation
for the magnetization and quantum mechanical equations of motion for
local spinor density matrices. The coupled nonlinear partial differential equations
can be solved analytically only in case of high symmetry.
Otherwise we will solve them by numerical methods.
S. A. Solin,
"Magnetic Field Nanosensors",
Scientific American 291, 45 (2004).
"Electronic Transport in Mesoscopic Systems",
Cambridge Studies in Semiconductor Physics and Microelectronic Engineering, Cambridge University Press, 1995.
B. Krüger, D. Pfannkuche, M. Bolte, G. Meier, and U. Merkt,
"Current-driven domain-wall dynamics in curved ferromagnetic nanowires",
Phys. Rev. B 75, 054421-1-054421-9 (2007).
Theory of current and spin transport through narrow domain walls