Research and Scientific Interests

From ArneBrataas

Mesoscopic Physics

Quite recently, a new field, mesoscopic physics, has emerged. The word mesoscopic originates from mesos, meaning something in between. Small systems whose dimensions are intermediate between the microscopic and the macroscopic are called mesoscopic. Developments in nano-technology make it possible to realize electronics circuits that are as small as 10 nm. In order to incorporate these systems into modern technologies, it is necessary to understand the physical properties via fundamental research. Researchers are therefore trying to understand the physical properties of systems that are not as small as a single atom, but small enough that the physical properties can be dramatically different from those in a larger chunk of material. Mesoscopic systems display a variety of physical effects that have needed new or improved theoretical methods to describe them. For systems smaller than the inelastic scattering length, quantum size effects in small particles and quantum interference between strongly coupled particles give rise to new phenomena. The discrete electrostatic energy of a small system by the addition of a single electron governs the transport properties at low voltages, a phenomenon known as the Coulomb blockade effect. Quantum confinement creating low-dimensional systems leads to novel physics like the quantum Hall effect and fractional quantum Hall effect. From a theorist’s point of view, mesoscopic systems are “laboratories” for how electrons propagate in a solid. The parameters of the system are rather well controlled and allow fundamental studies on a series of experimentally controllable feasibility models. We therefore plan to study the fundamental physics of novel mesoscopic systems comprising ferromagnets, semiconductors, superconductors and combinations thereof.

Spintronics and Magnetoelectronics

Metallic ferromagnets in contact with conductors inject a spin-polarized current in, e.g. simple normal metals, semiconductors or superconductors. On the other hand, transport in mesoscopic devices test basic concepts of quantum mechanics, such as charge and conductance quantization. The behaviour of a collection of spins in such structures combines these two fields. Our aim is to develop novel or improved theoretical methods for understanding transport and other phenomena in such systems.

Recently, it has been realized that the spin of the electron provides new functionality in electronics applications. The giant magneto resistance (GMR) in magnetic metallic multilayers discovered only ten years ago has very recently been applied to magneto-resistive read heads for hard disks in high-end desktop computers. Albert Fert and Peter Grunberg were awarded the 2007 Nobel Prize of physics for their discovery of the giant magnetoresistance effect, see http://nobelprize.org/nobel_prizes/physics/laureates/2007/index.html. The GMR is a result of the spin-dependent scattering by defects and interfaces. Devices that use the spin of the electron rather than only its charge have been coined “spintronic” circuits in the spirit of conventional electronics. Spintronic devices could also be used as nonvolatile magnetic random access memory.

Research Topics

Our research is within mesoscopic physics with emphasis on spintronics and magnetoelectronics. Some of the topics we study are

• AC Magnetoelectronics
  • Spin-torques
  • Spin-pumping
  • Magnetization dissipation and fluctuations
• DC Transport in Ferromagnets
  • Anomalous Hall effect
  • Ferromagnetic semiconductors
  • Domain Wall resistance
• Graphene
  • Spin transport and spin relaxation
• Mesoscopic superconducting-ferromagnetic systems
  • Full Counting Statistics
  • Crossed Andreev reflection
  • Spin injection and spin relaxation