Single Review on past events

In his presentation on “Spin-electronics with single atoms” Torsten Pietsch demonstrated how future electronic devices could look like and how atomic contacts may be used to develop new device concepts. But first he explained the problem with presently used silicon-based technologies in microelectronics that someday will reach a limit: “Compared to the development of the automotive industry over the past 100 years – where we still have more or less the same: 4 wheels, a seat, and an engine of some sort – the evolution of electronic devices in a broader sense over the same period of time is simply staggering. In 1900 there were simple, mechanical calculation machines, barely able to handle the four basic arithmetic operations. Today‘s devices have almost nothing in common with its early predecessors. They perform billions of operations a second, consume almost no energy at all and are affordable for almost everybody.” Gordon Moore used to say, if the automotive industry evolved at the same rate as microelectronics “a Rolls-Royce would get a million miles per gallon of fuel, travel at several hundred thousand miles per hour and it would be cheaper to throw it away than to park it...”

Microelectronic devices consist of printed circuit boards with components and chips that are made of very small silicon structures (wires, capacitors and transistors) invisible to the naked eye. “The development of transistor technologies is of paramount importance for the miniaturization of silicon electronics”, Torsten Pietsch stated. “But after 50 years of exponential evolution silicon microelectronics can no longer just scale to below few nanometers”. Leakage of currents, energy dissipation, thermal instabilities, finite size effects or the quantum nature of matter as well as economic issues may impede the further scaling of transistors and other devices.

For this reason new methods have to be explored, for example with single atoms. But what‘s so interesting about atomic-size wires or junctions? “Atomic contacts are very simple and a well-defined system that allows for studying fundamental properties of matter. Sometimes new phenomena emerge that are interesting for future applications and have great potential for devices with ultimate “smallness”.

Currently spin-based technologies are being developed. Spin is a quantum mechanical property of the electron, and spin-based electronics means a new technology that, in a way, teaches electrons new tricks. The development of these new technologies is heavily based on the synthesis of suitable material, more precisely on „magnetic” material. Magnetism is a collective property of spins, therefore spin-electronics relies on “magnetic” materials. “In such magnetic materials, we call them ferromagnets, there are more electrons of one type then of the other, this makes them magnetic and polarizes the electrical current.” Based on the interaction of spin with other quasiparticles in solid state structures novel types of circuits can be devised. The study of these effects is the foundation of an emerging research field, which he calls Spin-Xonics: “X stands for any interaction of spin with some other quasiparticle or degree of freedom, for example interactions of spin with photons would be called spin-photonics, the interaction of spin with heat spin-caloritronics….”

In his research project Torsten Pietsch works on non-equilibrium effects and the coupling of spins and optical degrees of freedom in magnetic point contacts. Injecting spin-polarized electrons in magnetic hetero point contacts to create a new THz light source is one example of a new physical phenomenon he studies via electronic transport measurements and which are extremely interesting for future applications.