Research in quantum impurity creating new ways to store data

Ljubljana, 19 November - Rok Žitko is a researcher at the Theoretical Physics Department of the Jožef Stefan Institute (IJS), where the focus of his research in the the last four years has been quantum impurity. Breakthroughs in the field could lead to a new way to store data.

Žitko, who also teaches at the Ljubljana Faculty of Mathematics and Physics, is currently researching with his colleagues at the IJS the phenomena caused by magnetic impurities in metals. It is possible today to directly measure the properties of individual magnetic atoms on the surface of a matter by using scanning tunneling microscopes, which provide a much better insight than measuring of the average properties of impurities distributed on the entire sample, Žitko explained.

"All of this becomes especially interesting if the metal is super-conductive. Here every magnetic impurity partially 'corrupts' the superconductivity in its vicinity, which results in additional excited energy states, which correspond to the tying of electrons from the superconductor to impurities. When supplied with energy, impurities can be brought from the basic state to the excited state. At sufficiently low temperatures the excited quantum state is very long-standing, making it possible to store data in this way," Žitko explained.

According to him, miniaturization of media for magnetic storage of data leads to one bit of information being recorded on an increasingly smaller magnetic area. Progress in this field will lead to the physical limit or super-paramagnetic limit. In this way magnetic islands with the size of only a few thousand or even a few hundred atoms will be used in bit-patterned media with nanotechnological procedures, Žitko explained.

"In order to make data storage reliable, we need a better grasp of the magnetic properties of such small magnetic areas, whose properties do not differ from extensive magnetic materials or from small clusters of magnetic impurities, and for which adequate theoretical description methods still need to be developed."

Some of Žitko's theories about the influence of magnetic anisotropy on excited states were recently experimentally confirmed by the tunneling microscopy group at the Free University of Berlin. The confirmation of theories brings special satisfaction to theoretical physicists, according to Žitko.

According to him, experimental and theoretical physics are strongly intertwined, while the difference between them lies primarily in methodology. "Perhaps it was true decades ago that the person who conducts an experiment is capable of developing a theory on their own. Today, these theoretical tools are so advanced that individuals can truly master only their own niche."

Žitko explained that theoretical physicists are interested in phenomena per se and not so much in their application. "I look at physics as a field that satisfies our curiosity, which frequently has some applicable value, but this is not the focus of our work," he added.

According to him, there is a shortage of theoretical physicists despite the fact that they are very active. "The problems we are dealing with have become so complex that an individual cannot do much alone, since you need some critical mass of very capable people in order to tackle the problem."

About the Theoretical Physics Department
The Theoretical Physics Department at the Jožef Stefan Institute, which has been active since the beginning of the 1960s, is currently headed by Svjetlana Fajfer. It features three groups of researchers dealing with theoretical solid-state and statistical physics, the theory of nuclei, elementary particles and fields, and with biophysics and soft condensed matter. A total of 37 researchers currently work at the department, of which 10 are junior researchers. Last year five employees defended their doctoral dissertations, according to Fajfer.

The Theoretical Physics Department generates a large number of EU projects, and has in the last five years participated in research as part of six EU projects. The members of the department published a total of 105 papers in 2014, including in some of the most renowned international journals, such as Nature in Science. In the last ten years three department members have received the Zois Prize, the highest national award for scientists and scholars.

Research activity of the department is focused on current theoretical problems in solid state physics, statistical physics, nuclear physics, elementary particle physics and field theory, and in biophysics and physics of soft condensed matter. It has established close cooperation with the experimental groups at the Jožef Stefan Institute, and with institutes and universities in Slovenia and abroad. Department members participate in numerous international research projects, according to the IJS website.

Researcher Rok Žitko
Rok Žitko is a researcher at the Theoretical Physics Department at the Jožef Stefan Institute (IJS), where he has worked since 2002. In 2008 he received the Jožef Stefan gold medal, the highest accolade for young doctors of science, for his successful doctoral dissertation "Multi-particle effects in resonant tunneling of electrons through nanostructures".