31.1.2020 New forms of superconductivity (Aikebaier)

Superconductivity, a quantum mechanical phenomenon exhibits vanishing electrical resistance of some materials, takes place at sufficiently low temperature. For metals, for example, the transition temperature is below minus two hundred celsius degrees. Moreover, superconductivity do not like magnetic fields or ferromagnetism, which is another quantum mechanical phenomenon exhibiting strong magnetisation in some other types of materials. Aiming to increase the critical temperature of superconductivity and combine the superconductors with magnetic materials, in his dissertation Faluke Aikebaier studied superconductivity in Dirac materials, and various properties of superconductors making contact to ferromagnetic insulators. These can be understood as new forms of superconductivity.
Published
31.1.2020

The results show that superconductivity in Dirac materials (in certain conditions) suggests a new way to reach the high critical temperature superconductivity, and the various properties of superconductors making contact to ferromagnetic insulators enrich our understanding of the magnetic properties of superconductors.

Dirac materials are a class of materials, of which properties, at least in some regimes, can be described by the Dirac equation (for example, the famous one atom layer thick material, graphene). It was suggested that if the lattice structure of such materials is deformed (known as strain), then the effective mass of the electrons are enhanced on a considerable extent. This results the flat (energy) band.

The research shows an enhanced superconductivity in strained Dirac materials, and an estimated critical temperature for graphene reaches the room temperature (25 Celsius degrees).

Superconductivity near a ferromagnetic insulator

Superconductors and ferromagnets do not coexist. In the jargon of physicist, these two are called antagonist orders. However, in certain conditions, the combination could be achieved in hybrid structures. In the case of a superconductor with a ferromagnetic insulator, since the ferromagnet is an insulator, the properties of superconductor is affected by the magnetic order, and reveals new features which do not exist in either types of materials alone.

The research in the dissertation concerning this direction studies various transport phenomena in such hybrid structures. The dissertation, on the one hand, filled many gaps in the previous research by studying new features and making new predictions in such hybrid structures, on the other hand, contributes to the timely new topics to the field. For example, contributions to superconductor based detector technology.

Overall, the research reveals interesting properties of superconductors, particularly on the effort of searching high temperature superconductivity and investigating various properties of superconductors based hybrid structures.

The research is published in JYU Dissertations -series, number 188, 2019, Ä¢¹½Ö±²¥. ISBN 978-951-39-8036-8 (PDF) URN:ISBN:978-951-39-8036-8 ISSN 2489-9003.
Link to publication:

M.Sc. Faluke Aikebaier defends his doctoral dissertation in Physics "New forms of superconductivity" on Friday 31st of January 2020 at the Department of Physics (Ylistönrinne, Survontie 5) at 12:00. Opponent is Dr. Manuel Houzet (Institute of Nanosciences and Cryogenics, CEA and Université Grenoble Alpes, France) and Custos is Professor Tero Heikkilä (Ä¢¹½Ö±²¥). The doctoral dissertatiion is held in English.

For further information:
Faluke Aikebaier, faluke.aikebaier@jyu.fi 
Communication officer Tanja Heikkinen, tanja.s.heikkinen@jyu.fi, tel- +358 50 581 8351