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Exploring Orbital Freedom – Steven Johnston


The real world applications of superconductors are practically limitless. For example, recent advances in transportation like magnetically levitating trains, and advances in medical diagnostics are largely based on our knowledge of superconductors.

The recent discovery of superconductivity at high transition temperatures in a class of iron-based materials has prompted a renewed interest in the role of electron mobility and orbital degrees of freedom in superconductivity. Traditionally, high-temperature superconductivity is found when additional electrons are added to an insulating material. However, the new iron based superconductors seem to display a dual nature, where the electrons behave as if they have both localized (insulating) and mobile (conducting) characteristics. Understanding the nature of this duality may hold the key for understanding superconductivity.

Johnston solo web edit“Iron pnictide superconductors have this really weird dichotomy in a sense,” said Dr. Steven Johnston. “They move around easily but they can be mobile and immobile. They have sort of a pneumatic dynamic nature.”

Johnston’s JDRD project seeks to explore the underlying physics of these superconductors, with the guiding notion that the selective mobility of electrons is tied to the multi-orbital nature of the pnictides. His team will utilize extensive one-dimensional models in order to study large system sizes and investigate how the mobility of electrons is affected by factors such as the number of orbitals or the presence of defects in the material. Previous techniques used to study this problem in three-dimensional models have largely been restricted to only a handful of atomic sites, where they are unable to address these questions.

The project is currently on track, generating preliminary results needed to move forward and positioning Johnston’s JDRD team, and UT, to make new and leading contributions to research on materials with orbital degrees of freedom, including but not limited to iron pnictide superconductors.

JDRD funded research 1/1/2015-12/31/2015