****NON-TECHNICAL ABSTRACT**** Two major themes in condensed matter physics are quantum critical phenomena and unconventional superconductivity. A quantum phase transition takes place when quantum matter becomes unstable to a new, ordered ground state. Therefore, quantum criticality is a concept that describes a phase transition between competing ground states driven by an external parameter other than temperature such as chemical composition, pressure, or magnetic field. In principle the phase transition takes place at absolute zero. Nevertheless, a growing body of experimental work indicates that fundamentally new physics can develop over a wide region at finite temperatures. The goal of this research project is to enhance our fundamental understanding of the extent to which quantum criticality controls the finite temperature properties of unconventional superconductors and provide insight into the mutual interplay between unconventional superconductivity and magnetism. The results from these basic investigations are expected to provide further understanding of the interplay between magnetism and superconductivity and to facilitate applications to electronic sensors and devices such as magnetic field sensors or even computer logic devices. This highly interdisciplinary project will allow graduate students and postdocs to benefit from exposure to a diversity of important experimental techniques and a variety of different physical systems and phenomena. The diversity of the expertise gained by the participants in this research program is a substantial advantage in today's knowledge based, technology driven economy, being beneficial to a future career in industry, government, or academia.
This individual investigator award supports a research project addressing major themes in condensed matter physics: quantum criticality and unconventional superconductivity in Fe pnictides, and the interplay between superconductivity and magnetism in pnictides and hybrid ferromagnet/superconductor (F-S) structures. These studies are expected to significantly enhance our fundamental understanding of the extent to which quantum criticality controls the finite temperature properties of unconventional superconductors and promise a deeper insight into the mutual interplay between unconventional superconductivity and magnetism. In addition by comparing and contrasting the Fe-pnictides and cuprates superconductors, the project may contribute to uncovering the vital clues that theorists need to solve the mystery of high-temperature superconductivity. The strong mutual interaction between the ferromagnetic and superconducting subsystems of heterogeneous F-S structures does not suppress either property, but rather can dramatically change the structure and properties of both of them. Therefore these structures offer unlimited possibilities for qualitatively new science and technologies. For example, such structures offer important technological promise for devices whose transport properties can be easily tuned by comparatively weak magnetic fields. This highly interdisciplinary project will allow graduate students and postdocs to benefit from exposure to a diversity of important experimental techniques and a variety of different physical systems and phenomena. The diversity of the expertise gained by the participants in this research program is a substantial advantage in today's knowledge based, technology driven economy, being beneficial to a future career in industry, government, or academia.
