Research: Quantum Criticality and Unconventional Superconductivity
The need to understand the collective instabilities resulting from electronic interactions and to harness the resulting emergent behaviors such as superconductivity and magnetism are the central motivations for this research project. We know that the most extreme electronic correlations are found near quantum critical points, where the suppression of competing phases and incipient electronic localization that are driven by strong interactions lead to new collective phases, such as unconventional superconductivity. We are investigating the extent to which this scenario, developed for strongly correlated materials like cuprates, heavy fermions, and iron pnictides, is appropriate for more conventional materials with weaker correlations. Developing a holistic phase diagram that is suitable for materials with different correlation strengths where superconductivity and magnetism are separate regimes, will provide direction for the discovery of new materials with purpose-built functionality, which are the feedstock for advancing new technologies for sensor and device applications, as well as energy conversion and distribution applications.At present, we are seeking new families of unconventional superconductors near quantum critical points in iron-based compounds. Our laboratory combines a vigorous program of materials synthesis with magnetization, specific heat, and electrical transport measurements to identify new compounds that order magnetically at low or vanishing temperatures. Via collaboration with groups at Brookhaven Naitonal Laboratory, photoemission and optical spectroscopy measurements will be used to study the evolution of the electronic structure and correlations as the system is compositionally driven through magnetic instability at the quantum critical point. Neutron scattering and x-ray magnetic circular dichroism measurements will quantify moment localization in the ordered, quantum critical, and normal metal phases.