Unconventional Superconductivity

High temperature superconductivity was discovered in 1986, and, despite almost thirty years of intense research, the underlying physics of these materials is still not understood. However, the observation of unconventional superconductivity in many materials including the whole class of copper-oxide compounds, the iron pnictides an chalcogenides, heavy Fermion materials, and charge-transfer salts, has given us hope that this phenomenon may be the result of some general features of Mott physics or quantum critical physics, instead of being a delicate, material-specific phenomenon.

Much of our work focuses on the iron based compounds, which have the second highest transition temperatures, after the cuprates. As in the cuprates, the normal state above the superconducting transition show a number of properties that do not fit into the standard theory of metals, possibly due to the presence of a quantum critical point (zero-temperature phase transition) under the superconducting dome. For example, the electrical resistivity in these materials does not show the standard T2, B2 dependencies. [] We do careful transport studies to identify where this anomalous behavior arises and to search for possible scaling behavior associated with a quantum critical point.

Even after twenty-eight years, progress continues in our understanding of the cuprate superconductors, with recent work pointing to the existence of a Fermi-liquid ground state. [] We have taken a particular interested in some nominally undoped Pr2CuO4 thin films that show superconductivity. [] We hope to elucidate the relationship between the electronic state in these thin films and that in the traditional, doped single crystal samples with high field magnetotransport studies.

The_EgyptianP-substituted BeFe2As2

We study the physics of high-Tc superconductors like P-substituted BaFe2As2 in extremely high magnetic fields, where the magnetic field itself begins to compete with other relevant energy scales.

E213179e_04 (Device 1 on puck - after)_tw1Cuprate superconductivity

Despite 30 years of research, the problem of cuprate superconductivity remains unsolved. By taking advantage of recent developments on thin-film high-Tc materials growth, we hope to measure and tune the quasiparticle dynamics of these systems.

PCO_film1Quasi-one dimensional superconductivity

In some exotic systems there is a superconducting instability in the presence of large anisotropies in the quasiparticle dynamics. One of our interests is the interplay between dimensionality and superconductivity.