Resolving competing orders and symmetry-breaking in cuprate and iron pnictide high temperature superconductors using infrared Hall measurements

Non-Technical Abstract Superconductors conduct electricity without any resistance and have provided fascinating new science as well as important new technologies (from medical imaging to high energy particle accelerators to telecommunications filters to maglev trains). One of the biggest technological challenges of conventional superconductors is that they have to be cooled to very low temperatures using expensive and increasingly scarce liquid helium. This award supports research on new materials that superconduct at significantly higher temperatures and have challenged our understanding of superconductivity. These high temperature superconductors have attracted a great deal of attention in the last three decades for their rich and often unresolved behavior as well as their technological applications. The researchers at the State University of New York at Buffalo use new infrared techniques they developed to explore how these materials behave as a function of chemical composition, magnetic field, temperature, and probing frequency. The project involves graduate and undergraduate students. The outreach program involves a public high school in Buffalo and will have a large impact on urban mixed-income public school students. Technical Abstract This award from the Condensed Matter Physics program in the Division of Materials Research supports research on cuprate and iron pnictide high temperature superconductors (HTS) at the State University of New York at Buffalo. HTS materials have attracted a great deal of attention in the last three decades for their rich and often unresolved behavior as well as their technological applications. Due to the characteristic energy scale of many of these properties and the unique ability of magneto-polarimetry to probe asymmetries and order in the electronic structure, these HTS are extremely well-suited for exploration using terahertz Hz (2-6 meV) and infrared (IR: 100-1200 meV) Hall measurements. The principal investigator studies a wide range of HTS materials as a function of doping, temperature, probe energy, and magnetic field. The sensitivity and broad spectral extent of the proposed measurements provide new insights into the unusual pseudogap phase (PGP) in these HTS materials, as well as new information about charge, spin, and magnetic ordering. A key question in the cuprates is whether the PGP is simply a precursor to superconductivity or whether it is a fully fledged new phase with its own broken symmetry. The objective is to provide insight into the mechanism(s) breaking the symmetry. In the iron pnictides, the work explores a wide range of anomalous behavior, including anomalous optical absorption far above the superconducting gap, unusual spectral weight transfer in the IR, possible coexistence of magnetism and superconductivity, spin-ordering, and a PGP. The research involves undergraduate students and two PhD students.