The new high-temperature cuprate superconductors offer a rich field for Professor Markiewicz’s research. Presently, Professor Markiewicz is mode ling the spectral responses of a variety of experimental probes, including angle-resolved photoemission spectroscopy (ARPES), optical spectra, resonant inelastic X-ray scattering (RIXS), and scanning tunneling spectroscopy (STM) — the very probes that are providing continual new insights into the physics of the cuprates. He has developed an intermediate-coupling model of the cuprates, which provides a detailed explanation of all these spectroscopies over a wide doping and energy range. He has shown that the relevant magnetic fluctuations are strong enough to provide the pairing in these materials, and lead to the dominant competing phase for electron-doped cuprates. He has developed a general technique for exploring competing magnetic and charge-ordered phases in these materials, and has found a promising candidate for the phases seen in STM studies.
These results extend his earlier work studying nanoscale phase separation and other instabilities associated with peaks in the density of states, due to the proximity of a saddle point van Hove singularity to the Fermi level in these cuprates. In addition to cuprates, Professor Markiewicz is studying a variety of correlated metals and topological insulators. Professor Markiewicz’s pre-cuprate research involved anomalous electronic states in predominantly two-dimensional systems. This work included studies of electron-hole droplets in germanium; localization, interaction, and quenching of superconductivity in ultrathin metal films; and the crossover to two-dimensional electron gases in intercalated graphite as a function of magnetic field.