Research Summary:

The new high-temperature cuprate superconductors offer a rich field for Professor Markiewicz's research. Presently, Professor Markiewicz is modelling 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 can provide 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. Quite recently he has developed a general technique for exploring competing magnetic and charge-ordered phases in these materials, and has found a promissing candidate for the phase seen in STM studies.

These results provide an extension of 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. 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 graphites as a function of magnetic field.

Recent Publications:

J. Nieminen, H. Lin, R.S. Markiewicz, and A. Bansil, "Origin of the Electron-Hole Asymmetry in the Scanning Tunneling Spectrum of the High-Temperature Bi₂Sr₂CaCu₂O_8+δ Superconductor", Phy Rev. Lett. 102, 037001 (2009).

R.S. Markiewicz, and A. Bansil, "Magnetic mechanism of quasiparticle pairing in hole-doped cuprate superconductors", Phys. Rev. B 78, 134513 (2008).

R.S. Markiewicz, S. Sahrakorpi, and A. Bansil, "Paramagnon-induced dispersion anomalies in the cuprates", Phys. Rev. B76, 174514 (2007).

Tanmoy Das, R.S. Markiewicz, and A. Bansil, "Nodeless d-wave superconducting pairing due to residual antiferromagnetism in underdoped Pr_2-xCe_xCuO_4-δ ", Phys. Rev. Lett. 98, 197004 (2007).

R.S. Markiewicz and A. Bansil, "Collapse of the Magnetic Gap of Cuprate Superconductors within a Three-Band Model of Resonant Inelastic X-Ray Scattering", Phys. Rev. Lett. 96, 107005. (2006).