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Elementary Particle & Astroparticle Physics
Nanophysics & Condensed Matter Physics
Biological Physics
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Experimental Nanophysics Robert Markiewicz Professor PhD University of California at Berkeley, 1975 (617)373-2916 markiewic@neu.edu Research Summary: The new high-temperature cuprate superconductors offer a rich field for Professor Markiewicz's mixture of experimental and theoretical research. His experimental studies, carried on in close collaboration with B. C. Giessen (Department of Chemistry and Barnett Institute), have included synthesis of new materials (including the first four copper layer superconductor, TlBa2Ca3Cu4Ox, Tc=122K) and studies of flux-lattice melting in strong magnetic fields. Presently, Professor Markiewicz is working on the critical current problem in these materials. The critical currents in bulk samples of the cuprates are found to be extremely low. This is due in part to simple misalignment of crystal axes across a grain boundary, which leads to a weak link connecton across the ensuing dislocation array. He and Professor Giessen have patented a technique of aligning two orthogonal axes of the individual grains in a powder prior to sintering and they are now exploring how biaxial alignment can be combined with partial-melt-regrowth procedures for improving critical currents. In theory, Professor Markiewicz is currently exploring the possibility that high-temperature superconductivity is 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, which has recently been confirmed by photoemission measurements. An interesting outcome of this research is to show that there is an extremely large electron-phonon coupling associated with the saddle points, and hence there should be a competition between superconductivity and structural disorder. The strong electron-phonon coupling can easily be understood in terms of the Jahn-Teller effect, with the electronic degeneracy due to the presence of two van Hove singularities. In the La2-xAxCuO4 (A=Ba, Sr) superconductors, low-temperature tetragonal and orthorhombic phases may be related to static or dynamic Jahn-Teller phases. This structural instability may be the origin of the pseudogap found when these materials are underdoped. This research is a natural extension of Professor Markiewicz's earlier research on 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: R.S. Markiewicz, and A. Bansil, "Dispersion anomalies induced by the low-energy plasmon in the cuprates", Phys. Rev. B 75, 020508 (2007). Tanmoy Das, R.S. Markiewicz, and A. Bansil, "Nodeless d-wave superconducting pairing due to residual antiferromagnetism in underdoped Pr2-xCexCuO4-δ" Phys. Rev. Lett. 98, 197004 (2007). H. Lin, S. Sahrakorpi, R.S. Markiewicz, and A. Bansil, "Raising Bi-O Bands above the Fermi Energy Level of Hole-Doped Bi2Sr2CaCu2O8+δ and Other Cuprate Superconductors", Phys. Rev. Lett. 96, 097001 (2006). 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). S. Sahrakorpi, M. Lindroos, A. Bansil, and R.S. Markiewicz, "Evolution of Mid-gap States and Residual Three Dimensionality in La2-xSrxCuO4"", Phys. Rev. Lett. 95, 157601 (2005). |