Abstract: We introduce two-dimensional fermionic band models with two orbitals perlattice site, or one spinful orbital, and which have a nonzero topological Chern number that can be changed by varying the ratio of hopping parameters. When a Hubbard interaction is introduced, the effective hopping parameters are renormalized and the system’s topological number can change at a certain interaction strength, U = \bar U, smaller than that for the Mott transition. Two situations may occur: Either the anomalous Hall conductivity changes abruptly at \bar U, or the transition is through an anomalous Hall metal, or \sigma_xy changes smoothly between two different quantized values as U grows. Restoring time-reversal symmetry by adding spinto spinless models, the half-filled system becomes a Z2 topological insulator. The topological number \nu then changes at a critical coupling \bar U and the quantized spin Hall response changes abruptly. We also study a triplet superconductor with p-wave symmetry in the presence of Rashba spin-orbit coupling and externally applied Zeeman spin splitting. Topological superconductors may undergo transitions between phases with different topological numbers which are related to the presence of gapless (Majorana) edge states. In a superconductor, however, charge is not conserved. Therefore, \sigma_xy is not quantized. It is shown that while \sigma_xy evolves continuously between different topological phases of a Z topological superconductor, its derivatives display sharp features signaling the topological transitions.

 

About the Speaker: Miguel Araujo obtained his PhD in Physics in 1995 from Cambridge University, UK. Since 1996, he is Assistant Professor at University of Évora, Portugal.  He is member of the Research Center CFIF at IST-Lisbon, since 2006, and Associate Member of CSRC, Beijing, since 2012. His main research topics in the Theory of Condensed Matter include electron correlations, superconductivity in heavy fermion compounds and ironpnictides, topological insulators and superconductors.

  

Date&Time: July 17, 2013 (Tuesday), 10:00 - 11:00 a.m. 
Location: 606 Conference Room