TEMSSOC · TOPOLOGICAL EFFECTS IN MATTER WITH STRONG SPIN-ORBIT COUPLING

This theoretical project addresses novel quantum phases of matter whose low energy properties are dominated by topological excitations: Majorana fermions in topological insulators, skyrmions in chiral magnets and magnetic monopoles in pyrochlore magnets. It is motivated by the recent experimental discovery of topological insulators (HgTe/CdTe,Bi1-xSbx or Bi2Se3), the mounting evidence for skyrmions in the chiral magnet MnSi (anomalous Hall effect measurements in 2009) and the prediction of magnetic monopoles in spin ice (by Roderich Moessner and co-workers in 2008). During the outgoing phase in UC Berkeley, we shall consider the interplay of interaction and spin-orbit effects in topological insulators both in bulk materials and in their heterostructures. The fellow researcher has previously studied heterostructures combining superconductors and ferromagnets. Majorana fermions are expected to appear when such heterostructures are deposited on top of a three-dimensional topological insulator. Moreover A. Vishwanath (outgoing host researcher) initiated the research on spin crystals and skyrmions in chiral magnets. During the return phase in MPIPKS Dresden, we shall investigate the properties of the magnetic monopoles predicted by Roderich Moessner (scientific in charge of this project) in spin ice (Dy2Ti2O7,Ho2Ti2O7). The mechanisms of the anomalous Hall effect in itinerant pyrochlore ferromagnets (Nd2Mo2O7, Pr2Ir2O7) will also be considered. Finally the present project will foster the study of topological insulators in the EU community, while these compounds have been almost exclusively studied in the USA so far. The present project is also relevant for other branches of physics since, in spite of a longstanding and on-going hunt, Majorana fermions, skyrmions and monopoles are still to be found in high-energy and nuclear physics.