Christian Pfleiderer

Title

Condensed Matter Particle Physics

Abstract

Particle physics raises many fascinating questions. However, tremendous efforts are necessary to explore these questions experimentally and most issues may never be settled. Condensed matter systems exhibit intimate analogies with particle physics suitable for experimental exploration. Examples include the Higgs mechanism in superconductors, magnetic monopoles in frustrated magnets and Majorana fermions in topological insulators. I will present recent experimental studies in chiral magnets that allude to a research program initiated by Heisenberg, notably how to go beyond particle-wave duality. Using neutron scattering we identified a new form of magnetic order in certain chiral magnets, which is composed of topologically stable knots in the spin structure, so-called skyrmions. The skyrmions may be viewed as particle-like states of continuous fields, forming lattice structures as well as amorphous and glassy phases reminiscent of vortex lines in superconductors. In the electronic transport properties the skyrmions give rise to a quantized Berry phase causing a new form of Hall effect, the topological Hall effect. Most remarkably, perhaps, we observe large spin transfer torque effects mediated by this Berry phase at ultralow current densities. This illustrates how issues in fundamental physics connect with challenges in applied physics.