Emergent Phenomena of Complex Electronic Materials
C. Pfleiderer
Physik-Department, Technische Universität München, Germany E-Mail: christian.pfleiderer@frm2.tum.de
Complex electronic materials display emergent phenomena in intimate analogy with a wide range of different areas in physics. 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 torques mediated by this Berry phase at ultra-low current densities. This illustrates how emergent phenomena of complex electronic materials connect issues across a wide range of areas in physics with challenges in applied physics.
