Skyrmion is the Limit: Twisted Topological Excitations and Emergent Phenomena
Avadh Saxena (Theoretical Division, Los Alamos National Lab)
Stable topological excitations such as domain walls and vortices are ubiquitousin condensed matter as well as high energy physics and are responsible for manyemergent phenomena including electromagnetism. Recently a new mesoscopic spin texture called skyrmion was discovered experimentally in certain conducting and insulating magnets. It is now believed to exist in Bose-Einstein condensates, superconductors, 2D electron gases, nematic liquid crystals among other physical systems. This topological excitation was originally proposed by Tony Skyrme in 1958 in a nonlinear field theory of baryons. In the temperature-magnetic field phase diagram of chiral magnets, skyrmions form a triangular lattice in the low temperature and intermediate magnetic field region and are stabilized by the spin-orbit interaction. In metallic magnets, skyrmions can be driven by a spin polarized current. I will first briefly discuss the experiments and then model the skyrmions in a nonlinear sigma model with anisotropy and the spin-orbit term. Then I will discuss our recent work which explains the weak pinning of skyrmions due to the Magnus force. Next, I will show how one can get merons (half-skyrmions) and magnetic monopoles in this model. Finally I will compare skyrmions with other topological objects such as vortices in type II superconductors and discuss some exotic phenomena, e.g. the spin Seebeck effect.
Brief bio: Avadh Saxena is Group Leader of the Condensed Matter and Complex Systems group (T-4) at Los Alamos National Lab, New Mexico, USA, where he has been since 1990. He is also an affiliate of the Center for Nonlinear Studies at Los Alamos. His main research interests include phase transitions, nonlinear phenomena, geometry, topology, optical, electronic and vibrational properties of functional materials, device physics and soft condensed matter. He holds adjunct professor positions at the University of Barcelona, Spain and the University of Arizona, Tucson. He is Scientific Advisor to National Institute for Materials Science (NIMS), Tsukuba, Japan. He is a member of American Physical Society, Materials Research Society and the Sigma Xi Scientific Research Society. His early work on skyrmions was in the Discovery News and NBC News (Aug. 2013). Contact him at: avadh@lanl.gov