prof. dr hab. inż. Arkadiusz Wójs , PWr

Fractional skyrmions in quantum Hall systems

The talk will review the physics of skyrmions formed in ferromagnetic quantum Hall states of 2D electrons in a high magnetic field. They carry electric charge, angular momentum, and massive spin. Their emergence as low energy charged quasiparticles in a ferromagnetic ground state causes depolarization and supports spin-flip excitations with energies below the single-electron spin splitting which can be probed by Raman spectroscopy. Skyrmions have also been predicted in ferromagnetic fractional quantum Hall (FQH) systems, such as Laughlin incompressible liquid at the Landau level filling factor ν=1/3. Understanding of the FQH effect involves exotic emergent topological particles, such as fractionally charged quasiparticles, composite fermions (CFs), nonabelian anyons, or Majorana fermions. In particular, incompressibility and the excitation spectrum of the many known FQH ground states is underlied by the formation of essentially free CFs from strongly correlated electrons – through binding of pairs of vortices of the many-electron wave-function as a result of Coulomb interaction in a degenerate Landau level. As fractional quantum Hall states of electrons correspond to integral quantum Hall states of CFs, fractional skyrmions emerge as topological spin textures in the CF ferromagnets. Owing to different form and reduced energy of effective CF interaction, the hypothetical fractional skyrmions are fragile objects, easily suppressed by even fairly weak Zeeman effect.