Probing a quantum Hall pseudospin ferromagnet by resistively detected nuclear magnetic resonance

摘要

Resistively detected nuclear magnetic resonance (RD-NMR) has been used to investigate a two-subband electron system in a regime where quantum Hall pseudospin ferromagnet (QHPF) states are prominently developed. It reveals that the easy-axis QHPF state around the total rilling factor v=4 can be detected by the RD-NMR measurement. Approaching one of the Landau-level (LL) crossing points, the RD-NMR signal strength and the nuclear-spin-relaxation rate 1/T_1 enhance significantly, a signature of low-energy spin excitations. Furthermore, the RD-NMR signal at another identical LL crossing point is surprisingly missing which presents a puzzle. These observations demonstrate that the spin freedom may play an role in the understanding of the QHPF states.