Probing spin polarization of quantum Hall states by tunneling into a quantum Hall ferromagnet.*

Interactions between electrons lead to a plethora of spin configurations of a two-dimensional electron system subjected to a perpendicular magnetic field. We have developed a pulsed tunneling method that can probe the spin texture of both the ground and the excited states of quantum Hall systems. Employing a bilayer magnetic tunnel junction consisting of one fully spin-polarized layer and another layer with tunable filling factor, we measured the filling factor dependence of spin-polarized currents flowing between the two layers. Our data show an oscillating pattern of the spin-polarized currents. In particular, the drastic decrease of the spin-polarized current near ν = 1 is consistent with the formation of skyrmions. At high energy we observe spin-selective tunneling arising from two-body Haldane pseudopotentials, which have been key ingredients for describing the strong electronic correlations in quantum Hall systems. This work demonstrates that our pulsed tunneling method offers a new experimental tool for studying the many-body states, possibly including the exotic fractional quantum Hall state at ν = 5/2.