Breakdown of Particle-Hole Symmetry in the Lowest Landau Level Revealed by Tunneling Spectroscopy

Tunneling measurements on 2D electron gases at high magnetic field reveal a qualitative difference between the two spin sublevels of the lowest Landau level. While the tunneling current-voltage characteristic at filling factor $\nu =1\mathrm{/}2$ is a single peak shifted from zero bias by a Coulomb pseudogap, the spectrum at $\nu =3\mathrm{/}2$ shows a well-resolved double peak structure. This difference is present regardless of whether $\nu =1\mathrm{/}2$ and $\nu =3\mathrm{/}2$ occur at the same or different magnetic fields. No analogous effect is seen at $\nu = 5/2$ and 7/2 in the first excited Landau level.