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 ν=1/2 is a single peak shifted from zero bias by a Coulomb pseudogap, the spectrum at ν=3/2 shows a well-resolved double peak structure. This difference is present regardless of whether ν=1/2 and ν=3/2 occur at the same or different magnetic fields. No analogous effect is seen at ν=5/2 and 7/2 in the first excited Landau level.