Resistance Spike Enhancement at a Landau Level Crossing in a Two- subband 2D Electron System with a 1D Density Modulation

When two Landau levels with different indices, subband, orbital, or spin, cross at the Fermi level, a resistance spike is often seen at low temperatures, signaling a ferromagnetic quantum Hall effect transition. The spike is believed to be a manifestation of extra dissipation at the boundary between the domains of quantum Hall states with different pseudo-spin. Here we report magneto-transport measurements in a two-subband 2D electron system (40 nm-wide GaAs quantum well with n $=$ 2.7 x 10$^{\mathrm{11}}$ cm$^{\mathrm{-2}})$ where a resistance spike is seen near $\nu =$ 6 at a crossing of Landau levels with different subband indices at temperatures ranging from 600 mK to 1 K. In our experiments, we impose a strain-induced, 1D periodic density modulation through the piezoelectric effect of stripes of negative e-beam resist placed on the sample surface. The data reveal a significant amplification of the resistance spike at $\nu =$ 6. We also observe that the level of enhancement depends the period of the stripes; the stripes with a 225 nm period give the strongest enhancement and lower the temperature onset to below-300 mK. We discuss possible implications of the observations.