Speaker
Description
In double-layer quantum Hall systems, collective modes represented by odd integer quantum Hall states are driven by the competition between interlayer and intralayer Coulomb interactions. However, such unusual quantum Hall states are only available at sub-kelvin temperatures owing to weak interlayer Coulomb interactions. Here, we report stable odd integer quantum Hall states, $\nu_{tot}$ = -1 and -3, up to approximately 10 K in twisted double bilayer graphene whose interlayer distance is just sub-nanometer scale. Unlike layer coherent states in GaAs double-layers, odd integer quantum Hall states appear particularly at n = 1 orbital in twisted double bilayer graphene. In our twisted double layers, an extra meron-antimeron interaction, especially at n = 0 orbital, overwhelms the electron-hole interaction. Thus, excitonic condensation is missing at n = 0 orbital. We also observed a rich quantum Hall transition with external electric fields, which can control the layer and orbital degree of freedom. In addition, in the n = 1 orbital, we found signatures of a pair of conventional electrons and a Majorana quasiparticle.
