Quasi-one-dimensional Hall physics in the Harper-Hofstadter-Mott model

We study the ground-state phase diagram of the strongly interacting Harper-Hofstadter-Mott model at quarter flux on a quasi-one-dimensional lattice consisting of a single magnetic flux quantum in $y$-direction. In addition to superfluid phases with various density patterns, the ground-state phase diagram features quasi-one-dimensional analogues of fractional quantum Hall phases at fillings $\nu =1\mathrm{/}2$ and $3\mathrm{/}2$, where the latter is only found thanks to the hopping anisotropy and the quasi-one-dimensional geometry. At integer fillings

• where in the full two-dimensional system the ground-state is expected to be gapless - we observe gapped non-degenerate ground-states: At $\nu =1$ it shows an odd ‘fermionic’ Hall conductance, while the Hall response at $\nu =2$ consists of the transverse transport of a single particle-hole pair, resulting in a net zero Hall conductance. The results are obtained by exact diagonalization and in the reciprocal mean-field approximation.