Geometry of Landau orbits in the absence of rotational symmetry

Abstract: The integer quantum Hall effect (IQHE) is usually modeled using Galilean-invariant or rotationally-invariant Landau levels. However, these are not generic symmetries of electrons moving in a crystalline background, even in the low-density continuum limit. We present a treatment of the IQHE which abandons the Galilean dispersion relation while keeping inversion symmetry. We define an emergent metric $g^n_{ab}$ for each Landau level with a reformulation of the Hall viscosity. The metric is then used to define a guiding-center coherent state and the wavefunctions are holomorphic functions of $z^*$ times a Gaussian. By numerically studying cases with quartic dispersion, we show that the number of the zeroes of the wavefunction encircled by the semiclassical orbit, denoted by $n$, defines a "topological spin" $s_n$ by $s_n=n+\frac{1}{2}$, with its original definition as an "intrinsic angular momentum" no longer valid without rotational symmetry. At the end of the paper we show our results for the density and current responses which differentiate between diagonal and Landau-level-mixing terms. In conclusion, this treatment extracts topological information without resort to Galilean or rotational symmetry, and also reveals more generic geometric structures.