Interaction effects on a topological spin pump*

We investigate the influence of the Hubbard interaction between spinful fermions in a one-dimensional topological spin pump using both exact diagonalization and DMRG simulations. The spin pump is realized by two Rice-Mele models for the spin components, whose parameter are varied in an adiabatic, cyclic and spin-dependent way preserving total time-reversal symmetry.

In the absence of interactions the system is characterized by opposite, nontrivial spin Chern numbers whose difference is a Z_2 topological invariant. This gives rise to a quantized counter-propagating spin transport. With repulsive interactions the spin transport remains intact even for large interaction strengths. On the other hand it's quickly destroyed by attractive interactions in magnitudes of the tunneling processes. At the same time the spin Chern numbers calculated from the winding of spin polarizations remain non-trivial for a much larger range of interactions. We show that the dynamics of the spin pump is well captured for moderate interaction strength by an effective mean-field model of the two individual spin components and taking into account quantum fluctuations as a heating process. The strong interaction limit can be described by an effective model.