Research news

In our recent publication Bertok et al.,PRB 106, 045141 (2022) , we investigate the splitting of topological charge pumping due to a Hubbard interaction that is introduced in a Rice-Mele pump. For a system consisting of spin up and down particles, a Rice-Mele pump transports two particles per pump cycle through the system when encircling a degeneracy in the parameter manifold. The Hubbard interaction splits this degeneracy into two separate critical points that each lead to the pumping of a single particle when being encircled. This gives an interpretation for the breakdown of topological pumping, which has recently been measured experimentally at ETH Zürich ( arXiv:2204.06561 ). Additionally, we predict an interaction-driven pumping scheme, in which particles are only pumped at finite interaction strength.
In the plot, the pumping around a single critical point at finite interaction strength is compared for three Hamiltonians that differ in the amount of symmetry they possess. All of them pump a single charge (Q) per cycle, while one of them also pumps a single spin (Qs).

In our recent study Jansen et al., Phys. Rev. B 102, 165155 (2020) , we use a density-matrix renormalization group method combined with local basis optimization to efficiently compute thermodynamic expectation values and finite-temperature spectral functions of the Holstein polaron model. Focusing on the intermediate electron-phonon coupling regime, we first test our approach by comparing the spectral function to that obtained with the finite-temperature Lanczos method. We then compute the electron-emission spectrum and the phonon spectral function. As temperature is increased, we observe that spectral weight is shifted to lower frequencies and larger momenta for the electron-emission spectrum. For the phonon spectral function, larger temperatures allow us to observe a reflected polaron band.

In our recent publication Hayward et al., Phys. Rev. A 103, 043310 (2021) , we investigate the breakdown of topological charge pumping due to static, random disorder. The amount of charge that is pumped through the system in each pump cycle is quantized to 1 for weak disorder ω/J. The critical disorder that leads to a breakdown of this quantization is determined via the most likely energy gap, the local Chern marker (LCM), the skewness γ of LCM distributions and a time-dependent calculation of the pumped charge ΔQ.