Drude weight increase by orbital and repulsive interactions in fermionic ladders

TL;DR

This paper demonstrates that in fermionic ladder systems, orbital and repulsive interactions can increase the Drude weight, contrary to one-dimensional systems, with implications for ultracold atoms and topological states.

Contribution

It reveals that in quasi-one-dimensional ladders, interactions can enhance the Drude weight, a novel effect not seen in strictly 1D systems, using bosonization and MPS methods.

Findings

Drude weight increases with repulsive interactions in ladders.

Orbital and magnetic flux effects bias scattering processes.

Results applicable to ultracold atoms and topological edge states.

Abstract

In strictly one-dimensional systems, repulsive interactions tend to reduce particle mobility on a lattice. Therefore, the Drude weight, controlling the divergence at zero-frequency of optical conductivities in perfect conductors, is lower than in non-interacting cases. We show that this is not the case when extending to quasi one-dimensional ladder systems. Relying on bosonization, perturbative and matrix product states (MPS) calculations, we show that nearest-neighbor interactions and magnetic fluxes provide a bias between back- and forward-scattering processes, leading to linear corrections to the Drude weight in the interaction strength. As a consequence, Drude weights counter-intuitively increase (decrease) with repulsive (attractive) interactions. Our findings are relevant for the efficient tuning of Drude weights in the framework of ultracold atoms trapped in optical lattices and equally affect topological edge states in condensed matter systems.