# Finite-temperature properties of interacting bosons on a two-leg flux ladder

## TL;DR

This study explores how finite temperatures affect key quantum phases and observable signatures in a two-leg flux ladder system with interacting bosons, using advanced simulation methods to identify persistent features at elevated temperatures.

## Contribution

It introduces a finite-temperature analysis of vortex-fluid and Meissner phases in flux ladders, employing matrix-product-state simulations to reveal observable signatures at non-zero temperatures.

## Key findings

- Finite-momentum maxima in momentum-distribution functions persist at elevated temperatures.
- Signatures of the vortex-fluid phase weaken in local rung and chiral currents with increasing temperature.
- A crossover diagram delineates temperature ranges where phase signatures are detectable.

## Abstract

Quasi-one-dimensional lattice systems such as flux ladders with artificial gauge fields host rich quantum-phase diagrams that have attracted great interest. However, so far, most of the work on these systems has concentrated on zero-temperature phases while the corresponding finite-temperature regime remains largely unexplored. The question if and up to which temperature characteristic features of the zero-temperature phases persist is relevant in experimental realizations. We investigate a two-leg ladder lattice in a uniform magnetic field and concentrate our study on chiral edge currents and momentum-distribution functions, which are key observables in ultracold quantum-gas experiments. These quantities are computed for hard-core bosons as well as noninteracting bosons and spinless fermions at zero and finite temperatures. We employ a matrix-product-state based purification approach for the simulation of strongly interacting bosons at finite temperatures and analyze finite-size effects. Our main results concern the vortex-fluid-to-Meissner crossover of strongly interacting bosons. We demonstrate that signatures of the vortex-fluid phase can still be detected at elevated temperatures from characteristic finite-momentum maxima in the momentum-distribution functions, while the vortex-fluid phase leaves weaker fingerprints in the local rung currents and the chiral edge current. In order to determine the range of temperatures over which these signatures can be observed, we introduce a suitable measure for the contrast of these maxima. The results are condensed into a finite-temperature crossover diagram for hard-core bosons.