Double transfer through Dirac points in a tunable honeycomb optical lattice

TL;DR

This study investigates Bloch-Zener oscillations of ultracold fermions in a tunable honeycomb lattice, revealing a double-peak transfer feature through two Dirac points, consistent with a Landau-Zener model.

Contribution

It demonstrates the observation of double transfer peaks through Dirac points in a tunable optical lattice, supported by analytical and numerical models.

Findings

Double-peak feature in transferred fraction to the second band.

Good agreement with Landau-Zener transition model.

Absence of St"uckelberg oscillations due to harmonic confinement.

Abstract

We report on Bloch-Zener oscillations of an ultracold Fermi gas in a tunable honeycomb lattice. The quasi-momentum distribution of the atoms is measured after sequentially passing through two Dirac points. We observe a double-peak feature in the transferred fraction to the second band, both as a function of the band gap at the Dirac points and the quasi-momentum of the trajectory. Our results are in good agreement with a simple analytical model based on two successive Landau-Zener transitions. Owing to the variation of the potential gradient over the cloud size, coherent St\"uckelberg oscillations are not visible in our measurements. This effect of the harmonic confinement is confirmed by a numerical simulation of the dynamics of a trapped 2D system.