Direct observation of incommensurate magnetism in Hubbard chains

TL;DR

This study uses ultracold fermions in optical lattices to directly observe incommensurate spin correlations in doped Hubbard chains, confirming theoretical predictions and revealing microscopic origins of magnetic phenomena.

Contribution

It provides the first direct experimental observation of incommensurate magnetism in Hubbard chains using quantum gas microscopy, aligning with Luttinger liquid theory.

Findings

Doping causes a linear shift in spin-density wave vector.

Increased polarization decreases the wave vector as predicted.

Interchain coupling leads to magnetic polaron formation.

Abstract

The interplay between magnetism and doping is at the origin of exotic strongly correlated electronic phases and can lead to novel forms of magnetic ordering. One example is the emergence of incommensurate spin-density waves with a wave vector that does not match the reciprocal lattice. In one dimension this effect is a hallmark of Luttinger liquid theory, which also describes the low energy physics of the Hubbard model. Here we use a quantum simulator based on ultracold fermions in an optical lattice to directly observe such incommensurate spin correlations in doped and spin-imbalanced Hubbard chains using fully spin and density resolved quantum gas microscopy. Doping is found to induce a linear change of the spin-density wave vector in excellent agreement with Luttinger theory predictions. For non-zero polarization we observe a decrease of the wave vector with magnetization as expected from the Heisenberg model in a magnetic field. We trace the microscopic origin of these incommensurate correlations to holes, doublons and excess spins which act as delocalized domain walls for the antiferromagnetic order. Finally, when inducing interchain coupling we observe fundamentally different spin correlations around doublons indicating the formation of a magnetic polaron.