  The relation between d-wave superconductivity and stripes is fundamental to
the understanding of ordered phases in cuprates. While experimentally both
phases are found in close proximity, numerical studies on the related
Fermi-Hubbard model have long been investigating whether stripes precede,
compete or coexist with superconductivity. Such stripes are characterised by
interleaved charge and spin density wave ordering where fluctuating lines of
dopants separate domains of opposite antiferromagnetic order. Here we show
first signatures of stripes in a cold-atom Fermi-Hubbard quantum simulator. By
engineering a mixed-dimensional system, we increase their typical energy scales
to the spin exchange energy, enabling us to access the interesting crossover
temperature regime where stripes begin to form. We observe extended, attractive
correlations between hole dopants and find an increased probability to form
larger structures akin to stripes. In the spin sector, we study correlation
functions up to third order and find results consistent with stripe formation.
These higher-order correlation measurements pave the way towards an improved
microscopic understanding of the emergent properties of stripes and their
relation to other competing phases. More generally, our approach has direct
relevance for newly discovered high-temperature superconducting materials in
which mixed dimensions play an essential role.
