Stripes developed at the strong limit of nematicity in FeSe films

Superconductivity in one monolayer FeSe film on SrTiO₃ has attracted enormous attentions. However, the electronic behaviors of FeSe films on SrTiO₃ show extraordinary dichotomy as the superconductivity is suppressed and strong nematicity develops for the film thicker than one monolayer. On the other hand, long-range magnetism is absent, despite large local magnetic moment has been found in bulk FeSe. Here we report on low-temperature scanning tunneling microscopy studies of the multilayer FeSe films grown by molecular beam epitaxy. We find a stripe-type charge ordering instability, which develops beneath the nematic state. The emergence of stripe-type ordering indicates a magnetic fluctuation, competing with the ordinary collinear antiferromagnetic order in FeSe films. The existence of stripes in iron-based superconductor that resemble the stripe order in cuprates provides a platform to reveal the complex interactions between nematicity, magnetism and superconductivity in high-temperature superconductors.