Fragile Pressure-Induced Magnetism in FeSe Superconductors with a Thickness Reduction.

The emergence of high transition temperature () superconductivity in bulk FeSe under pressure is associated with the tuning of nematicity and magnetism. However, sorting out the relative contributions from magnetic and nematic fluctuations to the enhancement of remains challenging. Here, we design and conduct a series of high-pressure experiments on FeSe thin flakes.