Correlated electron systems often host a range of phases that have comparable energy scales and can compete for the electrons or coexist with them. Archetypical examples are the electron and spin density wave states that appear in the vicinity of superconductivity in the La-based cuprate superconductors.

Nevertheless, the exact nature of these states as well as the coupling between electronic and spin instabilities has remained elusive. To attack this question, we applied uniaxial pressure to a high temperature superconductor La1.88Sr0.12CuO4. In our tour-de-force experiment we combined a newly designed pressure cell, state of the art neutron ray simulations and unique focusing capabilities of the ThALES instrument at the ILL neutron source to extract information from tiny samples.

As seen in the figure above, we found that uniaxial pressure repopulates the domains, with only one domain surviving. This effectively excludes all potential multi-q states, settles the uniaxial stripe phase as the ground state for the La-based superconductors and demonstrates the coupling between spin and charge order in these systems.

For more information, have a look at our preprint: https://arxiv.org/abs/2204.02304