Controlling competing orders via non-equilibrium acoustic phonons: emergence of anisotropic electronic temperature

Ultrafast perturbations offer a unique tool to manipulate correlated systems due to their ability to promote transient behaviors with no equilibrium counterpart. A widely employed strategy is the excitation of coherent optical phonons, as they can cause significant changes in the electronic structure and interactions on short time scales. Here, we explore a promising alternative route: the non-equilibrium excitation of acoustic phonons. We demonstrate that it leads to the remarkable phenomenon of a momentum-dependent temperature, by which electronic states at different regions of the Fermi surface are subject to distinct local temperatures. Such an anisotropic electronic temperature can have a profound effect on the delicate balance between competing ordered states in unconventional superconductors, opening a novel avenue to control correlated phases.