Anisotropic evolution of charge/spin excitations in square-planar cuprates*

Superconductivity is achieved in T'-Nd₂CuO₄ be means of oxygen annealing which injects electrons via controlled defect engineering. Here, we use Resonant Inelastic X-Ray Scattering (RIXS) to study the evolution of magnetic and charge excitations in parent and superconducting compounds. Our RIXS study reveals a hardening of the spin waves and the enhancement of charge excitations in the superconducting phase. Remarkably, the hardening of the low energy excitations is strongly anisotropic. A spectral weight redistribution between the antinodal and nodal directions is observed which brings important information on the dynamics of the superconducting state. The evolution of the low energy dynamics is then discussed in comparison with other cuprates as well as Fe-based superconductors.