With the arrival of new experimental, numerical and theoretical techniques, the discovery of new materials and new processes has multiplied in recent decades. Condensed matter has diversified, but also became more intricate as the processes in some materials turned out to be quite entangled. The aim of this thesis is to show that beyond complex phenomena governing the single-layer ruthenate Sr2RuO4 and the mercury-based high-TC HgBa2CuO4+x, low-energy electronic properties can be universal. The Fermi-liquid theory is the finest example: its description and its application allow to create a background upon which deviations can be much better recognized.