Robust spin and charge excitations throughout the high-Tc cuprate phase diagram from incipient Mottness

The generic phase diagram of lightly hole doped high-T-c-cuprates hosts an antiferromagnetic insulating phase with well-defined spin-wave excitations. Contrary to the weak-coupling prediction, these modes persist up to the overdoped metallic regime as intense and dispersive paramagnons. Here we report on our study of the low-energy magnetic and charge excitations within the extended Hubbard model at strong coupling, using a modified 1/N expansion method with a variational state serving as the saddle point solution. Despite clear separation of magnetic and Hubbard-U energy scales, we find that incipient Mottness affects qualitatively dispersions and widths of magnetic modes throughout the entire phase diagram. The obtained magnetic and charge dynamical structure factors agree semiquantitatively with recent resonant x-ray and neutron scattering data for La2-xSrxCuO4 and (Bi, Pb)(2)(Sr, La)(2)CuO6+delta at all available doping levels. The weak-coupling random-phase approximation fails already for underdoped samples, pointing to the nontrivial intertwining of distinct energy scales in cuprate superconductors. The existence of a discrete charge mode which splits off the electron-hole continuum is also predicted.