Genesis of pseudogaps from electron-lattice resonances

Pseudogaps, often associated with unconventional superconductors, have long posed a challenge to condensed matter theory. Here, we discuss a possible solution to the pseudogap problem by invoking the recently developed picture of quantum acoustics, which has already succeeded in explaining some of the strange metal mysteries, such as T-linear resistivity and the displaced Drude peak. We describe lattice vibrations within the coherent state formalism, akin to Glauber states in quantum optics, which naturally suggests radically different approximations compared to Fock states, and leads to a non-perturbative treatment of the charge carriers in a dynamical deformation potential field. We find that in some materials, particularly low-(electron-)doped cuprates, acoustic and carrier bands can intersect in a range of important energies and momenta. At these junctures, a resonant coupling between carriers and the lattice takes place, destroying the underlying Fermi surfaces. This strong coupling induces the formation of gaps and can give rise to the emergence of hybrid carrier-phonon quasiparticles. Crucially, a (quantum-acoustical) pseudogap materializes when such a gapped region lies in the vicinity of the Fermi level. The patterns of these pseudogaps align with the existing ARPES data, offering a simple but appealing explanation for their emergence, grounded purely on conventional acoustic and electronic band structures.