Electron-phonon coupling and polarons in the parent cuprate La₂CuO₄ from first-principles calculations

In the parent (undoped) phases of high-Tc cuprate superconductors, there is abundant experimental evidence for strong electron-phonon (e-ph) interactions, which result in broad photoemission spectra. The microscopic origin of these strong e-ph interactions in cuprates is not fully understood and their quantitative modeling remains challenging. In this talk, we will present first-principles e-ph calculations in the parent-compound lanthanum cuprate (La₂CuO₄, LCO) based on Hubbard-corrected density functional theory. Our calculations identify two classes of longitudinal optical (LO) phonons strongly coupled with hole states in LCO. Their energies (50-80 meV) are consistent with spectral signatures in photoemission experiments on doped cuprates. The associated electronic spectral functions in the valence band, obtained with a finite-temperature cumulant approach to describe high-order e-ph interactions, exhibit a significant broadening as well as satellite peaks due to polaron effects. The main features of the electron self-energy measured in angle-resolved photoemission spectroscopy (ARPES) are well reproduced in our calculations. Our results provide a quantitative evidence for strong e-ph interactions in parent cuprates and refine existing models by showing the importance of nonbonding orbitals and coupling with apical oxygen lattice vibrations.