engleski

ARPES spectra of hole- and electron-doped superconductors

We propose that observed ARPES spectra in optimally doped superconducting BSCCO and NCCO are generically due to the same mechanism, interaction with dispersive paramagnons. The interaction is in the opposite physical regime in the two cases. In BSCCO, Tc is below the paramagnon band-edge, taken at the observed resonance energy of 41 meV. In NCCO, Tc is above the characteristic temperature of fast AF fluctuations, about 10 K in muon experiments. Thus the BSCCO pseudogap below Tc is due to zero-point paramagnon fluctuations, while in NCCO the paramagnons are semiclassical even below Tc. The ARPES response in BSCCO suddenly changes at Tc. We explain that by another regime change, of the paramagnon damping, which goes from underdamped to overdamped when BSCCO enters the normal state. The narrow antinodal peak in superconducting BSCCO consists of electrons in the antiadiabatic regime, which are so slow around the vH point that they do not scatter off the paramagnons, so their spectral intensity survives in the middle of the pseudogap. The narrow peak disappears because antiadiabatic conditions are not met further away from the vH point, not because of the Fermi function cutoff, and it is strictly speaking not a quasiparticle. Its leading edge scale is set by the chemical potential and exists even in the absence of a superconducting gap. In NCCO the antiadiabatic peak is negligible, while the wide dispersing features are incoherent, analogous to the BSCCO hump, and disappear near the Fermi energy because of pseudogap suppression, again unrelated to the Fermi cutoff. Thus both optimally doped BSCCO and NCCO are in fact pseudogapped, which we propose as the generic situation for doped perovskites. An additional outcome of these investigations is that the effective oxygen-oxygen hopping appears even larger in NCCO than in BSCCO, so it is significantly greater than the effective copper-oxygen hopping in both cases.

ARPES; pseudogap; high-Tc; superconductivity

nije evidentirano