Pseudogap in Cuprates: Electron-Hole Asymmetry as seen by Infrared Spectroscopy
CNRS (UPR5) - ESPCI, Physique du Solide, 10 rue Vauquelin, 75005 Paris (France)
Identifying how remote high critical temperature superconductors are from conventional metals is an important clue for these materials. Infrared spectroscopy can provide a model independent insight about the properties of these “strange metals”. Indeed the optical conductivity integrated up to a set of cut-off frequencies (spectral weight) has clear signatures when studied versus temperature and cut-off frequency, for a metal (full Fermi surface) or a partially gapped state.
I will present our data deduced from in-plane reflectivity measurements, in electron doped cuprates (Pr2-xCexCuO4, x=0.11, 0.13, 0.15, 0.17) and in hole doped materials (single layer slightly underdoped HgBa2CuO8+d, two layers underdoped Bi2Sr2CaCuO8+d cuprates).
Above Tc, all overdoped samples exhibit conventional metallic metals. We find a clear spectroscopic signature of the onset of a (magnetic, high energy) “pseudogap” up to x=0.15 (optimal doping) in the electron doped cuprates. In contrast, the pseudogap is hardly seen in the in-plane conductivity of hole doped cuprates.
Below Tc, the superconducting state also reveals some conspicuous differences between both families.