engleski

Effects of Sr and Zn doping on the metallicity and superconductivity of LSCO and YBCO

Sr doping in La2CuO4 is investigated by a Kohn-Sham DFT+U calculation. We confirm earlier calculations finding that the Sr charge remains highly localized. The bulk of the charge observed in ARPES is delocalized in situ in the CuO2 plane. We find that a selective shift of the vH singularity in energy, accounting for the failure of the rigid-band picture, is a dielectric effect of doping. We show that Kohn-Sham DFT+U reproduces the observed Fermi-surface arcs, when not restricted to the paramagnetic solution space. Substituting planar Cu by isotopically pure 67Zn in YBCO, we measure the NQR signal on the Zn site itself for the first time. We find that Zn creates large insulating islands, extending at least to the nearest-neighbor Cu site, thus confirming that doping induces an orbital delocalization transition in the plane, which is locally reversed by Zn substitution. Calculations show that the D4 symmetry-breaking observed in NQR is due to the same partial lifting of degeneracy of the nearest-neighbor oxygen sites as in the LTT transition in LSCO.

high-temperature superconductors; doping; NQR; DFT

Plenarno predavanje na konferenciji Superstripes 2014 ; Erice, Italija, 25.-31.07.2014.