Fermiology of YBa₂Cu₄O₈

We present angle-resolved photoemission results of YBa₂Cu₄O₈ (124). The energy distribution curves are very similar to those observed in the related compound YBa₂Cu₃O₆₉ (123). The structure of the 124 compound is very similar to that of the 123, except that the 124 possesses two chain bands instead of one crossing the Fermi energy. This has an effect of lowering the density of states at E_F and making the 124 compound more stable, to oxygen content. Otherwise, their observed electronic structures are very similar, including the sharp peaks at E_F at the X and Y symmetry points, and the very sharp state at 1 eV binding energy at the S point The states at E_F along the Γ-S line exhibit the same symmetry as those in the 123, i.e. d²_x²_-y, while the states at X and Y exhibit d_xy symmetry.