Photoemission study of (Cu, Tl)-1223 and Tl-1223 with T-c above 130 K

A change of electronic structure and chemical bond nature of high pressure synthesized (Cu, TI)Ba2Ca2Cu3O9-delta [(Cu, TI)-1223] and TIBa2Ca2Cu3O9-del ta [TI-1223] with reduction-annealing, which leads significant rise of thei r superconducting transition temperature T,above 130 K, has been investigat ed by insitu photoemission spectroscopy, Their intrinsic surface nature has been achieved by fracturing in vacuum, In (Cu, TI)-1223, a Fermi edge is o bserved for the first time. Trivalent TI and heavily over-doped states of C u-O clusters are dominant in as-grown specimens of both systems. The anneal ing resulted in remarkable shifts of photoemission spectra of Ba and TI cor e levels towards higher binding energy with an increase of the annealing te mperature, which means a selective oxygen-depletion around their charge-res ervoirs and a decrease of valency of TI, In contrast, there are quite littl e shape-changes and movements in valence band spectra and core signals of C u and O. These results reveal that, in the high temperature-treated specime ns, major portions of the electrons left should be absorbed into the cation s in their charge reservoir, which consequently should cause a much more mo derate change of the hole-concentration of the CuO2 planes. It suggests tha t the utilization of this charge-redistribution mechanism in over-doped spe cimens should be an advantageous way to optimize the electronic structure o f the 1223 phases for high T-c.