ELECTRONIC STATES IN LA2-XSRXNIO4 (X = 0 TO 1.20) INVESTIGATED BY SCANNING TUNNELING SPECTROSCOPY

Using scanning tunneling spectroscopy (STS), the doping dependence of the density of states (DOS) on La2-xSrxNiO4 thin films is investigated and the results are compared to that of La2-xSrxCuO4. In the nickelat e system, as the carrier concentration increases, the DOS around the F ermi energy gradually appears with tailing both from the edges of the conduction band and the valence band. The energy-gap structure of La2- xSrxNiO4 remains unchanged up to relatively high carrier concentration s as compared to that of La2-xSrxCuO4. Especially, in the composition range of x < 0.5, the STS spectra of Ni-system are almost independent of the Sr concentration. On the other hand, in the heavy carrier-doped region,the DOS shape of La0.8Sr1.2NiO4 becomes similar to that of met allic La1.85Sr0.15CuO4. (C) 1997 Elsevier Science B.V.