Doping dependent density of states and pseudogap behavior in La_1−xSr_xCuO₄

We have made a high-resolution photoemission study of La_1−xSr_xCuO₄ in a wide hole concentration (x) range from a heavily overdoped metal to an undoped insulator. As x decreases, the spectral density of states at the chemical potential (μ) is suppressed with an x dependence similar to the suppression of the electronic specific heat coefficient. In the underdoped region, the spectra show a pseudogap structure on the energy scale of 0.1 eV. The width of the pseudogap increases with decreasing x following the x dependence of the characteristic temperatures of the magnetic susceptibility and the Hall coefficient.