Doping Dependent Density of States and Pseudogap Behavior inLa2−xSrxCuO4

We have made a high-resolution photoemission study of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ 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 ( $\mu$) 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.