Single-Particle Spectrum in the Electron-Doped Cuprates

We study the evolution of the single-particle spectrum with electron doping in a scheme which adds multiple exchange of transverse spin excitations to the mean-field antiferromagnetic insulator. Away from half-filling small Fermi surface pockets appear first around the $X$ points, and simultaneously new spectral weight grows in the insulating gap. With further doping the in-gap states develop the character of a renormalized quasiparticle band near the chemical potential. The essential features in momentum-energy space agree well with recent studies using angle-resolved photoemission spectroscopy on electron-doped cuprates. We interpret the origins and the nature of the in-gap states using a simple variational wave function.

Figure 1

The doping dependence of the DOS. Sharp quasiparticle peaks appear at the edges of the insulating gap with broad incoherent backgrounds of width $\sim 8t$. Away from half-filling, the spectral weight transfers particularly from the lower band to the in-gap states at $\omega -\mu \sim -t$. The chemical potential lies in the upper quasiparticle band.

Figure 2

The contour plot for the spectral intensity $A(\mathit{k},\omega )$ along the high-symmetry lines of the Brillouin zone. The quasiparticle band appears at the bottom (top) of the upper (lower) band for $n={1.00}^{+}$. The AF shadow bands with rather weak intensity appear along $X\mathrm{\text{−}}\Gamma \mathrm{\text{−}}{M}^{\prime }$ ($M^{\prime }\mathrm{\text{−}}M\mathrm{\text{−}}X$) in the upper (lower) band. Upon doping, the in-gap states at $\omega -\mu \sim -t$ together with the upper quasiparticle band acquire the features of a renormalized quasiparticle band similar to that in the paramagnetic phase.

Figure 3

The spectral intensity along the $\Gamma (0,0)\mathrm{\text{−}}M(\pi ,\pi )$ line. As the doping increases, the in-gap states develop and become dispersive. The in-gap states and the upper quasiparticle band exhibit features of a renormalized quasiparticle band similar to that in the paramagnetic phase.

Figure 4

The contour plot of $A(\mathit{k},0)$ at the chemical potential corresponding to a Fermi-surface plot. Upon doping, the small Fermi surface pockets appear first around the $X$ points. As the doping increases, these pockets deform and become pieces of the paramagneticlike Fermi surface indicated by the dashed line for $n=1.12$.

Figure 5

The comparison of the quasihole dispersions for $n=1.12$: (a) evaluation by the variational wave function (green) and the MF energy (red), and (b) results of the SCBA calculation in the quasiparticle $\gamma$ representation.