Transfer of spectral weight across the gap of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ induced by La doping

We study with angle-resolved photoelectron spectroscopy the evolution of the electronic structure of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, when holes or electrons are introduced, through Rh or La substitutions. At low dopings, the added carriers occupy the first available states, at the bottom or top of the gap, revealing an asymmetric gap of 0.7 eV, in good agreement with scanning tunnel microscope measurements. At further doping, we observe a reduction of the gap and a transfer of spectral weight across the gap, although the quasiparticle weight remains very small. We discuss the origin of the in-gap spectral weight as a local distribution of gap values.

Figure 1

(a) In-plane resistivity in zero magnetic field and (b) magnetization at 1 T, measured for the main samples studied in this Rapid Communication: pure ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, La1 (1.5% La), La2 (4% La), and Rh1 (15% Rh).

Figure 2

(a) Energy positions of the $J=1/2$ peak at $X$ (blue points) and $J=3/2$ peak at $\mathrm{\Gamma }$ (red points) measured around 50 K for different samples of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ (middle), ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ doped with Rh (left) and La (right). The axis roughly corresponds to different dopings, ranging 10–$15\%$ in the case of Rh and 1–$4\%$ in the case of La. (b) Sketch of the shift of the chemical potential with initial doping. As the $J=1/2$ band is gapped, it is divided into a lower band (LB) and an upper band (UB).

Figure 3

First column: Energy-momentum plots in the $\mathrm{\Gamma }X$ direction. Red and blue lines are guides for the eye for the dispersion of $J=3/2$ and $J=1/2$ bands. Second column: Energy distribution curve (EDC) at $\mathrm{\Gamma }$ for the $J=3/2$ band. Third column: EDC at $X$ [${\mathrm{k}}_F$ for (b3)] for the $J=1/2$ band. Fourth column: Spectral weight integrated at $-20$ meV in a 50-meV window. The black square corresponds to the two-Ir Brillouin zone (BZ) and the dotted black square to the one-Ir BZ. Fifth column: Sketch of the position of the main bands. The rows correspond to different samples (see Fig. 1): (a) pure, (b) Rh1, (c) La1, and (d) La2. All data were acquired at 100 eV and horizontal polarization, except for Rh1 acquired at 70 eV and vertical polarization. The temperature was 50 K.

Figure 4

(a) Energy-momentum plot along $\mathrm{\Gamma }M$ measured for La2 at 50 K. Blue (red) lines indicate the dispersion for $J=1/2$ (3/2) bands. (b) Dispersion extracted from (a) by MDC analysis. The size of the markers correspond to the amplitude of the peak. (c) Zoom near the Fermi level in the $MM$ direction. (d) EDC at $M$ extracted from (c).