Quasiparticle Line Shape of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and Its Relation to Anisotropic Transport

The bulk-representative low-energy spectrum of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ can be directly measured by angle-resolved photoemission. We find that the quasiparticle spectral line shape of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ is sensitive to both temperature and momentum. Along the $(0,0)\mathrm{\text{−}}(\pi ,0)$ direction, both $\gamma$ and $\beta$ bands develop a sharp quasiparticle peak near $k_F$ at low temperatures, but as the temperature increases the spectra quickly lose coherent weight and become broad backgrounds above $\sim 130\mathrm{K}$, which is the metal-nonmetal crossover temperature, $T_M$, in the $c$-axis resistivity. However, spectra along the $(0,0)\mathrm{\text{−}}(\pi ,\pi )$ direction evolve smoothly across $T_M$. A simple transport model can describe both in-plane and $c$-axis resistivity in terms of the quasiparticle line shape. Comparisons are also made to the cuprates, with implications for two dimensionality, magnetic fluctuations, and superconductivity.

Figure 1

Photon energy dependence of ARPES spectra along $\Gamma \mathrm{\text{−}}M$. Intensity plots for (a) 21.2 eV photons, (b) 32 eV photons on a fresh surface, and (c) 32 eV photons on an aged surface. (d) Comparison of spectra at 32 eV fresh (solid lines), 32 eV aged (thick dashed lines), and 21.2 eV (thin dashed lines) at four locations marked in the intensity plots.

Figure 2

Temperature dependence of spectra at the three FSCPs: $A$, $B$, and $C$ (see the insets). (a) Comparison of spectra between $A$ and $B$. (b) Comparison of spectra between $A$ and $C$. The insets show measurement locations in the Brillouin zone.

Figure 3

(a) Example fits extracting Lorentzian coherent peaks from spectra at point $A$. (b) QP linewidth $\Gamma$ and coherence ratio $Z/Z_0$ for points $A$ and $C$ (results from point $B$ are almost identical to $A$). Calculated and experimental resistivity is plotted for (c) the in-plane and (d) the $c$ axis. The effect of energy resolution is removed from the linewidth in the calculation.

Figure 4

Comparison of spectra at different temperatures for slightly underdoped Bi2212 and ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ at FS crossing points (a) along the $(0,0)\mathrm{\text{−}}(\pi ,\pi )$ direction and (b) near $(\pi ,0)$.