Angle-Resolved Photoemission Spectroscopy of the Antiferromagnetic Superconductor ${\mathrm{N}\mathrm{d}}_{1.87}{\mathrm{C}\mathrm{e}}_{0.13}{\mathrm{C}\mathrm{u}\mathrm{O}}_4$: Anisotropic Spin-Correlation Gap, Pseudogap, and the Induced Quasiparticle Mass Enhancement

We performed high-resolution angle-resolved photoemission spectroscopy on ${\mathrm{N}\mathrm{d}}_{1.87}{\mathrm{C}\mathrm{e}}_{0.13}{\mathrm{C}\mathrm{u}\mathrm{O}}_4$, which is located at the boundary of the antiferromagnetic (AF) and the superconducting phase. We observed that the quasiparticle (QP) effective mass around $(\pi ,0)$ is strongly enhanced due to the opening of the AF gap. The QP mass and the AF gap are found to be anisotropic, with the largest value near the intersecting point of the Fermi surface and the AF zone boundary. In addition, we observed that the QP peak disappears around the Néel temperature ($T_N$) while the AF pseudogap is gradually filled up at much higher temperatures, possibly due to the short-range AF correlation.

Figure 1

Plot of near-$E_F$ ARPES intensity at 30 K integrated within 25 meV with respect to $E_F$ and symmetrized with respect to the $(0,0)\mathrm{\text{−}}(\pi ,\pi )$ nodal line. Arrows denoted by a–f show cuts where detailed ARPES measurements shown in Fig. 2 were done.

Figure 2

Upper panel: ARPES spectra of NCCO ($x=0.13$) measured at 30 K along several cuts parallel to the $(0,0)\mathrm{\text{−}}(\pi ,\pi )$ direction shown by arrows in Fig. 1. Blue spectra are at the Fermi surface. Lower panel: ARPES-intensity plot as a function of the wave vector and binding energy, showing the experimental band dispersion. Peak positions in ARPES spectra are shown by bars and dots.

Figure 3

Schematic diagram to explain how the QP dispersion is modified by the AF correlation for three different cases. In case I, the original QP band (thin solid line) and the shadow band (thin broken line) intersect each other below $E_F$. In cases II and III, the intersecting point is at and above $E_F$, respectively. Thick solid lines show the QP dispersions modified by the AF correlation.

Figure 4

Temperature dependence of the ARPES spectrum of NCCO ($x=0.13$) measured at a point on the Fermi surface shown by a filled circle in the inset, where the PDH structure is clearly observed. The solid straight lines on the spectra show the linear fits to the high-energy region (0.2–0.5 eV).