Kinks, Nodal Bilayer Splitting, and Interband Scattering in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$

We apply the new-generation angle-resolved photoemission spectroscopy methodology to the most widely studied cuprate superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$. Considering the nodal direction, we found noticeable renormalization effects known as kinks both in the quasiparticle dispersion and scattering rate, the bilayer splitting, and evidence for strong interband scattering—all the characteristic features of the nodal quasiparticles detected earlier in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$. The typical energy scale and the doping dependence of the kinks clearly point to their intimate relation with the spin-1 resonance seen in the neutron scattering experiments. Our findings strongly suggest a universality of the electron dynamics in the bilayer superconducting cuprates and a dominating role of the spin fluctuations in the formation of the quasiparticles along the nodal direction.

Figure 1

Raw ARPES photoemission intensity measured using three different photon energies as a function of angle and kinetic energy of the photoelectrons. The inset schematically shows the LDA-predicted Fermi surface and a cut in the $k$ space along which the data have been taken.

Figure 2

Positions of the MDC’s maxima (a) and their widths (b) as a function of binding energy for the UD35 sample. Dashed curves are fits to the low energy data. Black and gray arrows mark the energy positions of the low and high energy “kinks,” respectively. Insets show exemplary MDC and EDC.

Figure 3

Dispersion as a function of doping. Horizontal lines mark the energies of the kink, where dispersion starts to deviate from the straight line. Gray arrows show the position of the second high energy kink. Momentum scales are matched by putting $k_F=1{\AA }^{-1}$.

Figure 4

(a),(b) Constancy of the nodal bilayer splitting. Solid lines are experimental dispersions. (c) Intensity map taken 10° away from the nodal direction in the OD90 sample. Solid yellow curves are the MDCs corresponding to the binding energies marked by black arrows. (d) Widths of the MDCs from panel (c).