Constituents of the Quasiparticle Spectrum Along the Nodal Direction of High-$T_c$ Cuprates

Applying the Kramers-Kronig consistent procedure, developed earlier, we investigate in detail the formation of the quasiparticle spectrum along the nodal direction of high-$T_c$ cuprates. The heavily discussed “70 meV kink” on the renormalized dispersion exhibits a strong temperature and doping dependence when purified from structural effects such as bilayer splitting, diffraction replicas, etc. This dependence is well understood in terms of fermionic and bosonic constituents of the self-energy. The latter follows the evolution of the spin-fluctuation spectrum, emerging below some doping dependent temperature and sharpening below $T_c$, and is mainly responsible for the formation of the kink in question.

Figure 1

Photoemission spectra for an optimally doped Bi-2212 measured at 30 K (a), and 120 K (b), and an overdoped LSCO measured at 40 K (c)—the yellow curves show MDCs at $E_F$; (d) some examples of experimental dispersions for OP Bi-2212 to illustrate a vanish of the kink with rising the temperature—the dashed line represents the bare dispersion.

Figure 2

(a), (b) Self-energy functions derived from experimental data for an overdoped, underdoped, and optimally doped Bi-2212 samples; the inset on (a) shows the data for OD75 taken $\approx 0.15{\AA }^{-1}$ away from the node to monitor the gap opening; on (b) the solid curve shows a fit of ${\Sigma }^{\prime }(30\mathrm{K})-{\Sigma }^{\prime }(120\mathrm{K})$ to a Gaussian. (c), (d) The evolution of the kink parameters with hole concentration and temperature; different points correspond to different samples; the error bars are derived from a number of measurements of each sample.

Figure 3

Schematic summary of the temperature evolution of the real (bottom) and imaginary (top) parts of the self-energy based on the data for the optimally doped sample.