Crossover region between nodal and antinodal states at the Fermi level of optimally doped and overdopedBi2Sr1.6Nd0.4

Abstract

We have studied Bi2Sr1.6Nd0.4CuO 6+δ using Angle Resolved Photoemission Spectroscopy in the optimal and overdoped regions of the phase diagram. We identify a narrow crossover region in the electronic structure between the nodal and antinodal regions associated with the deviation from a pure d-wave gap function, an abrupt increase of the quasiparticle lifetime, the formation of Fermi arcs above Tc, and a sudden shift of the bosonic mode energy from higher energy, ∼60meV, near the nodal direction, to lower energy, ∼20meV, near the antinodal direction. Our work underscores the importance of a unique crossover region in the momentum space near EF for the single layered cuprates, between the nodal and antinodal points, that is independent of the antiferromagnetic zone boundary.Understanding the near-E F electronic band structure is essential to making sense of the superconducting cuprate phase diagram. Increasingly, studies on these systems are suggesting that the Fermi surface (FS) may be better thought of as divided into regions along. For example, the partial gapping of the FS in the pseudogap (PG) phase results in the unusual formation of ungapped regions which appear as disconnected arcs or "Fermi Arcs" (FA [18]. STM work has suggested another potential crossover region on the Fermi surface associated with the antiferromagnetic zone boundary, characterized by the disappearance of the coherent quasiparticle (QP) peak [19]. Also, bosonic modes which introduce "kinks" in the near-E F band structure may define a key region of the FS. Recent work finds a shift in the kink energy towards low binding energy correlated with the softening of the Cu-O bond stretching (BS) phonon at a critical FS nesting wavevector [20]. Finally, recent quantum oscillation data [21][22] have suggested that the FS is indeed separated into hole and electron pockets providing another crossover region for the low energy QP. Although controversial, evidence for an hole pocket on the FS has been recently provided by photoemission experiments [23]. Thus, it is increasingly important that we continue to explore • ±1• away from the nodal point. (c) Leading edge gap data for both SC and PG phases. Here the violet region is shifted to include the expected FA scaling for T=40K (indicated by the brown line).

Large momentum-dependence of the main dispersion ‘kink’ in the high-Tcsuperconductor Bi2Sr2CaCu2O8+δ

“…The findings in figure 1 contrast with a previous study of overdoped Pb-Bi2212 where it was argued that the scattering rate near E F is independent of k [22]. We also point out that these results contradict recent claims that the energy kink is constant near the node and then suddenly jumps at a 'crossover' point on the FS ∼ 15 • away from the node [23,24], though there still may be a crossover parameterized by, e.g. the intensity and sharpness of the features in eff (ω, θ), as seen in figures 1(e) and (f).…”

Large momentum-dependence of the main dispersion "kink" in the high-Tc superconductor Bi2Sr2CaCu2O8+δ

“…The findings in Figure 1 contrast with a previous study of overdoped Pb-Bi2212 where it was argued that the scattering rate near E F is independent of k [22]. We also point out that these results contradict recent claims that the energy Ω kink is constant near the node and then suddenly jumps at a "crossover" point on the FS ∼ 15 • away from the node [23,24], though there still may be a crossover parameterised by, e.g., the intensity and sharpness of the features in Σ eff (ω, θ), as seen in Figure 1(e)-(f).…”