Fine details of the nodal electronic excitations inBi2Sr2CaCu2O8+

Abstract

Very high energy resolution photoemission experiments on high quality samples of optimally doped Bi2Sr2CaCu2O 8+δ show new features in the low-energy electronic excitations. A marked change in the binding energy and temperature dependence of the near-nodal scattering rates is observed near the superconducting transition temperature, TC. The temperature slope of the scattering rate measured at low energy shows a discontinuity at TC. In the superconducting state, coherent excitations are found with the scattering rates showing a cubic dependence on frequency and temperature. The superconducting gap has a d-wave magnitude with negligible contribution from higher harmonics. Further, the bi-layer splitting has been found to be finite at the nodal point.PACS numbers: 71.27.+a, 78.20.Bh, 79.60.Bm High temperature superconductivity continues to present some of the biggest challenges in materials science today. What is the nature of the low energy excitations and what is the pairing mechanism that leads to the superconductivity? In attempting to answer these questions, angle-resolved photoemission spectroscopy (ARPES), with high resolution in both energy and momentum, has emerged as one of the leading techniques for the study of strongly correlated materials, including the high T C superconductors. Indeed, the demonstration that the k−dependence of the amplitude of the superconducting gap in these materials is consistent with d−wave symmetry represents an important contribution of the technique to the field [1]. More recently, it has been shown that ARPES is an excellent probe of the single particle self-energy a quantity that reflects the QP's interactions within the system and manifests itself in a renormalization of the single-particle dispersion and structure in the spectral width [2]. The discovery of the mass renormalization or "kink" in the dispersion in Bi 2 Sr 2 CaCu 2 O 8+δ has lead to renewed speculation about the origin of high temperature superconductivity (HTSC) and the possibility that the observed renormalization reflects coupling to some boson involved in the pairing [3]. Indeed, the "kink" has become one of the central issues in subsequent ARPES work, with considerable controversy regarding its source [1,4,5,6,7]. Is it related to the presence of spin excitations or does it reflect an interaction with phonons or indeed any other collective mode? Note that this is not an easy issue to resolve as the various energy scales are nearly identical. Our earlier studies of the doping and momentum dependence pointed to spin fluctuations [6], while some papers favour phonons [1,5] as the source of mass enhancement. A second important question that remains open is the detailed k−dependence of the superconducting gap ∆(k).Although the momentum dependence of the gap amplitude was one of the first ARPES contributions to the field, [1] the k−dependence from the near-nodal region has not previously been measured with sufficient precision. Early work showed that the contribution of higher d−wave harmonics grew as the ...

Evidence for unusual superconducting correlations coexisting with stripe order inLa1.875Ba0.125CuO4

“…134 ͒ The changes observed in ab are consistent with the idea that the near-nodal states are essential for establishing the phase coherence. 135,136 This behavior also seems consistent with the two-gap behavior that has been identified in underdoped cuprates, 137,138 in which the d-wave-like gap in the near-nodal region can extrapolate to a smaller energy than the gap observed for the antinodal states. It would be quite interesting to see with photoemission whether a gapless nodal arc 139,140 of electronic states is present at the Fermi level for T Ͼ T so .…”

High-Energy Kink Observed in the Electron Dispersion of High-Temperature Cuprate Superconductors

“…Because of these changes, the quasiparticle self-energies at low energies are also temperature dependent as shown in Fig. 3(a) for optimally doped BSCCO and in general agreement with previous experiments [6,21,22].…”

Energy scale directly related to superconductivity in high-Tccuprates: Universality from the temperature-dependent angle-resolved photoemission of Bi2Sr

“…One can see that the QPW (HWHM) denoted as Γ increases with temperature. An early ARPES study [26] has shown that the QPW around the node in the normal state is proportional to temperature T as a fingerprint of marginal Fermi liquid [27]. Within the experimental resolution of ARPES, Γ versus T is consistent with Γ ∝ T .…”