Angle-resolved photoemission studies of the cuprate superconductors

Abstract

The last decade witnessed significant progress in angle-resolved photoemission spectroscopy (ARPES) and its applications. Today, ARPES experiments with 2 meV energy resolution and 0.2 • angular resolution are a reality even for photoemission on solid systems. These technological advances and the improved sample quality have enabled ARPES to emerge as a leading tool in the investigation of the high-Tc superconductors. This paper reviews the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds, with the purpose of providing an updated summary of the extensive literature in this field. The low energy excitations are discussed with emphasis on some of the most relevant issues, such as the Fermi surface and remnant Fermi surface, the superconducting gap, the pseudogap and d-wave-like dispersion, evidence of electronic inhomogeneity and nano-scale phase separation, the emergence of coherent quasiparticles through the superconducting transition, and many-body effects in the one-particle spectral function due to the interaction of the charge with magnetic and/or lattice degrees of freedom. Given the dynamic nature of the field, we chose to focus mainly on reviewing the experimental data, as on the experimental side a general consensus has been reached whereas interpretations and related theoretical models can vary significantly. The first part of the paper introduces photoemission spectroscopy in the context of strongly interacting systems, along with an update on the state-of-the-art instrumentation. The second part provides a brief overview of the scientific issues relevant to the investigation of the low energy electronic structure by ARPES. The rest of the paper is devoted to the review of experimental results from the cuprates and the discussion is organized along conceptual lines: normal-state electronic structure, interlayer interaction, superconducting gap, coherent superconducting peak, pseudogap, electron self energy and collective modes. Within each topic, ARPES data from the various copper oxides are presented.

Chemical potential oscillations from nodal Fermi surface pocket in the underdoped high-temperature superconductor YBa2Cu3O6+x

“…The nodal locations refer to k nodal = [π/2a, π/2a] in the Brillouin zone, and the antinodal locations refer to k antinodal = [π/a, 0] in the Brillouin zone, where a is the lattice constant. This picture, however, is in direct contrast with the observation made by photoemission experiments of a significant (~50 meV) gap in density-ofstates at the Fermi level at the antinodes [14][15][16] .…”

“…Complementary photoemission experiments at zero field [14][15][16] , optical conductivity experiments up to 8 T, and high field heat capacity 27 experiments indicate a concentration of density-ofstates at the Fermi level solely at the nodal location in momentum space. Taken together with the persistence of quantum oscillations unaltered in form down to low fields ~22 T where the d-wave superconducting gap is well developed, the quasi-two-dimensional Fermi surface pocket that gives rise to multiple frequency components observed by quantum oscillations in underdoped YBa 2 Cu 3 O 6 + x is likely connected with the nodal region of the Brillouin zone.…”

“…Also consistent with this expectation is the observed absence of a low-angle spin zero as discussed earlier for the second , represented by solid dots. The ratio of the amplitude of the harmonic (solid lines) to the square of the fundamental (shown by dots and the envelope shown by green shading-extracted from the square of the fundamental oscillations maxima and minima) yields a value of 2Γ 38° = 1.0(3) from equation (2), from which we obtain Γ 38° = 0.50 (15). (c) Dingle analysis, performed on a linear-log plot of the fundamental oscillations in contactless resistivity (denoted by solid circles, determined from the oscillation maxima and minima after dividing out R T,1 ) at θ = 38° up to fields of 85 T, plotted versus 1/B.…”

“…The Fermi surface pocket responsible for quantum oscillations is likely located at the nodal region, given that these oscillations persist down to low magnetic fields, where the d-wave superconducting gap is well developed, whereas complementary experiments up to these fields [14][15][16]27 find a concentration in the density-of-states at the Fermi level at the nodes of the superconducting wavefunction. Translational symmetry-breaking models proposed thus far are either nodal-antinodal (for example, refs 11,12), which would be inconsistent with the current experimental results, or comprise solely nodal hole pockets 13 , which would be difficult to reconcile with negative Hall and Seebeck effect 4,20 , leaving us with a dilemma.…”

“…The next question relates to the location of this quasi-two-dimensional pocket. We consider complementary experiments: photoemission experiments at zero field [14][15][16] , optical conductivity experiments up to 8 T (refs 25,26), and high field heat capacity experiments (ref. 27) indicate a solely nodal concentration of the density-ofstates at the Fermi level.…”