Electronic Spectra and Their Relation to the(π,π)Collective Mode in High-TcSuperconductors

Abstract

Photoemission spectra of Bi2Sr2CaCu2O 8+δ reveal that the high energy feature near (π, 0), the "hump", scales with the superconducting gap and persists above Tc in the pseudogap phase. As the doping decreases, the dispersion of the hump increasingly reflects the wavevector (π, π) characteristic of the undoped insulator, despite the presence of a large Fermi surface. This can be understood from the interaction of the electrons with a collective mode, supported by our observation that the doping dependence of the resonance observed by neutron scattering is the same as that inferred from our data.

Electronic structure of cuprate superconductors in a full charge-spin recombination scheme

“…However, one of the most striking dilemmas is that the SC coherence of the low-energy quasiparticle excitations in cuprate superconductors seems to be described by the standard Bardeen-Cooper-Schrieffer (BCS) formalism [15][16][17][18][19] , although the normal-state is undoubtedly not the standard Landau Fermi-liquid on which the conventional electron-phonon theory is based. Angle-resolved photoemission spectroscopy (ARPES) experiments reveal sharp spectral peaks in the singleparticle excitation spectrum 5,6,[15][16][17][18][19][20][21][22][23] , indicating the presence of quasiparticle-like states, which is also consistent with the long lifetime of the electronic state as it has been determined by the conductivity measurements 10,11 . In particular, as a direct method for probing the electron Fermi surface, the early ARPES measurements indicate that in the entire doping range, the underlying electron Fermi surface satisfies Luttinger's theorem [24][25][26][27] , i.e., the electron Fermi surface with the area is proportional to 1 − δ.…”

“…3, the thick solid curve is the momentum distribution curve where the electron coherence factors U 2 k = V 2 k at the electron Fermi energy. It is apparent that the theoretical result captures the qualitative feature of the momentum dependence of the electron spectrum observed experimentally on cuprate superconductors in the SC-state 5,6,[15][16][17][18][19][20][21][22][23] . There are two branches of dispersion centered at the electron Fermi energy, however, two sharp low-energy SC quasiparticle peaks in each energy distribution curve exhibit an evolution of the relative peak height at different momentum positions due to the momentum dependence of the coherence factors.…”

“…Later, the ARPES experimental studies show that in the underdoped and optimally doped regimes, although the antinodal region of the electron Fermi surface is gapped out, leading to the notion that only part of the electron Fermi surface survives as the disconnected Fermi arcs around the nodes [28][29][30][31][32] , the underlying electron Fermi surface determined from the low-energy spectral weight still fulfills Luttinger's theorem in the entire doping range 32 . These ARPES experimental facts [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] on the other hand provide strong evidences supporting the notion of the charge-spin recombination 13,14 . Since the electron Fermi surface is a fundamental property of interacting electron systems, the study of the nature of the electron Fermi surface should be crucial for understanding the electronic structure of cuprate superconductors.…”

“…(15) and (16), the electron Fermi surface in the entire doping range forms a continuous contour in momentum space [24][25][26][27] . Moreover, according to one of the self-consistent equations (20), the electron Fermi surface satisfies Luttinger's theorem, i.e., the electron Fermi surface area contains 1 − δ electrons. However, we will show in the following discussions that in the underdoped and overdoped regimes, the energy and momentum dependence of the electron self-energy in the particle-hole channel truncates this continuous contour in momentum space into the disconnected Fermi arcs located around the nodal region of BZ.…”

The resonant magnetic mode: A common feature of high-Tc superconductors

“…Besides the observation of the magnetic resonance peak below Tc by INS, anomalies in the quasiparticle spectra has been also reported by photoemission [16], optical conductivity [17], tunneling [18], and Raman scattering techniques. Their interpretation as an evidence of the coupling of quasiparticules to the neutron mode has stimulated spin fluctuation based pairing scenarios which are, however, still controversial [2].…”