Asymmetry of the electron spectrum in hole-doped and electron-doped cuprates

Abstract

Within the t-t ′ -J model, the asymmetry of the electron spectrum and quasiparticle dispersion in hole-doped and electron-doped cuprates is discussed. It is shown that the quasiparticle dispersions of both hole-doped and electron-doped cuprates exhibit the flat band around the (π, 0) point below the Fermi energy. The lowest energy states are located at the (π/2, π/2) point for the hole doping, while they appear at the (π, 0) point in the electron-doped case due to the electron-hole asymmetry. Our results also show that the unusual behavior of the electron spectrum and quasiparticle dispersion is intriguingly related to the strong coupling between the electron quasiparticles and collective magnetic excitations. 74.25.Jb, 74.62.Dh, The parent compounds of cuprate superconductors are believed to belong to a class of materials known as Mott insulators with an antiferromagnetic (AF) longrange order (AFLRO), then superconductivity emerges when charge carriers, holes or electrons, are doped into these Mott insulators 1-3 . Although both hole-doped and electron-doped cuprates have the layered structure of the square lattice of the CuO 2 plane separated by insulating layers 1-3 , the significantly difference of the electronic states between hole-doped and electron-doped cuprates is observed 4,5 , which reflects the electron-hole asymmetry. For the hole-doped cuprates, AFLRO is reduced dramatically with doping 1,6 , and vanished around the doping δ ∼ 0.05. But a series of inelastic neutron scattering measurements show that the incommensurate short AF correlation persists in the underdoped, optimally doped, and overdoped regimes 1,6 , then in low temperatures, the systems become superconducting (SC) over a wide range of the hole doping concentration δ, around the optimal doping δ ∼ 0.15 2,7 . However, AFLRO survives until superconductivity appears over a narrow range of δ, around the optimal doping δ ∼ 0.15 in the electrondoped cuprates 3,8,9 . In particular, the maximum achievable SC transition temperature in the electron-doped cuprates is much lower than that in the hole-doped case, and the commensurate spin response in the SC-state is observed 10 . These experimental observations show that the unconventional physical properties of both holedoped and electron-doped cuprates mainly depend on the extent of the doping concentration. Since many of the unconventional physical properties, including the relatively high SC transition temperature, have often been attributed to particular characteristics of low energy excitations determined by the electronic structure 1,4 , then a central issue to clarify the nature of the unconventional physical properties is how the electronic structure evolves with the doping concentration, From the angle-resolved photoemission spectroscopy (ARPES) measurements 4,11 , it has been shown that the electron spectral function A(k, ω) in doped cuprates is strongly momentum and doping dependent. For the hole doping, the charge carriers doped into the parent Mott insulators first enter into the k = [π/...

Electronic Structure of Kinetic Energy Driven Cuprate Superconductors

“…In particular, we show that one of the universal features is that the d-wave superconducting state in cuprate superconductors is the conventional BCS like, so that the basic BCS formalism with the d-wave symmetry is still valid in discussions of the low energy electronic structure of cuprate superconductors [32,33,35,37], although the pairing mechanism is driven by the kinetic energy by exchanging spin excitations, and other exotic magnetic properties [16,17,18] are beyond the BCS formalism. Our these theoretical results [32,33,34,35,36,37] also show that the striking behavior of the electronic structure in cuprate superconductors is intriguingly related to the strong coupling between the electron quasiparticles and collective magnetic excitations. This paper is organized as follows.…”

“…In this paper, we give a brief review of our recent studies for the low energy electronic structure of the kinetic energy driven d-wave cuprate superconductors [32,33,34,35,36,37]. We show that in both superconducting and normal states, the spectral weight increases with increasing doping, and decreases with increasing temperatures [32,33,34,35,36,37]. Furthermore, the superconducting quasiparticles around the [π, 0] point disperse very weakly with momentum [35,37].…”

“…It has been shown [49] that this defect can be cured by introducing a projection operator P i , i.e., the electron operator C iσ with the single occupancy local constraint (2) can be mapped exactly using the charge-spin separation fermion-spin transformation (9) defined with an additional projection operator P i . However, this projection operator is cumbersome to handle in the many cases, and it has been dropped in the actual calculations [29,30,31,32,34,35,36,37,33,49]. It has been shown [29,49,52] that such treatment leads to errors of the order δ in counting the number of spin states, which is negligible for small doping.…”

“…Within this framework of the kinetic energy driven superconductivity, we [32,33,34,35,36,37] have performed a systematic calculation for the low energy electron spectral function of the single layer and bilayer cuprate superconductors in both superconducting and normal states, and qualitatively reproduced all main features of the ARPES experimental measurements on the single layer and bilayer cuprate superconductors [4,5]. In this paper, we give a brief review of our recent studies for the low energy electronic structure of the kinetic energy driven d-wave cuprate superconductors [32,33,34,35,36,37]. We show that in both superconducting and normal states, the spectral weight increases with increasing doping, and decreases with increasing temperatures [32,33,34,35,36,37].…”

“…It is shown that the charge-spin separation fermion-spin representation is a natural representation of the constrained electron defined in a restricted Hilbert space without double electron occupancy. Within this charge-spin separation fermion-spin theory [29] and kinetic energy driven superconducting mechanism [30,31], the electronic structure of the single layer cuprate superconductors in both superconducting and normal states [32,33,34,35] is presented in section 3. It is shown that the superconducting coherence of the quasiparticle peak is described by the simple BCS formalism.…”