Bogoliubov angle in electron-doped cuprate superconductors

Within the framework of the kinetic energy driven superconducting mechanism, the momentum dependence of the Bogoliubov angle in the electron-doped cuprate superconductors is studied. By calculation of the ratio of the low energy quasiparticle spectra at positive and negative energies, it is shown that the Bogoliubov angle increases monotonically across the Fermi crossing point, suggesting a continuously evolution of the particle and hole mixing. The electron-doped cuprate superconductors are an important component in the puzzle of the high temperature superconductivity. The undoped material is a Mott insulator with the antiferromagnetic long-range order, then superconductivity emerges when electrons are doped into this Mott insulator [1]. It has been found that only an approximate symmetry in the phase diagram exists about the zero doping line between the hole-doped and electron-doped cuprates, and the significantly different behavior of the electron-doped and hole-doped cuprates is observed, reflecting the electron-hole asymmetry [1]. Furthermore, in spite of the unconventional superconducting (SC) mechanism, the angle-resolved photoemission spectroscopy experimental results have unambiguously established the Bogoliubov quasiparticle nature of the sharp SC quasiparticle peak in the hole-doped cuprate superconductors [2, 3], then the SC coherence of the low energy quasiparticle peak is well described by a simple d-wave BCS formalism [4]. In this case, the investigation of the similarities and differences of the Bogoliubov quasiparticle nature between the hole-doped and electron-doped cuprate superconductors would be crucial to understand the SC mechanism of cuprate superconductors. The Bogoliubov quasiparticle is a coherent combination of particle (electron) and its absence (hole), i.e., its annihilation operator is a linear combination of particle and hole operators as [5] γk↑ = Ukck↑ + Vkc † −k↓, with the constraint for the coherence factors |Uk| 2 + |Vk| 2 = 1 for any wave vector k (normalization). In this case, the Bogoliubov quasiparticle do not carry definite charge. This particle-hole dualism of Bogoliubov quasiparticles then is responsible for a variety of profound phenomena in the SC state. Recently a quantity referred to as the Bogoliubov angle has been introduced in terms of the coherence factors Uk and Vk as [6],