Theory of spin dynamics in electron-doped high-Tc superconductors

Abstract

Spin dynamics in the superconducting and the normal state of electron-doped high-Tc cuprates is studied based on the scenario of the Fermi surface topology. We use the slave-boson mean-field approach to the t−t′−J model and include the antiferromagnetic spin fluctuations via the random-phase approximation. A detailed analysis of the momentum and energy dependences of the dynamical spin susceptibility for different dopings is performed. It is found that the spin response in the superconducting state is commensurate in the overdoped regime and above a frequency typically of 0.07J in the underdoped and optimally doped regime. Meanwhile, it is commensurate in the normal state. These are consistent with the recent neutron-scattering experiment. The low-energy incommensurate response shows weak frequency dependence and its incommensurability is very small. These results contrast with those in the hole-doped cuprates in which the spin response is incommensurate except when it is at the resonance frequency and shows a remarkable downward dispersion. A strong frequency dependent change in spin response when entering the superconducting state is found. The frequency dependence of the spin response shows that a spin resonance appears in the underdoped regime, but does not in the overdoped regime.

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