Abstract
We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic t-J Heisenberg model on the honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures and hole dopings, the electronic spectrum of excitations, the spin-excitation spectrum and thermodynamic quantities (two-spin correlation functions, staggered magnetization, magnetic susceptibility, correlation length) are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature and doping dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. Our results on the doping dependencies of the magnetization and susceptibility are analyzed in comparison with previous results for the t-J model on the square lattice.
Highlights
In recent years the two-dimensional carbon honeycomb lattice, the graphene, has been extensively studied due to its peculiar electronic properties
We study the Hubbard model on the honeycomb lattice in the limit of strong electron correlations U >> t, when it can be reduced to the one-subband t-J model: H = −t a+i,σaj,σ − μ ni,σ + HH, (1)
To evaluate the spin-excitation spectrum and the thermodynamic properties, the correlation functions C1, C2, the transfer amplitudes D1, D2, and the vertex parameters α1, α2, and λ, appearing in the spectrum ω±(q) as well as the condensation term C in the long-range order (LRO) phase have to be determined as solution of a coupled system of selfconsistency equations
Summary
In recent years the two-dimensional carbon honeycomb lattice, the graphene, has been extensively studied due to its peculiar electronic properties (for a review see [1,2]). The transition from the weak-coupling semimetal to the strong-coupling insulating phase was studied in [15] using QMC simulations for the SU(N )symmetric Heisenberg model with the nn flavor exchange interaction on the honeycomb lattice at half filling. The existence of the spin-liquid state in the Hubbard model on the honeycomb lattice is still under discussion, the transition from the semimetal to the AF LRO phase is proved for a large enough single-site CI, U > Uc ≈ 4t. Superconducting phase transitions in the Hubbard model on the honeycomb lattice have been considered in several publications. Less attention has been paid to the investigation of electron- and spin-excitation spectra and of thermodynamic properties as functions of temperature and electron concentration Motivated by this shortcoming, in the present paper we report results of investigations of these spectra and of the thermodynamics in the limit of strong correlations within the t-J model.
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