Two-dimensional t-J model at moderate doping

Abstract

Using the method which retains the rotation symmetry of spin components in the paramagnetic state and has no preset magnetic ordering, spectral and magnetic properties of the two-dimensional t-J model in the normal state are investigated for the ranges of hole concentrations 0 ≤ x ≤ 0.16 and temperatures 0.01t ≤ T ≤ 0.2t. The used hopping t and exchange J parameters of the model correspond to hole-doped cuprates. The obtained solutions are homogeneous which indicates that stripes and other types of phase separation are not connected with the strong electron correlations described by the model. A series of nearly equidistant maxima in the hole spectral function calculated for low T and x is connected with hole vibrations in the region of the perturbed short-range antiferromagnetic order. The hole spectrum has a pseudogap in the vicinity of (0, π) and (π, 0). For x ≈ 0.05 the shape of the hole Fermi surface is transformed from four small ellipses around (±π/2, ±π/2) to two large rhombuses centered at (0, 0) and (π, π). The calculated temperature and concentration dependencies of the spin correlation length and the magnetic susceptibility are close to those observed in cuprate perovskites. These results offer explanations for the observed scaling of the static uniform susceptibility and for the changes in the spin-lattice relaxation and spin-echo decay rates in terms of the temperature and doping variations in the spin excitation spectrum of the model. PACS. 71.10.Fd Lattice fermion models -74.25.Ha Magnetic properties -74.25.Jb Electronic structure

Dynamic spin susceptibility in thet−Jmodel

“…The increase of ω m with δ at low T is in qualitative agreement with the findings of Ref. [18] (T = 0.02t) and with experiments.…”

“…10 (c), with increasing δ the maximum in χ ′′ (q, ω) with q = (π, 0) is shifted to lower frequencies, in qualitative agreement with the theory of Ref. [18].…”

“…[18]- [20] and [22] and describes the damping due to the decay of spin fluctuations into electron-hole excitations. The same result can be deduced, if in the mode-coupling approximation (see Appendix, Eq.…”

“…[18] - [21], we have taken into account all contributions to the spin-excitation spectrum ω q in the GMFA and to the self-energy Σ(q, ω) and thoroughly analyzed their temperature and doping dependence. In particular, we have found that the contribution from the hole-hopping term ∝ t 2 in the spectrum ω q , Eq.…”

“…[16] A similar approach based on the Mori projection technique for the singleparticle electron GF and spin GF has been used in Refs. [18,19,20,21]. The magnetic resonance mode observed in the superconducting state was studied within the memory-function approach in Refs.…”