Dynamic spin susceptibility in thet−Jmodel

Abstract

A relaxation-function theory for the dynamic spin susceptibility in the t-J model is presented. By a sum-rule-conserving generalized mean-field approximation (GMFA), the two-spin correlation functions of arbitrary range, the staggered magnetization, the uniform static susceptibility, and the antiferromagnetic correlation length are calculated in a wide region of hole doping and temperaturs. A good agreement with available exact diagonalization (ED) data is found. The correlation length is in reasonable agreement with neutron-scattering experiments on La 2−δ Sr δ CuO4. Going beyond the GMFA, the self-energy is calculated in the mode-coupling approximation. The spin dynamics at arbitrary frequencies and wave vectors is studied for various temperatures and hole doping. At low doping a spin-wave-type behavior is found as in the Heisenberg model, while at higher doping a strong damping caused by hole hopping occurs, and a relaxation-type spin dynamics is observed in agreement with the ED results. The local spin susceptibility and its ω/T scaling behavior are calculated in a reasonable agreement with experimental and ED data.

On the theory of superconductivity in the extended Hubbard model

“…This type of the spin-excitation spectrum was found also in the microscopic theory for the t-J model in Ref. [44]. The strength of the spinfluctuation interaction given by the static susceptibility χ Q = χ sf (Q) at the AF wave vector Q = (π, π), is fixed by the normalization condition:…”

“…By taking into account contributions from the CI and the EPI in Eq. (7) and using the NCA in calculation of the respective time-dependent correlation functions we obtain the kernel (44) for the integral equations (42) and (43).…”

Kinematic spin-fluctuation mechanism of high-temperature superconductivity

“…It is assumed that the system is far away from a charge instability or a stripe formation and charge-fluctuations give a small contribution to the pairing. The largest contribution from spin fluctuations comes from wave-vectors close the AF wave-vector Q = (π, π) where their energy ω s (Q) is much smaller than the Fermi energy, ω s (Q)/µ ≪ 1 (see, e.g., [26]). Therefore, vertex corrections to the kinematic interaction should be small as in Eliashberg theory [24] for electron interaction with phonons, where ω ph (q)/µ ≪ 1 .…”

Фрустрированный $J_{1}$-$J_{2}$-$J_{3}$ Квантовый Двумерный Антиферромагнетик В Сферически-Симметричном Самосогласованном Подходе

“…Обсудим значения параметра затухания γ в (15), принимаемые как в преды-дущих рассмотрениях, так и в настоящей работе. Некоторые указания на поря-док величины γ во фрустрированной спиновой модели можно получить, анали-зируя доступные результаты для t-J модели [22], [30]. При этом предполагает-ся, что качественно увеличение допирования в модели с носителями соответствует увеличению фрустрации в чисто спиновой модели.…”

“…Если рассматривать систему в спин-жидкостном состоянии, то следует сравнивать затухание с данными t-J моде-ли при таком допировании, когда LRO отсутствует. В работе [30] соответствующее допирование δ = 0.15 приводит к минимальному значению γ ∼ 0.7J, близкому к значениям, принимаемым нами ниже. Отметим, что к значениям γ > 0.7J приво-дит экстраполяция к нулю температурной зависимости γ(T ) из данных кластер-ной диагонализации [22].…”