Spin and charge fluctuations in the phase-modulated antiferromagnetic state of a t- t′- J model

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The T = 0 phase diagram of a t- t′- J model on a square lattice, where t′ denotes hopping along the diagonal, has been recently determined within a suitable 1/ N expansion. Close to half-filling and for sufficiently large t′, an unconventional antiferromagnetic (AF) state, characterized by the usual (π, π), i.e., Néel, modulation of the spin configuration and an unusual (π, −π) phase modulation, is stabilized. A characteristic feature of this novel AF state is an anisotropy in the velocities of its elementary excitations which is suppressed, however, at half-filling. The spin-spin dynamical structure factor exhibits a double peak at finite doping, which reflects hybridization between the relevant transverse (magnonlike) and longitudinal (holonlike) modes, one of the peaks also being suppressed at half-filling. The real part of the finite-frequency conductivity displays a structureless broadband regime at low frequencies, in qualitative agreement with infrared absorption experiments in doped antiferromagnets.