Momentum dependent relaxation rate and pseudogap in doped magnetic insulators

The spectral functions and corresponding self energies are calculated within the planar t-t'-J model as relevant to hole-doped cuprates using the exact diagonalization method at finite temperatures, combined with the averaging over twisted boundary conditions. Results show truncated Fermi surface at low doping and t'<0 in the antinodal region while the self energy reveals weakly k- and doping dependent anomalous relaxation rate |\Sigma''(k,\omega)|~ a+b|\omega| for \omega<0, consistent with recent ARPES results, and a pseudogap-generating component of Lorentzian form. The latter is well pronounced at low doping and strongly depends on k and t'.