Spin polaron in the J1-J2 Heisenberg model

We have studied the validity of the spin-polaron picture in the frustrated J(1)-J(2) Heisenberg model. For this purpose, we have computed the hole spectral functions for the Neel, collinear, and disordered phases of this model by means of the self-consistent Born approximation and Lanczos exact diagonalization on finite-size clusters. We have found that the spin-polaron quasiparticle excitation is always well defined for the magnetically ordered Neel and collinear phases, even in the vicinity of the magnetic quantum critical points, where the local magnetization vanishes. As a general feature, the effect of frustration is to increase the amplitude of the multimagnon states that build up the spin-polaron wave function, leading to the reduction of the quasiparticle coherence. Based on Lanczos results, we discuss the validity of the spin-polaron picture in the disordered phase.