SPIRAL PHASE OF A DOPED ANTIFERROMAGNET

The stability of the spiral phase is studied in the t-J model for low doping concentrations. A Green's-function formalism is used that is based on a slave-fermion Schwinger-boson representation in a twisted local coordinate frame. The spiral modulation, which is treated within the self-consistent Born approximation, gives rise to a splitting of the band of quasiholes, leading to a stable spiral phase. The wave number of the spiral phase is calculated, and shown to increase with decreasing ratio J/t. We also study the effects of the spiral modulation on spin waves. Spin waves with momenta parallel to the modulation vector couple strongly to electron-hole pairs that have an excitation gap. The resulting hybridized modes are specified, and the strong renormalization of the spin-wave velocity is pointed out.