DOPING AND TEMPERATURE DEPENDENCE OF INCOMMENSURAT E ANTIFERROMAGNE TISM IN UNDERDOPED LANTHANUM CUPRATES

The doping, temperature, and energy dependence of the dynamical spin structure factors of the underdoped lanthanum cuprates in the normal state are studied within the t-J model using the fermion-spin transformation technique. Incommensurate peaks are found at [(1 +/- delta) pi, pi], [pi, (1 +/- delta) pi] at relatively low temperatures, with delta linearly increasing with doping at the beginning and then saturating at higher dopings, These peaks broaden and weaken in amplitude with temperature and energy, in good agreement with experiments. The theory also predicts a rotation of these peaks by pi /4 at even higher temperatures, being shifted to [(1 +/- delta/ root2)pi, (1 +/- delta/ root2)delta].