SPIN DYNAMICS STUDY OF LA2-XSRXCUO4 BY INELASTIC NEUTRON-SCATTERING

We present inelastic neutron scattering measurements performed on thre e La2-xSrxCuO4 high T-c single crystals, with x = 10%, 15% and 20% (T- c= 25, 35 and 12K, respectively). We report here a complete study of t he evolution of delta with doping providing evidence far a saturation of delta in the overdoped regime. In addition, for x = 10%, while the low energy magnetic fluctuations are clearly peaked at incommensurate positions, the high energy response evolves back to the commensurate p osition (pi,pi) and drops to the background above around 60 meV. Below T-c, a 3.5 meV magnetic gap opens up for the optimaI doping is (x=15% ), while for the underdoped and overdoped crystals is (x=10% and 20%) our experiment fails to reveal any significant magnetic gap above 1.2 meV and down to 1.5 K.