Spin dynamics study of La2-xSrxCuO4 by inelastic neutron scattering

We present inelastic neutron scattering measurements performed on three 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 the 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 position (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.