Dispersion of Nd spin correlations in heavy-fermion like Nd1.85Ce0.15CuO4

The T'-phase compound Nd2-xCexCuO4 exhibits at T < 2 K resemblance with hea vy-fermion behavior above a critical Ce content which has been established by specific heat, magnetic susceptibility, magnetoresistance, and mu SR exp eriments and described qualitatively by the Zeeman route to heavy-fermion b ehavior. We present inelastic neutron scattering measurements at the onset of this doping regime at x = 0.15 performed on a single crystal at T = 0.05 K. The magnetic response from correlated Nd spins is reminiscent of the sp in waves in Nd2CuO4. The dispersion of the Nd-Nd correlations has been dete rmined in several Brillouin zones along the line Gamma MAZ Gamma. Its mediu m energy is shifted to lower energies by more than 40% compared to the undo ped compound. An energy gap of the Nd-Nd correlations is still observed but also an incipient soft mode has been found between the points A and M, whi ch might indicate a magnetic instability. In addition, single-site scatteri ng from slowly relaxing Nd spins contributes to the total magnetic scatteri ng, indicating a hybridization of the Nd-4f electrons with the strongly cor related Cu-3d conduction electrons. (C) 1999 American Institute of Physics. [S0021-8979(99)24908-0].