Effect of magnetic impurities on spin fluctuations in La 2− xSr xCuO 4

Abstract

Neutron scattering experiments for La 1.85Sr 0.15Cu 0.98Ni 0.02O 4 ( T c=28 K) demonstrated that well-defined incommensurate peaks appear in the superconducting state, giving an enhancement of χ ″( q IC, ω) at ∼1 meV associated with a sharpening of peak width. Thus, the Ni impurities induce low-energy excitations and smear the sharp edge structure in χ ″( q IC, ω) reported from the Ni-free system. On the other hand, no clear signature of magnetic ordering was observed in the elastic channel even at the lowest temperature. We conjecture that spin fluctuations around Ni impurities never quench but gradually slow down over a wide space, in contrast to Zn doping which locally destroys superconductivity in a drastic manner.