Tilting mode relaxation and oxygen isotope effect in La2-xSrxCuO4 studied by electron paramagnetic resonance

The electron paramegnetic resonance (EPR) of Mn2+ doped into La2-xSrxCuO4 w as used to probe the copper spin relaxation via the bottleneck effect for o xygen isotope (O-16 and O-18)-substituted samples. It was found that the EP R linewidth is larger for the O-18 isotope samples than for the O-16 sample s. For x = 0.03, the linewidth for the O-18 sample is larger than for O-16 Sample by a factor of 2. The isotope effect is pronounced at low temperatur es and decreases with increasing Sr concentration. This effect is quantitat ively explained by the Cu2+ S = 1/2 spin relaxation to the lattice via Dzya loshinski terms coupled linearly to the local Q(4)/Q(5) tilting modes of th e CuO6 octahedra as proposed by Kochelaev et al. [1] The (Q(4)/Q(5) modes a re coupled sterically to the Q(2) Jahn-Teller modes considered to be releva nt for the (bi)-polaron formation and thus for the high-temperature superco nductivity (HTSC).