Tilting mode relaxation in the electron paramagnetic resonance of oxygen-isotope-subsbituted La2-xSrxCuO4:Mn2+ -: art. no. 144513

The electron paramagnetic resonance (EPR) of Mn2+ doped into La2-xSrxCuO4 was used to probe the copper spin relaxation via the bottleneck effect for oxygen isotope (O-16 and O-18) substituted samples. The concentration range a extended from 0.06 to 0.20 and the temperature dependence of the EPR linewidth was studied from 4 to 300 K. It was found that the EPR linewidth is larger for the O-18 isotope samples than for the O-16 samples. The isotope effect is pronounced at low temperatures and decreases with increasing Sr concentration. This effect is quantitatively explained by the Cu2+ S=1/2 spin relaxation to the lattice via Dzyaloshinski terms coupled linearly to the local Q(4)/Q(5) tilting modes of the CuO6 octahedra as proposed by B. I. Kochelaev [J. Supercond. 12, 53 (1999)]. The Q(4)/Q(5) modes are coupled sterically to the Q(2) Jahn-Teller modes considered to be relevant for the (bi)polaron formation and thus for the high-temperature superconductivity.