Abstract
The electron paramegnetic resonance (EPR) of Mn 2+ doped into La 2-x Sr x CuO 4 was used to probe the copper spin relaxation via the bottleneck effect for oxygen isotope ( 16 O and 18 O)-substituted samples. It was found that the EPR linewidth is larger for the 18 O isotope samples than for the 16 O samples. For x = 0.03, the linewidth for the 18 O sample is larger than for 16 O sample by a factor of 2. The isotope effect is pronounced at low temperatures and decreases with increasing Sr concentration. This effect is quantitatively explained by the Cu 2+ S = 1/2 spin relaxation to the lattice via Dzyaloshinski terms coupled linearly to the local Q 4 /Q 5 tilting modes of the CuO 6 octahedra as proposed by Kochelaev et al. [1] 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 (HTSC).
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