Spin dynamics in the low-temperature tetragonal phase of ≃1/8 doped single crystal La1.67Eu0.2Sr0.13CuO4

We present La-139 and Cu-63 NMR relaxation measurements in single crystal La1.67Eu0.2Sr0.13CuO4. A strong peak in the La-139 spin-lattice relaxation rate observed in the spin ordered state is well described by the BPP mechanism [Bloembergen, Purcell, and Pound, Phys. Rev. 73, 679 (1948)] and arises from continuous slowing of electronic spin fluctuations with decreasing temperature; these spin fluctuations exhibit XY-like anisotropy in the ordered state. The spin pseudogap is significantly enhanced by the static charge-stripe order in the LTT phase.