Antiferromagnetic ordering and disappearance of pseudogap within the vortex core of Tl₂Ba₂CuO₆₊δ

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Spatially-resolved NMR is used to probe the magnetism in and around the vortex core of nearly optimally-doped Tl₂Ba₂CuO₆₊δ (Tc=85K). The NMR relaxation rate T₁⁻¹ at ²⁰⁵Tl site, at which antiferromagnetic (AF) fluctuation can be monitored sensitively, provides a direct evidence that the AF spin correlation is significantly enhanced in the vortex core region. In the core region Cu spins show a local AF ordering with moment 0.1μB parallel to the layers at Tₙ=20K. Above Tₙ the core region is in the paramagnetic state which is a reminiscence of the state above the pseudogap temperature (T*=120K), indicating that the pseudogap disappears within the core.