Study of the vortex dynamics in single crystals of the high-T c superconductor Tl2Ba2CaCu2O8 via205Tl NMR

The²⁰⁵Tl linewidth in single crystals of the high-T _c superconductor Tl₂Ba₂CaCu₂O₈ (T _c≈105 K) is analyzed for the normal (N) and impurity (I) Tl-sites. On the I-sites Ca has been replaced by Tl. Measurements were performed in a field of 4.7 T. The normal state linewidth on the N and I sites is shown to be mainly determined by a distribution in Knight shifts. To simulate the final increase below 50 K we have studied the vortex lattice in a single superconducting sheet by a molecular dynamics method for systems up to 2000 vortices. The results compare well with the experimental data. This implies that the temperature dependence of the linewidth in this highly anisotropic material is determined by flux dynamics and only marginally by the temperature dependence of the penetration depth.