engleski

The axial oxygen and structural anomalies in high-T_c materials

Using copper K-edge X-ray-absorption Fine Structure (XAFS) a two-site distribution for the Cu-axial oxygen has been found in YBa_2Cu_3O_7, YBa_2Cu_3O_6.5, and TlBa_2Ca_3Cu_4O_11. This distribution is modelled by a double-well potential, with dynamical tunnelling between the two sites, which changes in proximity to T_c. XAFS also shows the presence of a similar double-well in YBa_2Cu_3O_6.5 and its disappearance in YBa_2Cu_2.8Co_0.2O_7, indicating a correlation between this local distortion and T_c. Unpolarised XAFS studies in TlBa_2Ca_3Cu_4O_11 indicate that the separation between the two positions is larger than in YBa_2Cu_3O_7. The sensitivity of XAFS to these local lattice anomalies vis-a-vis diffraction is discussed.

high temperature superconductor; structural anomalies; K-edge; X-ray-absorption Fine Structure

nije evidentirano