Comparative Study of Vortex Correlation in Twinned and Untwinned YBa2Cu3O7 Single Crystals

F. DE LA CRUZ; D. LOPEZ; E. F. RIGHI; G. NIEVA

Conferencia; 10th Anniversary HTS Workshop; 1996

Vortex correlation in the c crystallographic direction in YBCO single crystals has been studied by means of transport measurements. The solid-liquid phase transition in untwinned single crystals is followed by a discontinuous change from a vortex structure that is correlated in the c direction to a non correlated liquid in all directions. Correlated vortex liquids in the c direction are only possible when extended defects such as twin boundaries stabilize a finite temperature dependent vortex correlation in the field direction. In this case the liquid can be characterized by vortex lines with a diverging temperature dependent length.