Since their discovery in 1986 high-temperature superconductors (HTSC) are considered
interesting physical systems as well as attractive candidates for a variety of technical
applications. In both cases one of the key aspects to be understood is the mechanism of power
dissipation which depends primarily on vortex dynamics: the movement of magnetic flux lines in
the superconductor when a transport current is applied.The present work studies vortex dynamics
in experiments on two of the most prominent types of HTSC materials YBa2Cu3O7 (YBCO) and
Bi2Sr2CaCu2O8+d (BSCCO) in the limit of low and high current densities. Both the applied
transport current density and the dimensionality of the materials strongly influence the
dynamic response.For the low current limit in BSCCO this thesis concentrates on the influence
of oxygen stoichiometry and in YBCO on a vortex glass phase which indicates a true
superconducting state with vanishing linear resistivity. In the high current limit for the
first time a vortex instability is shown to exist in BSCCO apparently arising from a fluid
phase while a similar phenomenon in YBCO reveals a clear correlation of the high-dissipative
instability to the low-dissipative vortex glass phase.
