Inhaltszusammenfassung

Epitaxial YBa2CU3OT-thin films with the c-axis oriented perpendicular to the film plane were prepared by dc-sputtering from a single stoichiometric target on (100) SrTiO 3- substrates. Typical values of the inductively measured superconducting transitions were about 90 K with a width less than 0.5 K. Critical current densities were measured on 5 to 10 gm wide strips as function of magnetic field and temperature. The temperature dependences of Jc follow a universal function Jc (B, T) =j* (T= 0...Epitaxial YBa2CU3OT-thin films with the c-axis oriented perpendicular to the film plane were prepared by dc-sputtering from a single stoichiometric target on (100) SrTiO 3- substrates. Typical values of the inductively measured superconducting transitions were about 90 K with a width less than 0.5 K. Critical current densities were measured on 5 to 10 gm wide strips as function of magnetic field and temperature. The temperature dependences of Jc follow a universal function Jc (B, T) =j* (T= 0, B) *9( 1-T/T~(B) ) ~ with ~- 1 . 5 _ 0 . 1 . For B=0 and T=77 K we obtained j~=4-106A/cm 2. The field dependence of the resistive transitions was measured with the magnetic field parallel to the c-axis. The slope of the upper critical field Bc2(T) was determined for different criteria. The carrier concentration evaluated from Halleffect measurements was found to decrease linearly from one per unit cell at 240 K with decreasing temperature extrapolating nearly through zero for T= 0. Highly resolved angular dependent measurements of the critical current density with B perpendicular to the current but tilted from the c-axis show a very strong and sharp enhancement of jc for the magnetic field parallel to the (CuO2)-layers (B_L c). Additionally to this phenomenon, which is caused by an intrinsic pinning mechanism due to the layered structure of high-To-superconductors the influence of the anisotropy of the upper critical field on j~(B, T, ~o) is evident near T~.» weiterlesen» einklappen

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Klassifikation

DFG Fachgebiet:
Physik der kondensierten Materie

DDC Sachgruppe:
Physik