摘要:

Critical currents of YBaCuO ceramics were measured at 77 K by transport measurements in an applied magnetic fieldH. A hysteretic behavior between 10 and 10 000 G was observed. For decreasing fields, the critical currentJcobeys a power lawH−nwithnranging between 0.6 and 2.8. The exponentnis correlated with the microstructure and the average grain size of the ceramic. This power law behavior is discussed in terms of modified flux creep and flux flow regimes related to the microstructure.

ISSN:0003-6951    

DOI:10.1063/1.102537

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Significantly improved flux pinning has been achieved in bulk YBa2Cu3O7−&dgr;superconductor (‘‘123’’ compound) containing fine‐scale defects (<∼50 A˚ thick). The measuredJcintragrain of ∼105A/cm2at 77 K,H=0.9 T is about ten times higher than the typical values for bulk Y‐Ba‐Cu‐O. The improved structure was produced by rapid decomposition at 920 °C of the YBa2Cu4O8(‘‘124’’) precursor. This new and simple processing route could lead to a commercially viable processing technique for flux‐pinning enhancement in bulk Y‐Ba‐Cu‐O.

ISSN:0003-6951    

DOI:10.1063/1.103335

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We introduce an electrostatic lens for ballistic electrons in two‐dimensional (2D) systems and demonstrate its focusing action in very high mobility GaAs‐(AlGa)As heterostructures. This is the first refractive element for the control of 2D electrons. It exemplifies the close analogy between ballistic propagation in 2D electron systems and traditional geometrical optics.

ISSN:0003-6951    

DOI:10.1063/1.102538

出版商:AIP    

年代:1990

数据来源: AIP