Fj. Owens, ANOMALY IN MAGNETIC-FIELD DEPENDENCE OF MICROWAVE-ABSORPTION AT VORTEX PINNING TO DEPINNING TRANSITION IN BI2-XPBXSR2CA2CU3O10 SUPERCONDUCTOR, Physics letters. A, 177(2), 1993, pp. 156-160
Previous measurements have shown that the pinning to depinning transit
ion of vortices in the copper oxide superconductors can be observed at
constant temperature by a change in the slope of the linear dependenc
e of the microwave absorption on square-root B at a field B'. In this
work measurements of the magnetic field dependence of the microwave ab
sorption in N = 3 Bi-Pb-Sr-Ca-Cu-O at 9.2 GHz at constant temperature
at small magnetic field intervals in the transition region reveal a ma
rked departure from the square-root B dependence. On the other hand me
asurements of the temperature dependence of the microwave absorption d
ue to vortex dissipation at constant magnetic field at one degree temp
erature intervals show an abrupt transition inconsistent with a second
order character required for a transition from a vortex glass to a fl
uid. The anomaly in the magnetic field dependence of the absorption at
the depinning to pinning transition is shown to be consistent with a
magnetic field dependent distribution of pinning barriers in the flux
solid leading to an intermediate phase consisting of a mixture of vort
ex fluid and solid.