  We have carried out extensive studies on the self-injection problem in
barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-d
(YBCO). The heterojunctions were grown in situ by sequentially growing LCMO and
YBCO films on <100> LaAlO3 (LAO) substrate using a pulsed laser deposition
(PLD) system. YBCO micro-bridges with 64 microns width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, Ic, was
measured at 77K on both the control side as well as the LCMO side for different
YBCO film thickness. It was observed that while the control side showed a Jc of
~2 x 10E6 A/ cm2 the LCMO side showed about half the value for the same
thickness (1800 A). The difference in Jc indicates that a certain thickness of
YBCO has become 'effectively' normal due to self-injection. From the
measurement of Jc at two different thickness' (1800 A and 1500 A) of YBCO both
on the LAO as well as the LCMO side, the value of self-injection length (at
77K) was estimated to be ~900 A self-injection length has been quantified. A
control experiment carried out with LaNiO3 deposited by PLD on YBCO did not
show any evidence of self-injection.
