11.
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La
0.7Ca
0.3MnO
3 (LCMO) and YBa
2Cu
3O
7-δ (YBCO) thin films. The heterojunctions were formed
in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO
3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current,
I
c, was measured at 77 K 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
J
c of ∼ 2 × 10
6 A/cm
2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in
J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO
3 deposited by PLD on YBCO did not show any evidence of self-injection.
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