Based on the Green's function method, we study theoretically the pair correlations and the local density of states (DOS) in a ferromagnet/ferromagnet/s-wave superconductor (F1F2S) heterostructure in the clean limit. The Green's functions which satisfy the Gor'kov equations are calculated numerically without taking the quasiclassical approximation. We find that, when the angle α between the exchange fields in F1 and F2 is finite (α≈0.5π) and further F1 is a half-metal, only the equal-spin triplet correlation can be induced within the F1 layer. In this circumstance, the Andreev reflection is governed by the anomalous equal-spin-band Andreev reflection which can lead to a zero-energy Andreev bound state in the F2 layer. In the presence of the zero-energy Andreev bound state, the induced DOS in the F1 layer exhibits a rather sharp zero-energy peak (ZEP). We derive the condition for the occurrence of the zero-energy Andreev bound state analytically and verify that it can predict the numerical results excellently. In particular, we find that the ZEP structure of DOS can penetrate deep into the F1 layer reflecting the long-range nature of the equal-spin triplet correlation. Experimental detection of the long-range ZEP in our F1F2S system (by using STM, for instance) may provide unambiguous evidence for the presence of the long-range triplet pair correlation induced by the superconducting proximity effect.
CHEN Chao
,
JIN Biao
. Long-range pair correlations and the Andreev bound state in ferromagnet/ferromagnet/superconductor junctions[J]. Journal of University of Chinese Academy of Sciences, 2023
, 40(4)
: 456
-467
.
DOI: 10.7523/j.ucas.2021.0072
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