%0 Journal Article
%A Visani, Cristina
%A Sefrioui Khamali, Zouhair
%A Tornos Castillo, Javier
%A Villegas Hernández, Javier Eulogio
%A León Yebra, Carlos
%A Briatico, J.
%A Bibes, Manuel
%A Barthelemy, Agnes
%A Santamaría Sánchez-Barriga, Jacobo
%T Equal-spin Andreev reflection and long range coherent transport in hightemperature superconductor/half-metallic ferromagnet junctions
%D 2012
%U https://hdl.handle.net/20.500.14352/97161
%X Conventional superconductivity is incompatible with ferromagnetism, because the magnetic exchange field tends to spin-polarize electrons and breaks apart the opposite-spin singlet Cooper pairs(1). Yet, the possibility of a long-range penetration of superconducting correlations into strong ferromagnets has been evinced by experiments that found Josephson coupling between superconducting electrodes separated afar by a ferromagnetic spacer(2-7). This is considered a proof of the emergence at the superconductor/ferromagnetic (S/F) interfaces of equal-spin triplet pairing, which is immune to the exchange field and can therefore propagate over long distances into the F (ref. 8). This effect bears much fundamental interest and potential for spintronic applications(9). However, a spectroscopic signature of the underlying microscopic mechanisms has remained elusive. Here we do show this type of evidence, notably in a S/F system for which the possible appearance of equal-spin triplet pairing is controversial(10-12): heterostructures that combine a half-metallic F (La0.7Ca0.3MnO3) with a d-wave S (YBa2Cu3O7). We found quasiparticle and electron interference effects in the conductance across the S/F interfaces that directly demonstrate the long-range propagation across La0.7Ca0.3MnO3 of superconducting correlations, and imply the occurrence of unconventional equal-spin Andreev reflection. This allows for an understanding of the unusual proximity behaviour observed in this type of heterostructures(12,13).
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