Unconventional long range triplet proximity effect in planar YBa₂Cu₃O₇/La_0.7Sr_0.3MnO₃/YBa₂Cu₃O₇ Josephson junctions

Abstract

Proximity effect between superconductors and ferromagnets may become long range due to the generation of triplet pairs. The recent finding of a long one micron-range unconventional Josephson effect between YBa2Cu3O7 High Tc cuprates separated by a half metallic La0.7Sr0.3MnO3 manganite ferromagnet has uncovered a novel unconventional triplet proximity effect. In this paper we examine the temperature dependence of the critical current of planar Josephson junctions. We find that the critical current –normal resistance product follows the predictions of traditional superconductor-normal metal-superconductor junctions which implies that triplet pairs in a ferromagnet are transported in the diffusive limit similarly to singlet pairs in a normal metal. This result calls for theoretical studies of the new triplet Josephson effect and underlines its potential in future superconducting spintronics.

Size-Dependence and High Temperature Stability of Radial Vortex Magnetic Textures Imprinted by Superconductor Stray Fields

“…Second, there are no FM regions in between superconducting islands, and therefore also no dipolar fields originating in these regions which could compete with the SC magnetic stray field. However, we observe no imprint for ⊡ SC 20 /FM Ø structures with Ø < 5 μm, nor for ⊙ SC 20 /FM Ø structures with Ø < 2 μm, yet the SC stray magnetic field generated by Ø = 20 μm structures should allow the magnetic imprint (see Supporting Information, Section 4). Indeed, micromagnetic modeling show that the stray field originating from ⊙ SC 20 structures could allow the imprint of magnetic radial vortices in Py down to a lateral size of 900 nm (Supporting Information, Section 3).…”

“…The stability of the imprint as the temperature is increased above the SC transition has been investigated by obtaining XMCD images as a function of temperature after a superconducting imprint at 50 K for ⊡ SC 20 /FM cont and ⊡ SC 20 /FM 20 structures. Fine details concerning the relaxation of the imprinted magnetic domain depend on the particularities of each structure, namely, the distribution of defects.…”

“…The nonvanishing XMCD signal above T C indicates that imprinted domains do not relax to a conventional vortex pattern configuration or multidomain state once the SC stray-field vanishes. Inset panels a−e depict XMCD images obtained for one of the ⊡ SC 20 /FM cont structures. At 80 K, close to T C (89 K), there is a partial relaxation of the imprinted magnetic domain state, as evidenced by the appearance of dendritic domains and an overall change of the XMCD strength.…”

“…The second type consists of samples where the Py has been structured with the same shape but with sizes smaller than that of the SC microstructure underneath (20 μm). From now on, we will use the notation (⊡, ⊙)SC Ø /FM cont to refer to (square or circular) structures with continuous Py layer and variable SC element size and (⊡, ⊙)SC 20 /FM Ø to refer to structures with structured Py on top of 20 μm SC islands, respectively. The superscript Ø indicates the lateral size of the SC or FM in μm, as well as the size of imprinted magnetic domains.…”

“…Superconductivity and ferromagnetism are two electronic ground states which, despite their antagonistic character, may become synergistic in superconductor/ferromagnet hybrids. They yield exciting responses as, for example, the recently demonstrated long-range supercurrent and Josephson effects driven by equal spin triplet superconducting correlations − which coexist with ferromagnetism.…”