Green information technologies: Superconductivity meets spintronics


Date:
December 2, 2021
Source:
Helmholtz-Zentrum Berlin fu"r Materialien und Energie
Summary:
Superconducting coupling between two regions separated by a
one micron wide ferromagnetic compound has been proved by an
international team.

This macroscopic quantum effect, known as Josephson effect,
generates an electrical current within the ferromagnetic compound
made of superconducting Cooper-pairs. Magnetic imaging of the
ferromagnetic region at BESSY II has contributed to demonstrate that
the spin of the electrons forming the Cooper pairs are equal. These
results pave the way for low-power consumption superconducting
spintronic-applications where spin-polarized currents can be
protected by quantum coherence.



FULL STORY ==========================================================================
When two superconducting regions are separated by a strip of non- superconducting material, a special quantum effect can occur, coupling
both regions: The Josephson effect. If the spacer material is a half-metal ferromagnet novel implications for spintronic applications arise. An international team has now for the first time designed a material system
that exhibits an unusually long-range Josephson effect: Here, regions
of superconducting YBa2Cu3O7 are separated by a region of half-metallic, ferromagnetic manganite (La2/3Sr1/3MnO3) one micron wide.


==========================================================================
With the help of magneto-transport measurements, the researchers were
able to demonstrate the presence of a supercurrent circulating through
the manganite - - this supercurrent is arising from the superconducting coupling between both superconducting regions, and thus a manifestation
of a Josephson effect with a macroscopic long range.

Extremely rare: Triplett superconductivity In addition, the scientists
explored another interesting property with profound consequences for
spintronic applications. In superconductors electrons pair together
in so-called Cooper pairs. In the vast majority of superconducting
materials these pairs are composed by electrons with opposite spin in
order to minimise the magnetic exchange field which is detrimental for
the stabilisation of superconductivity. The ferromagnet used by the international team has been a half-ferromagnet for which only one spin
type electron is allowed to circulate.

The fact that a supercurrent has been detected within this material,
implies that the Cooper pairs of this supercurrent must be composed by electrons having the same spin. This so-called "triplet" superconductivity
is extremely rare.

Mapping magnetic domains at BESSY II "At the XMCD-PEEM station at BESSY
II, we mapped and measured the magnetic domains within the manganite
spacer. We observed wide regions homogeneously magnetised and connecting
the superconducting regions. Triplet spin pairs can propagate freely in
these," explains Dr. Sergio Valencia Molina, HZB physicist, who supervised
the measurements at BESSY II.

Superconducting currents flow without resistance which make them very
appealing for low-power consumption applications. In the present case
this current is made of electrons with equal spins. Such spin polarised currents could be used in novel superconducting spintronic applications
for the transport (over long distances) and reading/writing of information while profiting from the stability imposed by the macroscopic quantum
coherence of the Josephson effect.

The new device made of the superconducting and ferromagnetic components therefore opens up opportunities for superconducting spintronics and
new perspectives for quantum computing.

========================================================================== Story Source: Materials provided by Helmholtz-Zentrum_Berlin_fu"r_Materialien_und_Energie.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. D. Sanchez-Manzano, S. Mesoraca, F. A. Cuellar, M. Cabero,
V. Rouco, G.

Orfila, X. Palermo, A. Balan, L. Marcano, A. Sander, M. Rocci,
J. Garcia- Barriocanal, F. Gallego, J. Tornos, A. Rivera,
F. Mompean, M. Garcia- Hernandez, J. M. Gonzalez-Calbet, C. Leon,
S. Valencia, C. Feuillet- Palma, N. Bergeal, A. I. Buzdin,
J. Lesueur, Javier E. Villegas, J.

Santamaria. Extremely long-range, high-temperature Josephson
coupling across a half-metallic ferromagnet. Nature Materials,
2021; DOI: 10.1038/ s41563-021-01162-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211202132440.htm

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