Proceedings

EPJ B Highlight - Testing particle scattering and reflection in graphene

Band structures for the left and right ferromagnetic regions. Credit: W. Yan., et al., EPJ B (2023)

Testing the quantum effects of Andreev reflection in the wonder material could have positive implications for quantum technology

Humanity stands on the verge of two major revolutions: the boom in 2-dimensional supermaterials like graphene with incredible properties and the introduction of quantum computers with processing power that vastly outstrips standard computers.

Understanding materials like graphene, made of single sheets of atoms, means better investigations of the properties they display at an atomic level. This includes how electrons behave around superconductors — materials that, when cooled to temperatures near absolute zero, can conduct electricity without energy loss.

When a superconductor is sandwiched between metal materials, a type of scattering called crossed Andreev reflection may appear, and in an s-wave superconductor junction, the Andreev reflection usually induces correlated opposite spin in electrons. This can be used to induce entanglement, a quantum phenomenon that is critical for quantum computers.

In a new paper in EPJ B, author Rui Shen, from the National Laboratory of Solid State Microstructures and School of Physics at Nanjing University, China, and his co-authors theoretically assess nonlocal transport and crossed Andreev reflection in a ferromagnetic s-wave superconductor junction composed of the gapped graphene lattices.

“A staggered potential can be induced by growing the ferromagnetic graphene on the boron nitride substrate, leading to the symmetry breaking and the fully spin-polarized electron state,” Shen says. “The Fermi level is properly tuned via gate voltage or doping so that it crosses only one conduction band in the left lead and one valence band in the right lead.”

Shen explains that the team predicted a pure equal-spin crossed Andreev reflection signal in the antiparallel configuration of the ferromagnetic exchange fields of two leads and a pure opposite-spin CAR signal in the parallel configuration.

“The equal-spin and opposite-spin correlations can be easily switched by swapping the exchange fields. The pure equal-spin signal here is absent in the gapless graphene junction,” he continues. “The pure equal-spin crossed Andreev reflection (opposite-spin crossed Andreev reflection) in our model is achieved not only at the Dirac point but over a large voltage range, suggesting the highly efficient nonlocal splitting of the Cooper pairs with spin-triplet (spin-singlet) pairing correlations.”

Shen adds that the time-reversed process of the CAR is called the Cooper pair splitting, and it represents one of the effective ways to obtain entangled states in quantum systems.

“This may have significant applications in quantum communication and quantum computation,” he concludes.

This was our first experience of publishing with EPJ Web of Conferences. We contacted the publisher in the middle of September, just one month prior to the Conference, but everything went through smoothly. We have had published MNPS Proceedings with different publishers in the past, and would like to tell that the EPJ Web of Conferences team was probably the best, very quick, helpful and interactive. Typically, we were getting responses from EPJ Web of Conferences team within less than an hour and have had help at every production stage.
We are very thankful to Solange Guenot, Web of Conferences Publishing Editor, and Isabelle Houlbert, Web of Conferences Production Editor, for their support. These ladies are top-level professionals, who made a great contribution to the success of this issue. We are fully satisfied with the publication of the Conference Proceedings and are looking forward to further cooperation. The publication was very fast, easy and of high quality. My colleagues and I strongly recommend EPJ Web of Conferences to anyone, who is interested in quick high-quality publication of conference proceedings.

On behalf of the Organizing and Program Committees and Editorial Team of MNPS-2019, Dr. Alexey B. Nadykto, Moscow State Technological University “STANKIN”, Moscow, Russia. EPJ Web of Conferences vol. 224 (2019)

ISSN: 2100-014X (Electronic Edition)

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