Material Keyboard

The fabric keyboard realized by the ETH Zurich researchers. By making use of electrical voltages (“keys”) at totally different factors, the magic-​angle graphene can turn out to be regionally superconducting (electron pairs) or isolating (barrier on the correct). Credit score: ETH Zurich / F. de Vries

Researchers at ETH Zurich have succeeded in turning specifically ready graphene flakes both into insulators or into superconductors by making use of an electrical voltage. This method even works regionally, which means that in the identical graphene flake areas with utterly totally different bodily properties may be realized facet by facet.

The manufacturing of recent digital elements requires supplies with very numerous properties. There are isolators, for example, which don’t conduct electrical present, and superconductors which transport it with none losses. To acquire a selected performance of a part one often has to affix a number of such supplies collectively. Typically that’s not straightforward, particularly when coping with nanostructures which can be in widespread use at present.

A group of researchers at ETH Zurich led by Klaus Ensslin and Thomas Ihn on the Laboratory for Strong State Physics have now succeeded in making a cloth behave alternately as an insulator or as a superconductor – and even as each at totally different areas in the identical materials – by merely making use of an electrical voltage. Their outcomes have been printed within the scientific journal Nature Nanotechnology. The work was supported by the Nationwide Centre of Competence in Analysis QSIT (Quantum Science and Expertise).

Graphene with a magic angle

The fabric Ensslin and his co-​employees use bears the considerably cumbersome identify “Magic Angle Twisted Bilayer Graphene.” In precise truth, this identify hides one thing quite easy and well-​identified, particularly carbon – albeit in a selected kind and with a particular twist. The place to begin for the fabric are graphene flakes, that are carbon layers which can be just one atom thick. The researchers put two of these layers on high of one another in such a manner that their crystal axes are usually not parallel, however quite make a “magic angle” of precisely 1.06 levels. “That’s fairly difficult, and we additionally must precisely management the temperature of the flakes throughout manufacturing. In consequence, it usually goes improper,” explains Peter Rickhaus, who was concerned within the experiments as a postdoc.

In twenty p.c of the makes an attempt, nevertheless, it really works, and the atomic crystal lattices of the graphene flakes then create a so-​referred to as moiré sample by which the electrons of the fabric behave in another way than in abnormal graphene. Moiré patterns are acquainted from tv, for example, the place the interaction between a patterned garment and the scanning strains of the tv picture can result in fascinating optical results. On high of the magic angle graphene flakes the researchers connect a number of further electrodes which they will use to use an electrical voltage to the fabric. Once they then cool all the pieces down to some hundredths of a level above absolute zero, one thing outstanding occurs. Relying on the utilized voltage, the graphene flakes behave in two utterly reverse methods: both as a superconductor or as an insulator. This switchable superconductivity was already demonstrated in 2018 on the Massachusetts Institute of Expertise (MIT) within the USA. Even at present just a few teams worldwide are capable of produce such samples.

Josephson Junction

Electron microscope picture of the Josephson junction (false colors). Utilizing the electrodes (brilliant and darkish gold) as piano keys, an insulating layer solely 100 nanometres thick may be created between the 2 superconducting areas. Credit score: ETH Zurich / F. de Vries

Insulator and superconductor in the identical materials

Ensslin and his colleagues are actually going one step additional. By making use of totally different voltages to the person electrodes they flip the magic angle graphene into an insulator in a single spot, however a number of hundred nanometres to at least one facet it turns into a superconductor.

“After we noticed that, we clearly first tried to understand a Josephson junction,” says Fokko de Vries, who can also be a postdoc in Ensslins laboratory. In such junctions two superconductors are separated by a wafer-​skinny insulating layer. On this manner, present can’t circulation straight between the 2 superconductors however quite has to tunnel quantum mechanically via the insulator. That, in flip, causes the conductivity of the contact to range as a perform of the present in a attribute vogue, relying on whether or not direct or alternating present is used.

Attainable purposes in quantum applied sciences

The ETH researchers managed to supply a Josephson junction contained in the graphene flakes twisted by the magic angle by utilizing totally different voltages utilized to the three electrodes, and likewise to measure its properties. “Now that that’s labored as properly, we will strive our palms at extra advanced units similar to SQUIDs,” says de Vries. In SQUIDs (“superconducting quantum interference gadget”) two Josephson junctions are linked to kind a hoop. Sensible purposes of such units embody measurements of tiny magnetic fields, but in addition fashionable applied sciences similar to quantum computer systems. For attainable makes use of in quantum computer systems, an fascinating facet is that with the assistance of the electrodes the graphene flakes may be turned not simply into insulators and superconductors, but in addition into magnets or so-​referred to as topological insulators, by which present can solely circulation in a single path alongside the sting of the fabric. This could possibly be exploited to understand totally different sorts of quantum bits (qubits) in a single gadget.

A keyboard for supplies

“Up to now, nevertheless, that’s simply hypothesis,” Ensslin says. Nonetheless, he’s enthusiastic in regards to the prospects that come up from {the electrical} management even now. “With the electrodes, we will virtually play the piano on the graphene.” Amongst different issues, the physicists hope that this can assist them to achieve new insights into the detailed mechanisms that result in superconductivity in magic angle graphene.

Reference: “Gate-defined Josephson junctions in magic-angle twisted bilayer graphene” by Folkert Okay. de Vries, Elías Portolés, Giulia Zheng, Takashi Taniguchi, Kenji Watanabe, Thomas Ihn, Klaus Ensslin and Peter Rickhaus, 3 Might 2021, Nature Nanotechnology.
DOI: 10.1038/s41565-021-00896-2

By Rana

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