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The discovery of a new quantum phenomenon in nano-sized nickelate materials that urges components to act in unison could have significant benefits to energy-demanding electronics and the development of ‘made to order’ materials.
As humanity’s reliance on silicon-based electronic devices and technology grows exponentially, the demands that these devices place on the world’s finite energy resources increases. Could the solution to this problem be found in a physical phenomenon that has remained hidden?
A paper authored by a University of Geneva team, and published in the journal Nature Materials, details the discovery of a nanoscale material that ‘knows’ how to switch its behavior based on its composition.
These effects arise from materials on the nanoscale that exploit ‘quantum effects’ — specifically the tendency of carefully arranged atoms to act as one. The coupling effect discovered by the team — working in conjunction with researchers at Swiss Federal Institute of Technology in Lausanne (EPFL), the University of Zurich, the Flatiron Institute of New York and the University of Liègeworking — is unprecedented, and could lead to a new generation of electronics with significantly lower power demands.
The phenomenon arises from nickelates — theoretically identified over 20 years ago and suggested as a substance that could be engineered to possess impressive superconducting qualities at room temperature. When this artificial material , which is created when nickel forms a series of mixed oxide compounds with the addition of an atom belonging to so-called ‘rare earth’ elements, in this case, samarium (Sm) , is stacked in nano-sized thin layers, these layers act as one material.
This is significant with nickelates as they are already known for their capacity to switch from an insulator to an electrical conductor at a given temperature. When this transition occurs depends on the composition of the nickelate. When the material is doped with Sm, the jump occurs at around 130 ⁰C. However, if neodymium (Nd) replaced the Sm, the threshold drops to 73 ⁰C. The deformation of the nickelate’s crystalline structure explains this change.
It was in an attempt to learn more about the differences between these two variations of nickelates that the UNIGE researchers discovered their findings.
A Perfectly Arranged ‘Super-Sandwich’
The scientists from UNIGE took the Sm doped nickelate (SmNiO3) and the Nd version of the material (NdNiO3) and arranged them in a lattice-like structure, to study how two materials that undergo a metal-to-insulator transition at different temperatures would interact. They also hoped to gain an insight into the length scale over which these phases can be established. This required depositing repeated layers of SmNiO3 on to layers of NdNiO3 , creating a ‘super-sandwich’ of perfectly arranged atoms.
When the layers were thick, the different compositions of nickelate retained their characteristics , particularly those different transition temperatures. However, when the team stripped the layers back to no more than eight atoms each, the whole sample began to behave like a singular material, with the layers losing that individuality. This opened up the possibility of ‘made-to-order materials.
This composite nickelate retained the ability to switch between insulator and conductor. However, this phase-shift now occurred at a temperature between the two previous transition temperatures. This means one significant ‘jump’ in conductivity rather than two.
This quirk in behavior became more confusing after a follow-up investigation using an electron microscope at the EPFL. The Lausanne-based team discovered deformations in the crystalline structure of the material only spread from the interface point — the point at which the two composite forms of nickelate ‘touched’ — to around two or three subsequent atomic layers.
This implies that the change in transition temperature across the whole material cannot be a result of distortion in the crystalline structure. The further outer-layers, untouched by said deformation, adjust the phase transition temperature accordingly.
As is the case with much of the counter-intuitive behavior displayed in ‘the quantum realm’, this phenomenon is far from mystical.
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The team says that their study shows that maintaining an interface between conducting and insulating regions of a material is energetically ‘expensive.’ This means that when the two layers are thin-enough, they become a single material — a much less energy-expensive state — which is either totally conducting or insulating. They then switch between states controlled by a single temperature. This finding is the key to less energy-demanding electronics, as less energy would be needed by these materials to switch their behavior.
This means that a device that requires many components switching between conducting and isolating phases would need far less power to function. This could have a marked effect on nanotech and portable technology, enabling the use of smaller, more lightweight batteries.
The new way of controlling the properties of electronic structures could play a specific role in the development of materials designed to meet particular needs in electronic devices, including but not limited to technology that has to be operated at specific temperatures.
References and Further Reading
Dominguez. C., Georgescu. A. B., Mundet. B., et al. (2020) ‘Length scales of interfacial coupling between metal and insulator phases in oxides,’ Nature Materials, https://www.nature.com/articles/s41563-020-0757-x.
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