Trinity-led study makes discovery that could shock you in reverseVish Gainon April 19, 2022 at 13:12 Silicon RepublicSilicon Republic

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Scientists in Dublin and Madrid have made some peculiar discoveries that seem to go against one of the most fundamental laws of physics – the second law of thermodynamics.

While energy always moves from hotter regions to colder regions, in accordance with the law, the scientists have found an exception to this rule in certain materials, described as trivial and non-trivial topological systems, through which electricity flows from colder to hotter regions.

A trivial system is an object through which electricity can flow without needing to split or loop in any part, such as in a ball. An example of a non-trivial system would be a donut or a teacup, both of which have loops that cause a diversion in the straight flow of electricity.

The study, published in the journal Physical Review Letters last month, is concerned with ‘robust edge currents’ – which exhibit the unconventional behaviour. While known for a long time, robust edge currents were until now only associated with non-trivial systems.

“The existence of edge currents in topologically non-trivial materials has been known and understood for decades,” observed Prof Mark Mitchison, assistant professor at Trinity’s School of Physics and lead author of the study. “But we didn’t expect to see robust edge currents appear in topologically trivial systems as well.”

Energy efficient processors

Mitchison, along with his colleagues Prof. Ángel Rivas and Miguel-Ángel Martin Delgado from Universidad Complutense of Madrid, found that the counterintuitive current is remarkably robust and arises in a wider class of materials than was previously believed.

They also found that for the robust edge currents can happen in trivial systems when the object has a temperature gradient, meaning that different parts of the object are at different temperatures.

The finding makes it easier to observe the phenomenon in experiments and could potentially lead to the development of new methods to control the flow of energy through nanoscale structures – leading to advancements in materials science and powerful, sustainable computing.

For example, further study of this phenomenon in more geometrically complex structures used in real electronic devices can help scientists design more energy efficient processers or circuit elements that can recycle wasted heat.

No rules broken

While electricity flows in the ‘wrong’ directions in certain instances, the net transfer of heat from one part to another is always in compliance with the laws of physics, however.

“The overall, net transfer of heat is always from the hot to the cold reservoir. The second law of thermodynamics is never violated,” clarified Mitchison. “But locally, on one edge, the current flows in the other direction so a being that lives on that surface would observe very strange physics!” he added.

“The current would be flowing the wrong way from their perspective, almost like watching a movie in reverse.”

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