New understanding of the limits on nano-noise

The image illustrates a tiny nanoscale heat engine connecting hot and cold sides. The temperature difference drives a current, generating power, but both current and power are noisy hindering precise and reliable performance. The Chalmers researchers have managed to demonstrate a trade-off relation between noise and power from these nanoscale engines, paving the way for future nanoscale thermoelectric devices with high precision. Illustration: Carina Schultz, Chalmers University of Technology.

Nanotechnology is rapidly advancing, capturing widespread interest across industries
such as communications and energy production. At the nano level - equivalent to a
millionth of a millimeter - particles adhere to quantum mechanical laws. By harnessing
these properties, materials can be engineered to exhibit enhanced conductivity,
magnetism, and energy efficiency.

"Today, we witness the tangible impact of nanotechnology - nanoscale devices are
ingredients to faster technologies and nanostructures make materials for power
production more efficient," says Janine Splettstoesser, Professor of Applied Quantum
Physics at Chalmers.

Devices smaller than the human cell unlocking novel electronic and
thermoelectric properties

To manipulate charge and energy currents down to the single-electron level,
researchers use so-called nanoscale devices, systems smaller than human cells. These
nanoelectronic systems can act as "tiny engines" performing specific tasks, leveraging
quantum mechanical properties.

"At the nanoscale, devices can have entirely new and desirable properties. These
devices, which are a hundred to ten thousand times smaller than a human cell, allow to
design highly efficient energy conversion processes," says Ludovico Tesser, PhD student
in Applied Quantum Physics at Chalmers University of Technology.

Navigating nano-noise: a crucial challenge

However, noise poses a significant hurdle in advancing this nanotechnology research.
This disruptive noise is created by electrical charge fluctuations and thermal effects
within devices, hindering precise and reliable performance. Despite extensive efforts,
researchers have yet to find out to which extent this noise can be eliminated without
hindering energy conversion, and our understanding of its mechanisms remains limited.
But now a research team at Chalmers has succeeded in taking an important step in the
right direction.

In their recent study, published as editor's suggestion in Physical Review
Letters, they investigated thermoelectric heat engines at the nanoscale. These
specialised devices are designed to control and convert waste heat into electrical
power.

"All electronics emit heat and recently there has been a lot of effort to understand how,
at the nano-level, this heat can be converted to useful energy. Tiny thermoelectric heat
engines take advantage of quantum mechanical properties and nonthermal effects and,
like tiny power plants, can convert the heat into electrical power rather than letting it go
to waste," says Professor Splettstoesser.

Balancing noise and power in nanoscale heat engines

However, nanoscale thermoelectric heat engines work better when subject to
significant temperature differences. These temperature variations make the already
challenging noise researchers are facing even trickier to study and understand. But now,
the Chalmers researchers have managed to shed light on a critical trade-off between
noise and power in thermoelectric heat engines.

"We can prove that there is a fundamental constraint to the noise directly affecting the
performance of the "engine. For example, we can not only see that if you want the
device to produce a lot of power, you need to tolerate higher noise levels, but also the
exact amount of noise. It clarifies a trade-off relation, that is how much noise one must
endure to extract a specific amount of power from these nanoscale engines. We hope
that these findings can serve as a guideline in the area going forward to design
nanoscale thermoelectric devices with high precision," says Ludovico Tesser.

More about the research:
The study "Out-of-Equilibrium Fluctuation-Dissipation Bounds" was published in
Physical Review Letters, on 3 May 2024

Funding:
The research project has been funded by the European Research Council (ERC) under the European Union's Horizon Europe research and innovation program (101088169/NanoRecycle), as well as by a Wallenberg Academy Fellowship.

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Updated 17 September 2024, 07:12Published 17 September 2024, 07:00

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