Researchers build a quantum dot energy recuperator

In recent years, thermoelectric generators have been the subject of a growing number of studies because of their ability to convert lost heat into electrical energy. Quantum dots, semiconductor crystals with distinct conductive properties, may be good candidates for thermoelectric generation because their distinct resonance levels provide excellent energy filters.

In a recent study, researchers at the University of Cambridge, together with colleagues from Madrid, Rochester, Duisburg and Sheffield, experimentally demonstrated the potential of an autonomous energy recuperator at the nanoscale based on resonant tunneling quantum dots. This harvester is based on previous research done by part of their team, which proposed a three-terminal energy harvester based on two resonant tunneling quantum dots with different energy levels.

The energy recovery device was performed at Cambridge's Cavendish laboratory by a researcher named Gulzat Jaliel. Andrew Jordan presented the initial theoretical proposal for the device in 2013, and theoretical work at the origin of the harvester was carried out by him in collaboration with the renowned semiconductor physicist Markus Büttiker and a post team -doctorants in Geneva.

"Since the document of my colleagues Rafa and Markus on the points blocked by Coulomb, I started to think about the thermoelectric in the mesoscopic circuits," said Jordan Phys.org, one of the researchers who developed the theory behind the harvesting system. "During my sabbatical in Geneva in 2010-2011, we reflected and calculated on the chaotic cavity heat engine with quantum dot contacts and I ended up publishing another article with Björn and Rafa."

The device proposed earlier by Jordan and some of his colleagues, however, provided for a weak power. In the summer of 2013, therefore, when he returned to Geneva for a brief visit, Mr. Jordan began to further explore the relationship between the resonant tunnel and thermoelectricity. His hunch was that a device using resonant quantum dots would have greater power and high efficiency.

"I remember very well sitting in my hotel room on a Saturday in Geneva, playing with the equations, and realizing that if we just gave the cavity its own temperature and its own chemical potential then everything would become very simple and we would have gotten a nice result.At each energy interval captured by the electron, a single charge of electrons was transported and the load balances and d & # 39; Energy was simple, "said Jordan. "In principle, scaling would also be simple.I have written the results with Björn and Rafa, and Markus, of course, and the rest belongs to the story."

The recent study began when Jaliel's Ph.D. supervisor, Professor Charles G. Smith, advised him to try the experimental realization of the quantum dot energy collector as part of his dissertation and she decided to try it. His project also inspired earlier research by Dr. Jonathan Prance at Cavendish Lab, in which he used a similar device to demonstrate a refrigerator, highlighting the dual role of these devices.

In their recent experiments, Jaliel and his colleagues have essentially built an energy recuperator by placing two quantum dots next to a central cavity. They then controlled the energy levels of each point by applying different voltages to their respective piston valves and heated the cavity by supporting alternating currents in the neighboring channel.

The harvester developed by Jaliel and his collaborators can, at least in principle, achieve the effectiveness of Carnot. In addition, it can be optimized to achieve high power associated with high efficiency at maximum power.

"When the energy of the electrons matches the energy of the quantum dots, they can enter or exit the cavity through the dots," said Gulzat Jaliel, one of the researchers who led the study. study at Phys.org. "When the electrons enter the hot cavity through a point of lower energy level and exit through the higher energy level one, they must absorb a certain amount of energy from the cavity in order to be able to complete the process and thus generate some heat power from the heat cavity autonomously. "

This experimental set-up allowed researchers to build the new energy recuperator. However, in real-world applications, the cavity used in their study could be warmed up with the help of various other sources, including lost heat from other quantum devices.

It is interesting to note that the energy recovery device presented by Jaliel, Jordan and their colleagues could serve as a green energy source when scaled in the millions or billions, since the amount of energy lost it would reap would also increase. Another advantage of this quantum dot-based system is that it could be used to charge other devices in situations where the power supply is low, such as satellites in places with high temperature gradients.

"The main purpose of our experiment was to demonstrate that the theoretical proposition is achievable and reliable," said Jaliel. "Any other industrial application will be very interesting to see too."

Other teams of researchers have already built similar energy recuperators. An example is a harvester by Holger Thierschmann et al., Also based on an earlier study by Sánchez and Büttiker. However, compared to this harvester previously developed, the device made by Jaliel and his colleagues is easier to control, while offering increased power and efficiency.

When collecting measurements at an estimated base temperature of 75 mK in a He³/He⁴ refrigerator, in fact, this new quantum dot energy recuperator can generate a remarkable thermal power of 0.13 fW for a temperature difference of about 67 mK from a point to the l '. other of each point. In their future studies, the researchers plan to explore three possible strategies to further improve the performance of the faller. First, they would like to redefine the points to better control the tunneling speeds, then enlarge the device and improve its operating temperature.

"More precise control of point tunneling rates should help achieve near ideal Carnot efficiency," said Jaliel. "Resonant tunneling quantum wells would increase this power, as also predicted by the theoretical part of another study by Björn Sothmann, Rafael Sánchez, Andrew N. Jordan, and Markus Büttiker." I tried to do this experimentally during my thesis D. to study, but unfortunately I ran out of time before finishing it, I would really like to try again if I have the chance. "

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