Research Bits: Mar. 19

Superconducting loops; redox gating semiconductors; n-type diamond MOSFET.


Superconducting loops

Researchers from University of California San Diego and University of California Riverside propose using superconducting loops to store and transmit information in a method similar to the human brain.

“Our brains have this remarkable gift of associative memory, which we don’t really understand,” said Robert C. Dynes, professor of physics at UC San Diego and president emeritus of the University of California, in a release. “It can work through the probability of answers because it’s so highly interconnected. This computer brain we built and modeled is also highly interactive. If you input a signal, the whole computer brain knows you did it.”

To create the memory, thin films of the high-temperature superconducting material yttrium barium copper oxide (YBCO) were manipulated with a combination of magnetic fields and currents to create a single flux quantum on the loop. When the current was removed, the flux quantum stayed in the loop, acting as information.

To enable associative memory, additional disordered loops of different sizes and patterns were added. Josephson junctions acted as a gate through which the flux quanta could pass, allowing information to be transferred and the associations built.

Distinct circulating current paths in a 4-loop network show the possible switching activity that allow flux to travel between loops. (Credit: Q-MEEN-C / UC San Diego)

The number of memory locations available increases exponentially with more loops: one loop has three locations, but three loops have 27. For this research, the team built four loops with 81 locations. Next, the team plans to expand the number of loops and the number of memory locations. [1]

Redox gating

Researchers from Argonne National Laboratory, University of Chicago, and University of Science and Technology of China suggest a ​“redox gating” technique that can control the movement of electrons in and out of a semiconducting material.

The scientists designed a device that could regulate the flow of electrons from one end to another by applying a voltage across a material that acted as an electron gate. When the voltage reached a certain threshold, roughly half of a volt, the material would begin to inject electrons through the gate from a source redox material into a channel material.

By using the voltage to modify the flow of electrons, the semiconducting device could act like a transistor, switching between more conducting and more insulating states.

“The new redox gating strategy allows us to modulate the electron flow by an enormous amount even at low voltages, offering much greater power efficiency,” said Dillon Fong, materials scientist at Argonne, in a statement. ​“This also prevents damage to the system. We see that these materials can be cycled repeatedly with almost no degradation in performance.”

With the capability to operate in the subvolt regime, the researchers believe the approach could be used to create circuits that act similarly to the human brain and to develop new quantum materials. [2]

N-type diamond MOSFET

Researchers from the National Institute for Materials Science developed what it says is the first n-channel diamond MOSFET, which could serve as the basis for diamond power electronics and ICs designed for harsh environments.

The team was able to grow high-quality monocrystalline n-type diamond semiconductors with smooth and flat terraces at the atomic level by doping diamond with a low concentration of phosphorus. The n-channel diamond semiconductor layer sits atop another diamond layer doped with a high concentration of phosphorus, which reduced source and drain contact resistance. [3]


[1] Uday S. Goteti, Shane A. Cybart, Robert C. Dynes. Collective neural network behavior in a dynamically driven disordered system of superconducting loops. Proceedings of the National Academy of Sciences, 2024; 121 (12)

[2] L. Zhang, C. Liu, H. Cao, A. J. Erwin, D. D. Fong, A. Bhattacharya, L. Yu, L. Stan, C. Zou, M. V. Tirrell, H. Zhou, W. Chen, Redox Gating for Colossal Carrier Modulation and Unique Phase Control. Adv. Mater. 2024, 2308871.

[3] M. Liao, H. Sun, S. Koizumi, High-Temperature and High-Electron Mobility Metal-Oxide-Semiconductor Field-Effect Transistors Based on N-Type Diamond. Adv. Sci. 2024, 2306013.

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