University Park, Pennsylvania – Quantum technology has a major problem. It’s small. Characteristic properties present at the subatomic scale usually disappear at macroscopic scales, making it difficult to take advantage of the excellent sensing and communication capabilities of real-world applications, such as optical systems and advanced computing. However, an international team, led by physicists from Pennsylvania and Columbia University, has now developed a new approach to maintain special quantum properties, even in three-dimensional (3D) materials.
The researchers published their survey results in natural materials today (February 19th).
“The functionality displayed by two-dimensional (2D) materials is enormous and the possibilities are innovative, but maintaining superior properties beyond the 2D limit remains a horrifying challenge,” says Pennsylvania Physics. says Yinming Shao, assistant professor of education. Such materials are crystals that are usually one atom thick and can be applied to a variety of fashions, including flexible electronics, energy storage, and quantum technology. “Therefore, realising, understanding and control of nanoscale confinement is important for both quantum physics and the exploration of future quantum technologies.”
The team examined semiparticles called excitons in semiconductor materials, which have unique optical properties and can carry energy without charge. Ubiquitous semiconductors across computers, mobile phones and other electronic devices introduce power under certain conditions and inhibit them under other conditions. Excitons are generated when light hits a semiconductor, activates electrons and jumps to the next energy level. The resulting excitation electrons and the holes they leave are jointly referred to as excitons. Excitons occur homogeneously across typical 3D semiconductors such as silicon.
“However, the binding energy of excitons in bulk materials such as silicon is usually small, and it is not very stable and is not easy to observe,” Xiao said.
The traditional method for preparing 2D materials was developed in 2004 and led to the discovery of graphene, a single layer of highly conductive carbon that is stronger than steel. The process is simple, but labor intensive as each layer must be peeled off from the bulk crystals by applying adhesive tape and peeling it off.
In this thin 2D state, the excitation tool can carry energy without charge, and emit light when it recombs with the hole. However, to preserve their properties in materials large enough for such applications, researchers must generate a huge number of layers.
To do this without manually peeling and stacking each layer, researchers relied on magnetism, another aspect of physics. Specifically, co-author Xavier Roy, a professor of chemistry at Columbia University, focuses on chromium bromide bromide (CRSBR), a layered magnetic semiconductor that has been further researched and developed since 2020.
At room temperature, CRSBR functions as a normal semiconductor, like silicon. Cooling the CRSBR to approximately -223°F will result in the ground state, or lowest energy state. This converts magnetic moments (usually called “spin”) into antiferromagnetic systems where the particles of the system are aligned in a normal, repetitive pattern. In particular, with CRSBR, this antiferromagnetic order allows each layer to alternate magnetic alignment, effectively cancelling the magnetic moments and insensitive the material to external magnetic forces. As a result, excitations tend to stay in the layer at the same spin rather than hooping to adjacent layers at opposite spins. Like alternating cars on one-way street, these established boundaries are confined to layers that share the same spin direction.
“This is an effective approach to creating a single layer of atomic material without peeling off, while still preserving a sharp interface,” Shao says. “This means that the same behavior of limited excitons can be achieved as demonstrated in 2D materials of bulk materials.”
Using optical spectroscopy, theoretical modeling, and calculations, the researchers determined that this magnetic confinement would be harder regardless of how many layers in the system, including the surface layer.
“We did a lot of work to make sure this was true,” Xiao said.
Shao’s team’s findings were supported by another research group in Germany, Florian Dirnberger and Alexey Chernikov of the Tud Dresden Institute of Technology. Shao said the two groups decided to compare the notes and found that they all reached the same conclusion.
“Our data line up very well, which is noteworthy as we used two different crystalline materials in different labs,” says Shao. “We wrote this joint paper because our results are consistent with one another and are in good agreement with our theoretical predictions.”
The alignment results arise from the use of magnetism, van der Waals interactions and exciton behavior to achieve quantum confinement between optical systems and potential applications to advance quantum technology, according to Shao. I did.
“The marriage of these different aspects of physics was an important aspect of this discovery,” Xiao said.
Shao completed his PhD and postdoc fellowship at Columbia University. Other contributors include Siyuan Chiu, Evan J. Telford, Brian Sim, Francesco L. Luta, Andrew J. Mills, Daniel G. Chica, Avalon H. DiDuxe and Michael E. Ziebel, Iping Wang, Yonghaon Cho, Young Zhu Be, Xiaoyang Zhu, Xavier Roy and DN Basov, Columbia University; Florian Dirunberger, Sofia Terres, Alexei Chernikov, Tehd Dresden Institute of Technology, Germany. Swagata Acharya and Rupert Huber, National Institute of Renewable Energy. Dimiter Pashov, King’s College London, England. Mikhail I. Katznelson, University of Ladboud, Netherlands. Kseniia Mosina and Mark Van Schilfgaarde, University of Chemistry Prague, Czech Republic. Zdenek Sofer from the University of Regensburg, Germany. Dirnberger is also affiliated with the Institute of Technology Munich. Kim is also a member of the University of Arizona. Mills is also a member of the Flatiron Institute. A complete list of authors and their affiliations may be found in the paper.
The US Department of Energy, the European Research Council, the US National Science Foundation, the outstanding outstanding cluster of excellence on complexity and topology in quantum materials, and the Emmy Nortel program supported this work.
