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The thin-film coating protects against oxidation that can disrupt superconductivity and quantum coherence. Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory found that adding a
The thin-film coating protects against oxidation that can disrupt superconductivity and quantum coherence. Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory found that adding a layer of magnesium improved the properties of tantalum, a superconducting material that has shown promise in creating qubits, the basis of quantum computers.
As described in a newly published article in the journal Advanced Materials A thin layer of magnesium prevents tantalum from oxidizing, increases its purity and raises the temperature at which it operates as a superconductor. All three can enhance tantalum’s ability to store quantum information in qubits.
This work builds on previous research in which a team from Brookhaven’s Center for Functional Nanomaterials (CFN), Brookhaven’s National Synchrotron Light Source II (NSLS-II), and Princeton University sought to understand the attractive properties of tantalum and then worked with scientists in the Department of Concentration It endures. Theorists at Media Physics and Materials Science (CMPMS) at Brookhaven and the Department of Energy’s Pacific Northwest National Laboratory (PNNL) to uncover details about how the material oxidizes.
These studies have shown why oxidation is a problem.
“When oxygen reacts with tantalum, it forms an amorphous insulating layer that absorbs tiny energy particles from the current flowing through the tantalum lattice. This loss of energy disrupts quantum coherence, a material’s ability to keep quantum information in a coherent state,” said CFN scientist Mingzhao Liu, lead author of the previous research and the new paper. explained.
Although oxidation of tantalum is generally self-limiting (the main reason for its relatively long consistency time), the team wanted to explore strategies to further suppress oxidation to see if they could improve the material’s performance.
“The reason tantalum oxidizes is because you have to work with it in air, and the oxygen in the air reacts with the surface,” Liu explained. “So is there anything we as chemists can do to stop this process? “One strategy is to find something to hide it in.”
All this work is carried out within the framework of the Joint Design Center for Quantum Advantage (C). 2 QA), National Quantum Information Research Center led by Brookhaven. While ongoing research examines different types of coating materials, a new paper describes a promising first approach: coating tantalum with a thin layer of magnesium.
“When you make tantalum film, it’s always in a high-vacuum room, so there’s not a lot of oxygen to speak of,” Liu said. “The problem always occurs when you remove it. So we thought we could lay down a layer of tantalum, without breaking the vacuum, and then maybe put another layer on top, like magnesium, to prevent the surface from interacting with air.”
Studies using transmission electron microscopy to image the structural and chemical properties of the material atomic layer by atomic layer showed that the strategy of coating tantalum with magnesium was extremely successful. The magnesium formed a thin layer of magnesium oxide on the surface of the tantalum, which appeared to block the penetration of oxygen.
Chenyu Zhou, a research associate at Brookhaven National Laboratory’s Center for Functional Nanomaterials (CFN) and first author of the study, collaborated with Mingzhao Liu (CFN), Yimei Zhu (CMPMS), and Junsik Moon (CFN and CMPMSD) on the DynaCool Physical Properties Measurement System at CFN ( PPMS). The team used this tool to produce tantalum thin films with and without a protective magnesium layer; they were thus able to determine whether the magnesium coating minimized tantalum oxidation. Credits: Jessica Rotkiewicz/Brookhaven National Laboratory
“Electron microscopy techniques developed in Brookhaven’s laboratory allowed us to directly visualize not only the chemical distribution and arrangement of atoms in the thin magnesium coating layer and tantalum film, but also changes in their oxidation states,” said study co-author Yimei Zhu. to work. From CMPMS. “This information is extremely valuable for understanding the electronic behavior of the material,” he said.
X-ray photoelectron spectroscopy studies on NSLS-II revealed the effect of magnesium coating on limiting tantalum oxide formation. Measurements showed that an extremely thin layer of tantalum oxide (less than one nanometer thick) remained confined just below the magnesium-tantalum interface without disturbing the rest of the tantalum lattice.
“This is in stark contrast to uncoated tantalum, where the tantalum oxide layer can be thicker than three nanometers, significantly degrading the electronic properties of the tantalum,” said Andrew Walter, Soft’s chief scientist and co-author of the study. X-ray Scattering and Spectroscopy Program at NSLS-II.
The PNNL team then used atomic-scale computational simulations to determine the most likely arrangement and interaction of the atoms based on their binding energies and other properties. These simulations helped the team develop a mechanistic understanding of why magnesium works so well.
At the simplest level, calculations showed that magnesium has a higher affinity for oxygen than tantalum.
“Although auxin has a high affinity for tantalum, it is ‘happier’ to stay with magnesium than to stay with tantalum,” said Peter Sushko, one of the theorists at PNNL. “So magnesium reacts with oxygen to form a protective layer of magnesium oxide. You don’t even need that much magnesium to get the job done. A magnesium thickness of just two nanometers almost completely blocks tantalum oxidation.”
The scientists also showed that the protection was long-lasting: “Even after a month, the tantalum is still pretty good. Magnesium is a really good oxygen barrier,” concluded Liu.
Magnesium had an unexpected beneficial effect: it “scrubbed” unwanted impurities from the tantalum and consequently raised the temperature at which it operated as a superconductor.
“Although we create these materials in vacuum, there are always traces of gases such as oxygen, nitrogen, water vapor, hydrogen. And tantalum absorbs these impurities very well,” Liu explained. “No matter how careful you are, these impurities will always be in your tantalum.”
But when scientists added a magnesium coating, they found that its strong affinity for impurities pushed them out. The resulting purer tantalum had a higher superconducting transition temperature. This could be crucial for applications, as most superconductors need to be very cold to work. Under these extremely cold conditions, most conduction electrons pair up and move through the material without resistance.
“Even a small increase in the transition temperature can reduce the number of remaining unpaired electrons,” Liu said, potentially making the material a better superconductor and increasing the quantum coherence time.
“More research will be needed to see whether this material improves the performance of qubits,” Liu said. “But this work provides valuable information and new material design principles that could help pave the way for large-scale, high-performance quantum computing systems.”
Source: Port Altele
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