Unique Quantum Material Could Enable Incredibly Powerful, Ultra-Compact Computers

Chemists and physicists at Columbia University have discovered a relationship between tunable electrical and magnetic properties in a 2D semiconductor, with possible applications in spintronics, quantum computing, and fundamental research.

In computers, information is transferred by electrons moving through semiconductors and stored in magnetic materials in the direction of electron spin. Researchers are looking for new materials that combine both quantum features to downsize devices while boosting their performance, which is the goal of an emerging discipline called spintronics ("spintronics"). A team of chemists and physicists from Columbia University discovered a strong relationship between electron transport and magnetism in chromium sulfide bromide, which was published in the journal Nature Materials on May 5, 2022. (CrSBr).

CrSBr is a so-called van der Waals crystal that can be peeled into stackable, 2D layers as thin as a few atoms in Chemist Xavier Roy's lab. CrSBr crystals are stable at ambient circumstances, unlike similar minerals that are swiftly destroyed by oxygen and water. These crystals also keep their magnetic characteristics at a relatively high temperature of -280F, eliminating the requirement for costly liquid helium chilled to -450F.

“CrSBr is infinitely easier to work with than other 2D magnets, which lets us fabricate novel devices and test their properties,” said Evan Telford, a postdoc in the Roy lab who graduated with a PhD in physics from Columbia in 2020. Researchers from the University of Washington's Nathan Wilson and Xiaodong Xu and Columbia's Xiaoyang Zhu discovered a relationship between magnetism and how CrSBr responds to light last year. Telford led the effort to investigate its electronic characteristics in the current study.

The researchers studied CrSBr layers using an electric field at various electron densities, magnetic fields, and temperatures—variable characteristics that can be altered to induce diverse effects in a material. CrSBr's magnetic altered as its electrical characteristics changed.

“Semiconductors have tunable electronic properties. Magnets have tunable spin configurations. In CrSBr, these two knobs are combined,” Roy explained. “That makes CrSBr attractive for both fundamental research and for potential spintronics application.”

According to Telford, magnetism is a difficult feature to measure directly, especially as the size of the material reduces, but measuring how electrons travel with a metric termed resistance is simple. Resistance in CrSBr can be used as a surrogate for magnetic states that are otherwise unobservable. “That’s very powerful,” Roy added, noting that researchers are working on circuits made of 2D magnets that might be utilized for quantum computing and storing vast quantities of data in a tiny space.

The relationship between the material's electronic and magnetic properties was caused by faults in the layers, which Telford described as "a lucky break." “People usually want the ‘cleanest’ material possible. Our crystals had defects, but without those, we wouldn’t have observed this coupling,” he explained.

To improve the ability to fine-tune the material's properties, the Roy lab is working with ways to create peelable van der Waals crystals with intentional flaws. They're also looking into whether different combinations of elements could work at higher temperatures while still preserving their useful qualities.

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