Researchers at the Hebrew University of Jerusalem have made a surprising discovery about how superconductivity behaves in extremely thin materials. Superconductors are materials that allow electric current to flow without resistance, which makes them incredibly valuable for technology. Usually, the properties of superconductors change predictably when the materials become thinner; however, this study found something unexpected.
The team, led by Ph.D. student Nofar Fridman under the guidance of Prof. Yonathan Anahory from the Racah Institute of Physics and the Nano Center at Hebrew University looked closely at thin films made from niobium diselenide (NbSe2), a special type of layered superconducting material, which can be assembled into structures where thickness is precisely controlled down to the few layer limit. By using advanced magnetic imaging techniques, the researchers measured how these materials respond to magnetic fields as their thickness decreased.
Breaking the Rules of Thickness
Typically, scientists expect the ability of a superconducting material to expel magnetic fields to become stronger as the material becomes thicker. Here, this length is gauged by a physical property called the Pearl length. This study confirmed that rule for samples thicker than ten atomic layers. However, when the films became extremely thin—just three to six layers (2-4 nm) —the researchers observed something unexpected: the Pearl length sharply increased and became thickness independent, breaking the expected pattern.
A Strange New Behavior Emerges
“Our findings reveal something completely unexpected that could be ubiquitous in superconducting materials,” explained Nofar Fridman, the Ph.D. student leading the study. “In very thin samples, superconductivity behaves differently from what we’ve known. It seems that below a certain thickness, superconductors host current mostly at their top and bottom surfaces, rather than throughout their volume. This finding opens up exciting new questions about superconductivity in ultra-thin materials.”
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