Researchers at the Hebrew University of Jerusalem, led by Ph.D. student Nofar Fridman and Prof. Yonathan Anahory, have discovered unexpected behavior in superconductivity within extremely thin materials. Superconductors, which allow electric current to flow without resistance, typically exhibit predictable changes when thinned. However, the team found surprising results when studying thin films of niobium diselenide (NbSe2), a layered superconducting material. Using advanced magnetic imaging techniques, they measured the material’s response to magnetic fields as its thickness decreased, revealing new insights into superconductivity at the nanoscale.
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.
“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.”
The team’s supervisor, Prof. Yonathan Anahory, emphasized the importance of their method, saying, “Our high-resolution magnetic imaging allowed us to see details that previous methods couldn’t detect. By finding this unique surface superconductivity, we’ve expanded our understanding of how superconducting materials behave at extremely small scales. This could have significant implications for future research and technologies.”
This discovery sheds new light on superconductivity in very thin films and challenges previously held theories. It also highlights how specialized measurement techniques can uncover surprising new physical phenomena, potentially opening avenues for innovative applications in quantum technology.
For more information: Nature Communications
Image: A schematic illustration of the experimental setup shows a scanning magnetic microscope positioned above two different samples. One sample exhibits only surface superconductivity, while the other displays conventional superconductivity.
