A New Dimension of Superconductivity

Kagome metals exhibit superconductivity through a unique wave-like distribution of electron pairs, a discovery that overturns previous assumptions and may lead to the development of novel superconducting components.

This groundbreaking research, driven by theoretical insights and enhanced by cutting-edge experimental techniques, marks a significant step towards realizing efficient quantum devices.

For about fifteen years, Kagome materials with their star-shaped structure reminiscent of a Japanese basketry pattern have captivated global research. Only staring from 2018 scientists have been able to synthesize metallic compounds featuring this structure in the lab. Thanks to their unique crystal geometry, Kagome metals combine distinctive electronic, magnetic, and superconducting properties, making them promising for future quantum technologies.

Professor Ronny Thomale of the Würzburg-Dresden Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter, and Chair of Theoretical Physics at the University of Würzburg (JMU) provided key insights in this class of materials with his early theoretical predictions. Recent findings published in Nature suggest these materials could lead to novel electronic components, such as superconducting diodes.

Breakthrough in Superconductivity

In a preprint online published on February 16, 2023, Professor Thomale’s team proposed that a unique type of superconductivity could manifest in Kagome metals, with Cooper pairs distributing in a wave-like fashion within the sublattices. Each “star point” contains a different number of Cooper pairs. Thomale’s theory has now been directly substantiated for the first time in an international experiment, causing a worldwide sensation. This overturns the earlier assumption that Kagome metals could only host uniformly distributed Cooper pairs.

Cooper pairs – named after physicist Leon Cooper – are formed at very low temperatures by pairs of electrons, and are essential for superconductivity. Acting collectively, they can create a quantum state, and can also move through a Kagome superconductor without resistance.

Quantum Phenomena and Research Progress

“Initially, our research on Kagome metals like potassium vanadium antimony (KV3Sb5) focused on the quantum effects of individual electrons, which, although not superconducting, can exhibit wave-like behavior in the material,” explains Thomale. “After experimentally confirming our initial theory on electron behavior with the detection of charge density waves two years ago, we tried to find additional quantum phenomena at ultralow temperatures. This led to the discovery of the Kagome superconductor. However, global physics research in Kagome materials is still in its infancy,” Thomale notes.

Transmitting Wave Motion

“Quantum physics is familiar with the pair-density wave phenomenon—a special form of a superconducting condensate. As we all know from cooking, when steam cools, it condenses and becomes liquid. Something similar happens in Kagome metals. At ultra-low temperatures around –193 degrees DOI: 10.1038/s41586-024-07798-y

“Spatially modulated superconductivity in the Kagome Hubbard model” by Tilman Schwemmer, Hendrik Hohmann, Matteo Dürrnagel, Janik Potten, Jacob Beyer, Stephan Rachel, Yi-Ming Wu, Srinivas Raghu, Tobias Müller, Werner Hanke, Ronny Thomale, 1 March 2024, Condensed Matter > Strongly Correlated Electrons.
arXiv:2302.08517

“Sublattice modulated superconductivity in the kagome Hubbard model” by Tilman Schwemmer, Hendrik Hohmann, Matteo Dürrnagel, Janik Potten, Jacob Beyer, Stephan Rachel, Yi-Ming Wu, Srinivas Raghu, Tobias Müller, Werner Hanke and Ronny Thomale, 1 July 2024, Physical Review B.
DOI: 10.1103/PhysRevB.110.024501