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Metal Kagome boggle the flag

Metal Kagome boggle the flag

Towards a new type of superconductivity: Over the past four years, scientists have discovered minerals whose crystal structure mimics that of a traditional Japanese woven bamboo pattern: Kagome minerals. International research activity in this new direction of quantum materials has recently reached a new high point: an international team of physicists has discovered that the fundamental structure of the Kagome lattice stimulates the co-emergence of complex quantum phenomena that can lead to an unprecedented type of superconductivity.

The atoms form a kagome pattern

The kagome pattern consists of three overlapping regular triangular grids. As a result, the kagome grid is a regular pattern made up of Stars of David. This is a popular Japanese basket pattern, hence its name. In condensed matter physics, amorphous materials in the Kagome lattice first attracted attention in the early 1990s. Until 2018, when FeSn was discovered as the first Kagome metal, the associated electronic states in Kagome materials were generally designed to be generally insulators and the mainstream research fueled magnetic frustrations. The fact that kagome metals can also cause fascinating quantum effects was already predicted in 2012 by Ronny Thomale, scientific member of the Würzburg-Dresden Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter.

“From the moment of their experimental discovery, Kagome minerals have unleashed a tremendous amount of research activity. In all the specialized research groups around the world, research has begun to search for Kagome minerals with peculiar properties. Among other ambitions, one hope is to realize a new type of conductor superfluidity,” says Tomal, head of theoretical condensed matter physics at Julius-Maximilians-Universität Würzburg, JMU.

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worrying results

A research team led by the Paul Scherrer Institute (Switzerland) made a new discovery in the Kagome minerals. In the KV3Sb5 complex, they observed the simultaneous emergence of several complex quantum phenomena, resulting in a superconducting phase with discontinuous time-reversal symmetry.

“When there is an indication of a time-reversal symmetry breaking in a non-magnetic material, there must be a strange new mechanism behind it,” says Thomale. “Only a small fraction of known superconductors can distinguish between moving ‘forward’ and ‘backward’ in time. What is particularly surprising is the relatively high temperature above the superconducting transition temperature at which the experimental signature of the time-reversal symmetry is detected in KV3swear5. This has its origin in the electron charge density wave as a putative origin state of the superconductor where the time-reversal symmetry can indeed be broken by orbital currents. Their appearance is closely related to the effects of the lattice kagome on the electron density of states. As soon as there are currents, forward and backward in time takes on a brief and distinct meaning, i.e. the direction of time becomes appropriate. This is the central aspect behind society’s massive fascination with Kagome minerals. »

The expected rise of a new field of research

After the discovery of magnetic Kagome minerals in 2018, a non-magnetic Kagome metal exhibiting both charge density wave order and superconductivity was first discovered in 2020. The current observation of the broken time-reversal symmetry in the superconducting phase and above represents a new breakthrough. for Kagome Minerals. In particular, these results provide experimental evidence for an unprecedented type of unconventional superconductivity.

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“Demonstration of this new type of superconductivity in Kagome minerals will fuel a global quantum physics research boom,” comments Matthias Voeta, Dresden spokesperson for the ct.qmat research alliance. “The Würzburg-Dresden ct.qmat Group of Excellence is one of the world’s leading quantum materials research centers and is ideally equipped to study kagome metals with a large number of different experimental and theoretical techniques. We are particularly proud that our member Ronny Thomale has contributed work in this field. »

Professor Ronnie Tomal (39 years old) has held the JMU Chair in Theoretical Physics 1 since October 2016 and is one of the 25 founding members of the ct.qmat Center of Excellence. In 2012, he developed – in parallel with Qianghua Wang’s research group from Nanjing University – a theory that is the critical basis for understanding new experimental findings on Kagome minerals.


By demonstrating temporal reversal symmetry breaking, the hope is that we can take this new principle of superconductivity that may exist in Kagome minerals and move beyond it into the technically interesting field of high-temperature superconductors for non-dispersion heat transfer. Recent discoveries in Kagome minerals will inspire researchers around the world to take a closer look at this new class of quantum materials. Despite all this excitement, a technically difficult direct measurement of orbital currents in Kagome minerals still does not exist. If accomplished, it would be another step toward a deeper understanding of how electrons on the kagome lattice conspire to give rise to strange quantum phenomena.

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Material offered by University of Würzburg. Original by Katja Lesser. Note: Content can be modified according to style and length.