Science Gazette

Kagome metals confound science with their electron conspiracy in a Japanese lattice structure

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In search of a new kind of superconductivity: Scientists have found metals called kagome metals that have a crystal structure that resembles a traditional Japanese woven bamboo pattern. An international team of scientists has revealed that the underlying kagome lattice structure triggers the combined emergence of complicated quantum events, which might lead to an unusual sort of superconductivity.

A kagome pattern is formed by atoms

Three shifted regular triangular lattices make up a kagome design. The kagome lattice, as a consequence, is a regular pattern made up of David’s stars. Its name comes from the fact that it is a typical Japanese basket design. Materials crystallizing in a kagome lattice originally attracted interest in condensed matter physics in the early 1990s. Until 2018, when FeSn was discovered as the first kagome metal, correlated electronic states in kagome materials were thought to be generally insulating, which led to a heavy emphasis on magnetic problems. Ronny Thomale, a scientific member of the Würzburg-Dresden Cluster of Excellence ct.qmat — Complexity and Topology in Quantum Matter, suggested in 2012 that kagome metals might also produce exciting quantum phenomena.

“Kagome metals have sparked an enormous amount of scientific effort since their experimental discovery. The quest for kagome metals with unusual characteristics has started in all committed research organizations across the globe. One goal is to develop a new sort of superconductor, among other things “explains Thomale, who holds the Julius-Maximilians-Universität Würzburg (JMU) chair for theoretical condensed matter physics.

Surprising outcomes

In the field of kagome metals, a research team headed by the Paul Scherrer Institute (Schweiz) has made a novel finding. They observed the simultaneous development of multiple complex quantum phenomena in the compound KV3Sb5, culminating in a superconducting phase with broken time reversal symmetry.

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“There must be some unique new mechanism underlying every evidence of time reversal symmetry breaking in a non-magnetic substance,” Thomale argues. “Only a tiny percentage of known superconductors allow for the difference between travelling forward and backward in time. The very high temperature much above the superconducting transition point when the experimentally discovered evidence of time reversal symmetry breaking kicks in for KV3Sb5 is especially amazing. This stems from the electronic charge density wave, which is thought to be the superconductor’s parent state, where time-reversal symmetry may already be violated by orbital currents. The kagome lattice effects on the electrical density of states play an important role in their emergence. Forward and backward in time acquire a succinct identifiable meaning as soon as there are currents, i.e., the direction of time becomes significant. This is one of the main reasons for the community’s intense interest in kagome metals.”

The emergence of a new research area is expected

In 2020, a non-magnetic kagome metal with both charge density wave order and superconductivity was identified for the first time, after the discovery of magnetic Kagome metals in 2018. The discovery of broken time reversal symmetry in superconducting metals and above is a significant step forward for kagome metals. These discoveries, in particular, give experimental evidence that an unheard-of sort of unconventional superconductivity may be at work.

“The demonstration of this new sort of superconductivity in kagome metals will further drive the international quantum physics research boom,” says Matthias Vojta, the Dresden spokesman for the ct.qmat research alliance. “The Würzburg-Dresden Cluster of Excellence ct.qmat is one of the world’s premier quantum materials research facilities, and is well-equipped to study kagome metals using a variety of experimental and theoretical methods. Ronny Thomale, a member of our organization, has made pioneering contributions in this sector.”

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Professor Ronny Thomale (39) is one of the 25 founding members of the ct.qmat Cluster of Excellence and has held the JMU Chair for Theoretical Physics I since October 2016. In 2012, he established a hypothesis that is regarded the key foundation for understanding the new experimental findings on Kagome metals, in collaboration with Qianghua Wang’s research group at Nanjing University.

Outlook

The goal is that by showing time-reversal symmetry breaking, this novel principle of superconductivity, which might be discovered in kagome metals, can be applied to the technologically important domain of high temperature superconductors for dissipationless electrical transmission. The latest discovery in kagome metals will encourage researchers all around the globe to dig further into this new class of quantum materials. Despite the enthusiasm, direct measurement of orbital currents in kagome metals remains a technological challenge. If successful, this would be another another step toward a better understanding of how electrons interact on the kagome lattice to produce bizarre quantum events.

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