Electron conspiracy in a Japanese lattice pattern: Kagome metals baffle science

Date:
February 11, 2022
Source:
University of Wu"rzburg
Summary:
Toward a new kind of superconductivity: In the past four years
scientists have discovered metals whose crystal structure
mimics that of a traditional Japanese woven bamboo pattern:
kagome metals. The international research activity in this new
direction of quantum materials has recently reached a new climax:
an international team of physicists has discovered that the
underlying kagome lattice structure induces the joint appearance
of intricate quantum phenomena which can lead to an unprecedented
type of superconductivity.



FULL STORY ========================================================================== Toward a new kind of superconductivity: In the past four years
scientists have discovered metals whose crystal structure mimics that
of a traditional Japanese woven bamboo pattern: kagome metals. The international research activity in this new direction of quantum materials
has recently reached a new climax: an international team of physicists
has discovered that the underlying kagome lattice structure induces the
joint appearance of intricate quantum phenomena which can lead to an unprecedented type of superconductivity.


========================================================================== Atoms form a kagome pattern A kagome pattern is composed of three
shifted regular triangular lattices. As a result, the kagome lattice is
a regular pattern composed of stars of David. It is a common Japanese
basket pattern which is where its name derives from. In condensed matter physics, materials crystallizing in a kagome lattice have first gained significant attention in the early 90's. Until 2018, when FeSn as the
first kagome metal was found, correlated electronic states in kagome
materials had typically been conceived as being generically insulating,
and triggered a predominant research focus on magnetic frustrations. That kagome metals could likewise bring about fascinating quantum effects had already been predicted in 2012 by Ronny Thomale, scientific member of
the Wu"rzburg-Dresden Cluster of Excellence ct.qmat -- Complexity and
Topology in Quantum Matter.

"From the moment of their experimental discovery, kagome metals have
unleashed a tremendous amount of research activity. In all dedicated
research groups worldwide, the search has begun to look out for
kagome metals with exotic properties. Among other ambitions, one
hope is to realize a new type of superconductor," explains Thomale
who holds the chair for theoretical condensed matter physics at Julius-Maximilians-Universita"t Wu"rzburg, JMU.

Baffling results A research team led by the Paul Scherrer Institute
(Schweiz) has now achieved a new discoveryin kagome metals. In the
compound KV3Sb5, they observed the simultaneous appearance of several
intricate quantum phenomena, culminating in a superconducting phase with
broken time reversal symmetry.



========================================================================== "Whenever there is an indication of time reversal symmetry breaking in
a non- magnetic materialthere must be some exotic new mechanism behind
it," says Thomale. "Only a smallest fraction of known superconductors
would allow a distinction between moving 'forward' versus 'backward' in
time. What is particularly astounding is the comparably high temperature
far above the superconducting transition temperature at which the experimentally detected signature of time reversal symmetry breaking sets
in for KV3Sb5. This has its origin in the electronic charge density wave
as the supposed parent state of the superconductor where time-reversal
symmetry can already be broken through orbital currents. Their appearance
is intricately connected to the kagome lattice effects on the electronic density of states. As soon as there are currents, forward and backward in
time attain a concise distinguishable meaning, i.e., the direction of time becomes relevant. This is one central facet underlying the community's tremendous fascination for kagome metals." The anticipated rise of a new research domain After the discovery of magnetic Kagome metals in 2018,
a non-magnetic kagome metal featuring both, charge density wave order and superconductivity, was first discovered in 2020. The present observation
of broken time reversal symmetry within the superconducting phase and
above represents a new breakthrough for kagome metals. In particular,
these findings provide experimental evidence that an unprecedented type
of unconventional superconductivity could be at play.

"The demonstration of this new type of superconductivity in the kagome
metals will further fuel the worldwide research boom in quantum physics.," comments Matthias Vojta, the Dresden spokesperson of the research alliance ct.qmat. "The Wu"rzburg-Dresden Cluster of Excellence ct.qmat is one of
the leading quantum materials research centers worldwide and ideally
equipped to investigate kagome metals with a plethora of different
experimental and theoretical techniques. We are particularly proud
that our member Ronny Thomale has contributed groundbreaking work in
this field." Professor Ronny Thomale (39) has held the JMU Chair for Theoretical Physics I since October 2016 and is one of the 25 founding
members of the ct.qmat Cluster of Excellence. In 2012, he developed -- in parallel with the research group of Qianghua Wang of Nanjing University
-- a theory that is considered the crucial basis for understanding the
new experimental results on Kagome metals.

Outlook In demonstrating time-reversal symmetry breaking, the hope
is to take this new principle of superconductivity possibly found in
kagome metals and transcend it into the technologically interesting
realm of high temperature superconductors for dissipationless transport
of electricity. The recent discoveries in kagome metals will be an
incentive for researchers worldwide to take a closer look at this new
class of quantum materials. Despite all the excitement, the technically challenging direct measurement of orbital currents in kagome metals
is still lacking. If accomplished, this would constitute yet another
milestone towards a deeper understanding of the way electrons conspire
on the kagome lattice to give rise to exotic quantum phenomena.

========================================================================== Story Source: Materials provided by University_of_Wu"rzburg. Original
written by Katja Lesser. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. C. Mielke, D. Das, J.-X. Yin, H. Liu, R. Gupta, Y.-X. Jiang,
M. Medarde,
X. Wu, H. C. Lei, J. Chang, Pengcheng Dai, Q. Si, H. Miao,
R. Thomale, T.

Neupert, Y. Shi, R. Khasanov, M. Z. Hasan, H. Luetkens, Z. Guguchia.

Time-reversal symmetry-breaking charge order in a kagome
superconductor.

Nature, 2022; 602 (7896): 245 DOI: 10.1038/s41586-021-04327-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220211102649.htm

--- up 9 weeks, 6 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)