. 24/7 Space News .
ENERGY TECH
New insight into unconventional superconductivity
by Staff Writers
Villigen, Switzerland (SPX) Feb 10, 2022

Discovered time-reversal symmetry-breaking fields imply the presence of long-theorised 'orbital currents', where charge flows spontaneously in loops around the unit cells of the kagome lattice (artist's impression: Paul Scherrer Institute/ Mahir Dzambegovic)

The kagome pattern, a network of corner-sharing triangles, is well known amongst traditional Japanese basket weavers - and condensed matter physicists. The unusual geometry of metal atoms in the kagome lattice and resulting electron behaviour makes it a playground for probing weird and wonderful quantum phenomena that form the basis of next-generation device research.

A key example is unconventional - such as high-temperature - superconductivity, which does not follow the conventional laws of superconductivity. Most superconducting materials exhibit their seemingly magical property of zero resistance at a few degrees Kelvin: temperatures that are simply impractical for most applications. Materials that exhibit so-called 'high-temperature' superconductivity, at temperatures achievable with liquid nitrogen cooling (or even at room temperature), are a tantalising prospect.

Finding and synthesising new materials that exhibit unconventional superconductivity has become the condensed matter physicist's Holy Grail - but getting there involves a deeper understanding of exotic, topological electronic behaviour in materials.

An exotic type of electron transport behaviour that results in a spontaneous flow of charge in loops has long been debated as a precursor to high-temperature superconductivity and as a mechanism behind another mysterious phenomenon: the quantum anomalous Hall effect. This topological effect, the subject of F. Duncan M. Haldane's 2016 Nobel Prize winning work, occurs in certain two-dimensional electronic materials and relates to the generation of a current even in the absence of an applied magnetic field.

Understanding the quantum anomalous Hall effect is important not only for fundamental physics, but also for the potential applications in novel electronics and devices. Now, a PSI-led international collaboration has discovered strong evidence supporting this elusive electron transport behaviour.

Time-reversal symmetry-breaking charge ordering in the kagome superconductor KV3Sb5
The team, led by researchers from PSI's Laboratory for Muon Spin Spectroscopy, discovered weak internal magnetic fields indicative of an exotic charge ordering in a correlated kagome superconductor. These magnetic fields break so-called time-reversal symmetry, a type of symmetry that means that the laws of physics are the same whether you look at a system going forward or backward in time.

A natural explanation of the occurrence of time-reversal symmetry-breaking fields is a novel type of charge order. The charge ordering can be understood as a periodic modulation of the electron density through the lattice and rearrangement of the atoms into a higher-order (superlattice) structure.

The team focused their study on the kagome lattice, KV3Sb5, which superconducts below 2.5 Kelvin. Below a higher critical temperature of approximately 80 Kelvin, a giant quantum anomalous Hall effect is observed in the material, which was previously unexplained. The exotic charge ordering appears below this critical temperature of approximately 80 Kelvin, termed the 'charge ordering temperature'.

The discovered time-reversal symmetry-breaking fields implies an exotic type of charge order where currents move around the unit cells of the kagome lattice, known as orbital currents. These produce magnetism dominated by the extended orbital motion of the electrons in a lattice of atoms.

"Experimental realization of this phenomenon is exceptionally challenging, as materials exhibiting orbital currents are rare and the characteristic signals [of orbital currents] are often too weak to be detected," explains corresponding author, Zurab Guguchia, from the Lab of Muon Spin Spectroscopy at PSI, who led the team.

Although previous studies have shown the breaking of time-reversal symmetry below the superconducting temperature, this is the first example in which time-reversal symmetry is broken by charge order. This means that this putative exotic charge order classes as a new quantum phase of matter.

An extremely convincing piece of evidence
To search for the long disputed orbital currents, the physicists used highly sensitive muon spin rotation/relaxation spectroscopy (uSR) to detect the weak, tell-tale magnetic signals that they would generate.

Muons implanted into the sample serve as a local and highly sensitive magnetic probe to the internal field of the material, enabling magnetic fields as small as 0.001 uBohr to be detected. In the presence of an internal magnetic field, the muon spin depolarises. The muons decay into energetic positrons, which are emitted along the direction of the muon spin, carrying with them information on the muon spin polarisation in the local environment.

The researchers observed how, as the temperature is decreased to below 80K, the charge ordering temperature, a systematic shift in the magnetic signal appeared. Using the world's most advanced uSR facility at PSI, which enables application of fields up to 9.5 Tesla, the team could use an external high magnetic field to enhance the shift in the tiny internal magnetic fields and provide even stronger evidence that the magnetic field was due to internal orbital currents.

"We first performed the experiment with no external field," explains Dr. Guguchia, "and when we saw the systematic shift appear below the charge ordering temperature, we felt very motivated to continue. But when we then applied the high field and could promote this electronic response, we were delighted. It's a very, very convincing piece of evidence for something that has remained elusive for a long time."

A deeper understanding of unconventional superconductivity and the quantum anomalous Hall effect
The research provides arguably the strongest evidence yet that long debated orbital currents actually exist in the kagome material KV3Sb5. Theory suggests that the quantum anomalous Hall effect originates from orbital currents.

Therefore, orbital currents have been proposed in a number of unconventional superconductors that exhibit a strangely large quantum anomalous Hall effect; namely graphene, cuprates and kagome lattices, but actual evidence that they existed had been missing until now.

The discovery of time-reversal symmetry-breaking fields, which imply orbital currents - and the peculiar charge ordering that gives rise to them, opens doors to exotic avenues of physics and next-generation device research.

Orbital currents are considered to play a fundamental role in the mechanism of various unconventional transport phenomena including high-temperature superconductivity, with applications from power transmission to MAGLEV trains. The concept of orbital currents also forms the basis of orbitronics - an area that exploits the orbital degree of freedom as an information carrier in solid-state devices.

Research Report: "Time-reversal symmetry-breaking charge order in a correlated kagome superconductor"


Related Links
Paul Scherrer Institute
Powering The World in the 21st Century at Energy-Daily.com


Thanks for being there;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Monthly Supporter
$5+ Billed Monthly


paypal only
SpaceDaily Contributor
$5 Billed Once


credit card or paypal


ENERGY TECH
Superconductivity on the edge
Washington DC (SPX) Feb 04, 2022
Scientists recently discovered novel quantum materials whose charge carriers exhibit 'topological' features. Charge carriers are particles that transport electrical charges through a material. Topology is the study of the rules behind how shapes behave when they change. For example, a doughnut shape will still have a hole if it changes continuously from round to square or if it is twisted or stretched. Unless we do something drastic, like cutting or tearing, the doughnut cannot be changed into ano ... read more

Comment using your Disqus, Facebook, Google or Twitter login.



Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

ENERGY TECH
Global patent filings surged to record high in 2021: UN

China joins industrial design IP treaty

Northrop Grumman's 17th Resupply Mission packed with science and technology for ISS

Astronaut hits 300 days in space, on way to break NASA record

ENERGY TECH
Rocket Lab brings forward launch for earth imaging company Synspective

Musk 'confident' of Starship orbital launch this year

SpaceX Starship orbital flight likely this year

Astra Space stock plunges after rocket failure during NASA launch

ENERGY TECH
Sols 3383-3384: Picking Our Way to the Pediment

How easy is it to turn water into oxygen on Mars

Predicting the efficiency of oxygen-evolving electrolysis on the Moon and Mars

Sols 3381-3382: Whence We Came

ENERGY TECH
China welcomes cooperation on space endeavors

China Focus: China to explore lunar polar regions, mulling human landing: white paper

China to boost satellite services, space technology application: white paper

China Focus: China to explore space science more: white paper

ENERGY TECH
Russian Soyuz rocket launches 34 new UK satellites

Protecting dark and quiet skies from satellite constellation interference

Solar storm knocks out 40 SpaceX Starlink satellites

Sidus Space announces deal with Red Canyon Software to support LizzieSat Constellation

ENERGY TECH
Coca-Cola says 25% of packaging will be reusable by 2030

A new way to shape a material's atomic structure with ultrafast laser light

Brazil launches plan to expand mining in Amazon

Rare earth elements await in waste

ENERGY TECH
Planetary bodies observed in habitable zone of dead star

Giant sponge gardens discovered on seamounts in the Arctic deep sea

Animal genomes: Chromosomes almost unchanged for over 600 million years

Puffy planets lose atmospheres, become Super Earths

ENERGY TECH
NASA Telescope Spots Highest-Energy Light Ever Detected From Jupiter

Juno and Hubble data reveal electromagnetic 'tug-of-war' lights up Jupiter's upper atmosphere

Oxygen ions in Jupiter's innermost radiation belts

Ocean Physics Explain Cyclones on Jupiter









The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.