- Press Release Distribution

Princeton-led team discovers unexpected quantum behavior in kagome lattice

Experiments suggest evidence for novel patterns of electronic charge distribution in a kagome material whose handedness can be manipulated with a magnetic field

( An international team led by researchers at Princeton University has uncovered a new pattern of ordering of electric charge in a novel superconducting material.

The researchers discovered the new type of ordering in a material containing atoms arranged in a peculiar structure known as a kagome lattice. While researchers already understand how the electron's spin can produce magnetism, these new results provide insights into the fundamental understanding of another type of quantum order, namely, orbital magnetism, which addresses whether the charge can spontaneously flow in a loop and produce magnetism dominated by extended orbital motion of electrons in a lattice of atoms. Such orbital currents can produce unusual quantum effects such as anomalous Hall effects and be a precursor to unconventional superconductivity at relatively high temperatures. The study was published in the journal Nature Materials.

"The discovery of a novel charge order in a kagome superconductor with topological band-structure which is also tuneable via a magnetic field is a major step forward that could unlock new horizons in controlling and harnessing quantum topology and superconductivity for future fundamental physics and next-generation device research," said M. Zahid Hasan, the Eugene Higgins Professor of Physics at Princeton University, who led the research team.

The discovery's roots lie in the workings of two fundamental discoveries in the 1980's. One is the quantum Hall effect - a topological effect which has been the subject of decades-long research. The Hall effect was the first example of how a branch of theoretical mathematics, called topology, could fundamentally change how to describe and classify the matter that makes up the world. Important theoretical concepts on the quantized Hall effect were put forward in 1988 by F. Duncan Haldane, the Thomas D. Jones Professor of Mathematical Physics and the Sherman Fairchild University Professor of Physics, who in 2016 was awarded the Nobel Prize.

The second precedent was the discovery of the unconventional high-temperature superconductor which was the subject of the Nobel Prize in 1987. The unusual state of these superconductors has puzzled scientists. Important theoretical concepts on loop currents as a precursor of unconventional superconductivity were put forward in late 1990s by several theorists. In both cases, the key proposal is that the charge can flow in a special lattice to produce effects like orbital magnetism. However, direct experimental realization of such a highly speculative type of electronic quantum charge order is extremely challenging.

"The realization of orbital current type charge order would require the materials to have both strong interactions and special lattice geometries that were realized only the last few years," said Hasan.

Through several years of intense research on several geometrical lattice systems (Nature 562, 91 (2018); Nature Phys 15, 443 (2019), Phys. Rev. Lett. 123, 196604 (2019), Nature Commun. 11, 559 (2020), Phys. Rev. Lett. 125, 046401 (2020), Nature 583, 533 (2020), Nature Reviews Physics 3, 249 (2021), the team gradually realized that kagome superconductors can host such topological-type charge order. Dozens of superconductors with kagome lattices have been discovered over the last 40 years but none showed the desired pattern. One notable kagome superconductor is AV3Sb5 (A=K,Rb,Cs), which early experiments have shown to contain hints of a hidden order around 80 degrees Kelvin, making it a plausible platform for looking for the topological-type charge order.

"Superconductivity often suggests instabilities for the charge of the system, and the kagome lattice is known to be a frustrated lattice system," Hasan said. "The kagome superconductors can form various exotic charge orders, including the topological-type charge order related to their global band-structure. That led us to our search in this family, although it was not clear whether this superconductivity was unconventional when we started to work on this material."

The Princeton team of researchers used an advanced technique known as sub-atomic-resolution scanning tunneling microscopy, which is capable of probing the electronic and spin wavefunctions of material at the sub-atomic scale with sub-millivolt energy resolution at sub-Kelvin temperatures. Under these fine-tuned conditions, the researchers discovered a novel type of charge order that exhibits chirality - that is, orientation in a particular direction - in AV3Sb5.

"The first surprise was that the atoms of the material rearrange themselves into a higher-order (superlattice) lattice structure that was not expected to be there in our data," said Yuxiao Jiang, a graduate student at Princeton and one of the first co-authors of the paper. "Such a superlattice has never been seen in any other kagome system known to us."

The superlattice was the first hint to the researchers that there could be something unconventional in this material. The researchers further increased the temperature of the material to find that the superlattice disappeared above the critical temperature of the hidden phase estimated from the electrical transport behavior of the bulk of the material.

"This consistency gives us the confidence that what we observed is more likely to be a bulk ordering phenomenon rather than a surface effect," said Jia-Xin Yin, an associate research scholar and another co-first author of the study.

Hasan added, "For a bulk charge order, we need to examine further whether there is an energy gap and whether the charge distribution in the real space shows any reversal across the energy gap."

The researchers soon checked both points to confirm again that the unexpected charge order shows a striking charge reversal across the energy gap, which also disappears at the same critical temperature. The accumulated experimental evidence established that the researchers observed a charge order in a kagome material, which has never been reported in any other kagome system.

"Now we are in a position to ask the bigger question: whether it can be a topological charge order?" said Hasan.

Yin added, "Luckily, through our systematic research of geometrical lattice systems over recent years, we have developed a vector magnetic field-based scanning tunneling microscopy methodology to explore any potential topological feature of the material."

Fundamentally, the magnetic field applied on an electronic system leads to a nontrivial topology: the magnetic flux quantum (h/e) and quantum Hall conductance (Ne2/h, related to Chern number N, a topological invariant) are governed by the same set of fundamental constants, including the Planck's constant h and elemental charge e; the vector nature of the field can differentially interact with the chirality of topological matter to provide access to effects related to the topological invariant.

The researchers performed experiments on the charge order at zero magnetic field, a positive magnetic field, and a negative magnetic field. "Before the data was taken, we really didn't know what would happen," Hasan said.

Once the experiments were complete, Jiang said, the answer to the question of topological-like charge order was "yes."

"We found that the charge order actually exhibits a detectable chirality, which can be switched by the magnetic field," Jiang said.

The researchers are excited about their initial discovery. "Before the claim could be made, we still needed to reproduce this result multiple times, to rule out effects from the scanning probe, which may be extrinsic in nature," said Yin.

The researchers further spent several months to find that this magnetic field-switchable chiral charge order is ubiquitous in KV3Sb5, RbV3Sb5 and CsV3Sb5. "Now we are convinced that it is an intrinsic property of this class of material," Hasan added, "And that's very exciting!"

The magnetic field explicitly breaks time-reversal symmetry. Therefore, their observation shows that the chiral charge order in the kagome lattice breaks time-reversal symmetry. This is somewhat analogous with the Haldane model in the honeycomb lattice or the Chandra Varma model in the CuO2 lattice.

Researchers further identified the direct topological consequence of such chiral charge order. With the help of first-principle calculations of the band structure, the team found that this chiral charge order will produce a large anomalous Hall effect with orbital magnetism, which is consistent with the existing transport result which was interpreted differently in a previous work.

Now the theoretical and experimental focus of the group is shifting to the dozens of compounds with kagome lattice flatband properties and also superconductivity. "This is like discovering water in an exoplanet - it opens up a new frontier of topological quantum matter research our laboratory at Princeton has been optimized for," Hasan said.


The research included contributions from scientists at Princeton University, the University of Zurich, the University of California-Santa Barbara, Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, the Paul Scherrer Institute, Cornell University, Nanyang Technological University, Boston College, Julius Maximilians University of Wurtzburg, Lawrence Berkeley National Laboratory, and Oak Ridge National Laboratory.

In addition to Yu-Xiao Jiang and Jia-Xin Yin, equal contributions were made by Nana Shumiya of Princeton, M. Michael Denner of University of Zurich, Brenden R. Ortiz of the University of California-Santa Barbara, and Gang Xu of Huazhong University of Science and Technology.

The study, "Unconventional chiral charge order in kagome superconductor KV3Sb5," was published in the journal Nature Materials on June 11, 2021. DOI:

Experimental and theoretical work at Princeton University was supported by the Gordon and Betty Moore Foundation and sample characterization was supported by the U. S. Department of Energy. Support was also received from National Science Foundation, the California NanoSystems Institute, the German Research Foundation, and the European Union's Horizon 2020 research and innovation program.


Overcoming a newly recognized form of resistance to modern prostate cancer drugs

Overcoming a newly recognized form of resistance to modern prostate cancer drugs
Cancer cells have an uncanny ability to evolve and adapt to overcome the treatments used against them. While patient survival has been extended by modern drugs that block the production or action of male hormones that fuel prostate cancer -- androgen receptor inhibitors such as enzalutamide, apalutamide, darolutamide, and abiraterone -- eventually these drugs stop working. At that point, a patient's disease is considered incurable, or what doctors call metastatic, castration-resistant prostate cancer. In a new study, a team of researchers led by Joshi Alumkal, M.D., who ...

Will reduction in tau protein protect against Parkinson's and Lewy body dementias?

Will reduction in tau protein protect against Parkinsons and Lewy body dementias?
BIRMINGHAM, Ala. - Will a reduction in tau protein in brain neurons protect against Parkinson's disease and Lewy body dementias? A new study, published in the journal eNeuro, suggests the answer is no. If this is borne out, that result differs from Alzheimer's disease, where reducing endogenous tau levels in brain neurons is protective for multiple models of the disease -- which further suggests that the role of tau in the pathogenesis of Lewy body dementias is distinct from Alzheimer's disease. Both Parkinson's disease dementia and Lewy body dementia are characterized by intracellular aggregates of misfolded alpha-synuclein protein in brain neurons, and the two diseases together are the second most common cause of neurodegenerative dementia after ...

The end of Darwin's nightmare at Lake Victoria?

Lake Victoria, which came under the spotlight in 2004 by the documentary "Darwin's nightmare", is not only suffering from the introduction and commercialisation of the Nile perch. A study lead researchers from the University of Liège (Belgium) has highlighted other worrying phenomena, particularly climatic ones, which have an equally important impact on the quality of the lake's waters. Located in East Africa, just south of the Equator, Lake Victoria is the source of the Nile and is the largest tropical lake in the world. With a surface area of 68,800 km² (twice the size of Belgium), it is considered to be one of the largest water and fishery resources in East Africa, supporting more than 47 million people in the three neighbor countries ...

Study: Men doing more family caregiving could lower their risk of suicide

Colorado State University Professor of Psychology Silvia Sara Canetto has spent many years researching patterns and meanings of suicide by culture, trying to make sense of the variability in women's and men's suicide mortality around the world. Suicide rates are generally higher in men than in women, but not everywhere - which suggests cultural influences. Canetto and colleagues have completed a new study that provides insight into what may contribute to men's suicide vulnerability. The study tests Canetto's theory that men's suicide mortality ...

Researchers dig deeper into how cells transport their waste for recycling

Researchers dig deeper into how cells transport their waste for recycling
Scientists at Sanford Burnham Prebys have gained a deeper insight into the intricacies of autophagy, the process in which cells degrade and recycle cellular components. The findings, published in Current Biology, describe how the "trash bags" in a cell--called autophagosomes--are tagged to direct their movement to the cellular "recycling plants" where waste is processed. The research opens new paths to understanding the relationship between autophagy and age-related diseases such as cancer and neurological disorders. "Our latest study identifies how a chemical modification (phosphate-related ...

Organic farming could feed Europe by 2050

Organic farming could feed Europe by 2050
Food has become one of the major challenges of the 21st century. According to a study carried out by CNRS scientists1, an organic, sustainable, biodiversity-friendly agro-food system, could be implemented in Europe and would allow a balanced coexistence between agriculture and the environment. The scenario proposed is based on three levers. The first would involve a change in diet, with less consumption of animal products, making it possible to limit intensive livestock farming and eliminate feed imports. The second lever would require the application of the principles of agroecology, with the generalization of long, diversified crop rotation systems2 incorporating nitrogen-fixing legumes, making it possible to do without synthetic nitrogen fertilizers and ...

Assessing Racial, Ethnic disparities in access to COVID-19 vaccination sites

What The Study Did: Researchers reviewed access to COVID-19 vaccination sites in Brooklyn, the most populated borough in New York, to better understand disparities in vaccination. Authors: Natasha Williams, Ed.D., M.P.H., of the New York University Grossman School of Medicine in New York, is the corresponding author. To access the embargoed study: Visit our For The Media website at this link (doi:10.1001/jamanetworkopen.2021.13937) Editor's Note: The article includes funding/support disclosures. Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support. INFORMATION: Media advisory: The ...

COVID-19 in Spain

What The Study Did: Researchers describe the local transmission pattern of SARS-CoV-2 in Valencia, the third most populated city in Spain. Authors: Carolina Romero García, M.D., Ph.D., of the University General Hospital, European University, in Valencia, Spain, is the corresponding author. To access the embargoed study: Visit our For The Media website at this link (doi:10.1001/jamanetworkopen.2021.13818) Editor's Note: The article includes conflict of interest and funding/support disclosures. Please see ...

Pregnancy outcomes are affected by both maternal and paternal inflammatory disease

Karin Hellgren and colleagues examined pregnancy outcomes in relation to disease activity and antirheumatic treatment strategies in women with RA. This matched cohort study from Sweden and Denmark explored the associations between maternal RA and pre-term birth (PTB), or delivering babies small for gestational age (SGA)in relation to the mother's disease activity and use of antirheumatic treatment before and during pregnancy. Using national medical birth registers and rheumatology registers, the authors looked at1739pregnancies in women with RA, and 17,390 control pregnancies in the general population. Overall, women with RA had an increased likelihood of having pre-term and small babies. High ...

Passive smoking and air pollution -- links to arthritis development and poor response to therapy

RA is an inflammatory autoimmune disease that causes pain, swelling and stiffness in the joints. It can also cause fatigue, and the underlying inflammation may affect other body systems. It is more common in women than in men. To date, active smoking has been the most reproducibly reported risk factor for a type of RA called anti-citrullinated protein antibody (ACPA) positive RA-particularly in people who carry the HLA-DRB1-shared epitope alleles. Nguyen and colleagues set out to investigate the relationship between passive smoking and the risk of developing RA in a large prospective cohort of healthy French women. The E3N-EPIC (Etude Epidémiologique au prèsdes femmes de la Mutuelle générale de l'Education ...


Scientists model 'true prevalence' of COVID-19 throughout pandemic

New breakthrough to help immune systems in the fight against cancer

Through the thin-film glass, researchers spot a new liquid phase

Administering opioids to pregnant mice alters behavior and gene expression in offspring

Brain's 'memory center' needed to recognize image sequences but not single sights

Safety of second dose of mRNA COVID-19 vaccines after first-dose allergic reactions

Changes in disparities in access to care, health after Medicare eligibility

Use of high-risk medications among lonely older adults

65+ and lonely? Don't talk to your doctor about another prescription

Exosome formulation developed to deliver antibodies for choroidal neovascularization therapy

Second COVID-19 mRNA vaccine dose found safe following allergic reactions to first dose

Plant root-associated bacteria preferentially colonize their native host-plant roots

Rare inherited variants in previously unsuspected genes may confer significant risk for autism

International experts call for a unified public health response to NAFLD and NASH epidemic

International collaboration of scientists rewrite the rulebook of flowering plant genetics

Improving air quality reduces dementia risk, multiple studies suggest

Misplaced trust: When trust in science fosters pseudoscience

Two types of blood pressure meds prevent heart events equally, but side effects differ

New statement provides path to include ethnicity, ancestry, race in genomic research

Among effective antihypertensive drugs, less popular choice is slightly safer

Juicy past of favorite Okinawan fruit revealed

Anticipate a resurgence of respiratory viruses in young children

Anxiety, depression, burnout rising as college students prepare to return to campus

Goal-setting and positive parent-child relationships reduce risk of youth vaping

New research identifies cancer types with little survival improvements in adolescents and young adul

Oncotarget: Replication-stress sensitivity in breast cancer cells

Oncotarget: TERT and its binding protein: overexpression of GABPA/B in gliomas

Development of a novel technology to check body temperature with smartphone camera

The mechanics of puncture finally explained

Extreme heat, dry summers main cause of tree death in Colorado's subalpine forests

[] Princeton-led team discovers unexpected quantum behavior in kagome lattice
Experiments suggest evidence for novel patterns of electronic charge distribution in a kagome material whose handedness can be manipulated with a magnetic field