It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Monday, April 15, 2024
WHITE SUPREMACY KILLS
‘Deaths of despair’ among Black Americans surpassed those of white Americans in 2022
UCLA Health analysis also found that Native Americans had highest combined death rate from suicide, alcohol use and drug overdose from 1999 through 2022
UNIVERSITY OF CALIFORNIA - LOS ANGELES HEALTH SCIENCES
A new analysis by researchers at UCLA Health found that mortality rates of middle-aged Black Americans caused by the “deaths of despair” -- suicide, drug overdose and alcoholic liver disease – surpassed the rate of white Americans in 2022. Native Americans also had more than double the rate of both Black and white Americans that year.
The results of the research, published in the journal JAMA Psychiatry, are the latest from UCLA Health to counter a nearly decade-old narrative that “deaths of despair” have primarily impacted white Americans.
The “deaths of despair” theory rose to prominence following a 2015 study that analyzed rising mid-life mortality, and decreasing life expectancy, in the U.S from 1999 to 2013.
The study became a focus of ongoing national discourse after it found white Americans had the highest mortality rates from these causes at 72.15 per 100,000 people in 2013, which was two times that of Black Americans. The findings sparked a narrative that the rising death rates were primarily impacting less educated white Americans who were experiencing a perceived loss of economic and social status.
However, data for Native Americans were not included in the 2015 study or in the many follow-up analyses it triggered. A 2023 study by UCLA Health determined that Native Americans have had a considerably higher midlife death rate from deaths of despair compared to white Americans for all available years of data 1999-2021.
In the new data analysis, UCLA Health researchers used publicly available records from the U.S. Centers for disease control to determine rates of deaths of despair through 2022 for white, Black and Native Americans ages 45-54.
The analysis found:
The rate of deaths of despair among Black Americans (103.81 per 100,000 people) surpassed that of white Americans (102.63 per 100,000) in 2022.
The rate among Black Americans tripled from 2013-2022 from 36.24 per 100,000 to 103.81 per 100,000 people, with 2015 onward marking a sharp increase in deaths.
The rate for Native American and Alaska Native populations was the highest at 241.7 per 100,000 people in 2022.
The rate of deaths of despair for Native American/Alaska Native populations has remained significantly higher than white Americans from 1999 to 2022.
Native American/Alaska Native had the highest mortality rates from suicide, alcoholic liver disease and drug overdose compared to Black and white Americans.
Deaths of despair in white Americans increased from 72.15 per 100,000 people in 2013 to 102.63 per 100,000 people in 2022.
Study coauthor Joseph Friedman, PhD, MPH, of the David Geffen School of Medicine at UCLA, said the results highlight the sharply rising rates of premature mortality related to mental health issues and substance use disorders with large racial and ethnic inequalities.
“The findings reinforce the notion that we need to invest in services that can address these issues and, ultimately, we need much more comprehensive access to low-barrier mental health care and substance use treatment in the U.S.,” Friedman said. “And we need to specifically make sure those treatments, services and programs are implemented in a way that is accessible for communities of color and will actively work to address inequality.”
The data does not identify the circumstances behind these deaths, but Friedman said the increasing rates of deaths of despair largely relate to mental health and substance use disorders. Black Americans have been disproportionately affected by the drug overdose crisis. Other factors include differential access to health care and social services; an increasingly toxic illicit drug supply, namely fentanyl; and worsening economic insecurity.
Article: Trends in Deaths of Despair by Race and Ethnicity From 1999 to 2022. Published Online: April 10, 2024. doi:10.1001/jamapsychiatry.2024.0303
Trends in Deaths of Despair by Race and Ethnicity From 1999 to 2022
ARTICLE PUBLICATION DATE
10-Apr-2024
JAMA NETWORK
Trends in deaths of despair by race and ethnicity
JAMA Psychiatry
About The Study: As of 2022, the midlife mortality rates from deaths of despair (deaths from suicide, drug overdose, and alcoholic liver disease) among Black individuals were higher than rates among white individuals, and rates among American Indian or Alaska Native individuals remained higher than rates in the other groups. Rising inequalities in deaths of despair among American Indian or Alaska Native and Black individuals were largely attributable to disproportionate early mortality from drug- and alcohol-related causes, which increased leading up to and during the COVID-19 pandemic.
Authors: Joseph Friedman, Ph.D., M.P.H., of the University of California, Los Angeles, is the corresponding author.
Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support.
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Race, ethnicity, and delayed time to COVID-19 testing among health care workers
JAMA NETWORK
About The Study: In this cross-sectional study of health care personnel (HCP), compared with non-Hispanic white HCP and clinical HCP with graduate degrees, non-Hispanic Black HCP, non-Hispanic HCP of other races, and HCP of all other professional and education backgrounds were more likely to have delayed COVID-19 testing. These findings suggest that time to testing may serve as a valuable metric in evaluating sociodemographic disparities in the response to COVID-19 and future health mitigation strategies.
Authors: DaMarcus E. Baymon, M.D., of Brigham and Women’s Hospital in Boston, is the corresponding author.
Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support.
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About JAMA Network Open: JAMA Network Open is an online-only open access general medical journal from the JAMA Network. On weekdays, the journal publishes peer-reviewed clinical research and commentary in more than 40 medical and health subject areas. Every article is free online from the day of publication.
JOURNAL
JAMA Network Open
Living near green space associated with fewer emotional problems in preschool-age kids, NIH study finds
Children who live in areas with natural spaces (e.g., forests, parks, backyards) from birth may experience fewer emotional issues between the ages of 2 and 5, according to a study funded by the NIH Environmental Influences on Child Health Outcomes (ECHO) program.
While research has suggested that time in nature is important for mental health, studies examining the effects on young children are limited. ECHO investigators addressed this research gap by analyzing information from parents about the behavior of their children from ages 2 to 11. They combined this data with the family’s residential address when the child was born and satellite data on live vegetation density around their homes.
What researchers found in their analysis, published in JAMA Network Open, was that higher levels of green spaces up to three-fourths of a mile from a child’s home were linked with lower anxiety and depression symptoms from ages 2 to 5 years. The association persisted even after researchers factored in the child’s sex, parent education, age at birth, and neighborhood socioeconomic vulnerability. Researchers did not find a significant association between green space around the home and mental health symptoms in later childhood years from ages 6 to 11, when children spend more time at school.
“Our research supports existing evidence that being in nature is good for kids,” said Nissa Towe-Goodman, PhD, an ECHO researcher from the Frank Porter Graham Child Development Institute at the University of North Carolina, Chapel Hill. “It also suggests that the early childhood years are a crucial time for exposure to green spaces.”
Most research so far has been limited to studying one or a few cities at a time, and focused on adult health. Because the ECHO Program collects data nationwide, researchers were able to examine data from children in 199 counties across 41 U.S. states, exploring the connection between exposure to green spaces from birth and anxiety, depression, aggression, and other symptoms during early or middle childhood.
The study included children born between 2007 and 2013 and whose parents completed the Child Behavior Checklist, a common survey to rate a child’s emotional and behavioral symptoms. The 2,103 children included in the study ranged in age from 2 to 11, spanning early and middle childhood.
Green space exposure was measured using the Normalized Difference Vegetation Index (NDVI), a widely used metric for quantifying vegetation density using sensor data. NDVI values range from -1 to 1. High NDVI values (approximately 0.6 to 0.9) represent dense vegetation, such as forests; values close to zero represent areas without live vegetation.
“In the future, researchers could look into what kinds of experiences in nature are connected to kids' early mental health,” said Dr. Towe-Goodman. “Also, we should study how creating or preserving natural areas around homes and schools might make a difference in a child’s mental health.”
Dr. Towe-Goodman lead this collaborative research in JAMA Network Open.
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About ECHO:
Launched in 2016, the Environmental influences on Child Health Outcomes (ECHO) Program is a research program in the Office of the Director at the NIH with the mission to enhance the health of children for generations to come. ECHO investigators study the effects of a broad range of early environmental influences on child health and development. For more information, visit echochildren.org.
About the NIH: NIH, the nation’s medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information, visit www.nih.gov.
JOURNAL
JAMA Network Open
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
People
ARTICLE TITLE
Children who live in areas with natural spaces (e.g., forests, parks, backyards) from birth may experience fewer emotional issues between the ages of 2 and 5, according to a study funded by the NIH Environmental Influences on Child Health Outcomes (ECHO) program. While research has suggested that time in nature is important for mental health, studies examining the effects on young children are limited. ECHO investigators addressed this research gap by analyzing information from parents about th
ARTICLE PUBLICATION DATE
10-Apr-2024
Preschoolers in front of the screen: let's turn it off so they can connect!
Preschoolers who use mobile devices more frequently have lower quality and quantity of parent-child interaction than their peers who do not use them
EÖTVÖS LORÁND UNIVERSITY
Preschoolers who use mobile devices more frequently have lower quality and quantity of parent-child interaction than their peers who do not use them. Researchers from the Alpha Generation Lab at the Department of Ethology, ELTE Eötvös Loránd University, hypothesized that mobile phone use takes time away from and interferes with social activities, thereby degrading the quality of time spent together, according to their article published in the journal Frontiers in Child and Adolescent Psychiatry.
"A total of 72 parent-child pairs took part in our research. The parents reported on the family's device use habits and time spent together in a questionnaire, but their interaction with and behaviour toward their children was also observed in a laboratory study," shared Dr. Krisztina Liszkai-Peres, the lab's researcher and first author of the study.
The researchers included 47 mobile-using preschoolers in the study: they considered a child as a mobile user if they had been using the device for at least 6 months and spent at least 2 hours per week using it actively such as playing games. The non-user group included 25 children who, according to their parents, had actively used a mobile phone or tablet only up to 5 times in their lifetime (passive screen time, e.g. watching videos, was not an exclusion criterion).
"For the survey, we developed a 31-item parent questionnaire to assess parents' and children's digital media use habits, children's problematic mobile use, and the family’s shared digital and non-digital (real-life) leisure activities. In the laboratory, we measured the quality of parent-child interaction in two different situations: in a 5-minute long free play session, during which the child-parent pairs were free to play with any of the games provided, and a 5-minute long structured play session," explained Dr. Veronika Konok, research fellow at the Department of Ethology and lead researcher of the Alpha Generation Lab.
In the structured game, the parent-child pair had to draw using the classic drawing board (etch-a-sketch), where one knob should be turned to draw vertically and the other to draw horizontally, and the two knobs should be turned simultaneously to draw a diagonal line. The task for the parent and child was to work together to draw a pine tree or a house by one of them turning one knob and the other turning the other. The researchers then analyzed videos of the interactions looking for indicators of the quality of the parent-child relationship. They found five aspects by which the interactions could be generally characterized: interactivity (e.g., child initiates interaction to which parent responds), parental control (parent physically or verbally controls child), attention towards partner (e.g., they look at each other), collaboration (they work on task together), and shared fun (e.g., parent and child laugh together).
"We found that the interactions of mobile-using children and their parents during joint play were of poorer quality than those of non-mobile-using children and their parents. There was less interactivity, less attention to each other and less parental control," summarizes Dr. Krisztina Liszkai-Peres.
However, the results of the questionnaire study show that joint, real-life (non-digital) activities help to prevent the child's mobile use to become problematic:
if the family spends more screen-free time together, it is less likely that the mobile-using child will become addicted
or that the child's mobile use will lead to regular family conflicts. However, shared digital activities have not been shown to be this effective, probably because they do not provide the high-quality social situations that are essential for the development of secure attachment and the various skills (e.g. self-regulation) that a child needs.
"There could be several factors behind the association. On the one hand, a child's use of digital devices takes time away from social activities, resulting in slower development of social skills, which may also manifest itself in parent-child interaction. In addition, we found that
children who use mobile devices tend to have parents who also engage in higher levels of digital media use,
leading to an overall decline in the family’s joint real-life activities, and thus a decline in the quality of interactions. However, there can also be an inverse causation: poorer parent-child relationships can lead to both parties paying more attention to digital devices," says Dr. Veronika Konok.
"It is important to note, however, that mobile phone use is not an evil thing itself. It is more important that even if children do use such a device, they have enough time for other non-digital activities such as exercise, sleep and, as the research shows, screen-free family time together. The latter can be seen as a protective factor against the development of problematic digital device use," said Dr. Krisztina Liszkai-Peres.
The researchers therefore recommend parents to engage with their children in as many screen-free activities as possible.
This will not only help their children develop personal relationships and social skills, but also prevent problematic device use. Parents have an exemplary role to play in media literacy. By following the right strategies, they can ensure a healthy and supportive environment for their children.
Association between the use of mobile touchscreen devices and the quality of parent-child interaction in preschoolers
Quantum crystal of frozen electrons—the Wigner crystal—is visualized for the first time
Princeton University researchers detect a strange form of matter that has eluded direct detection for some 90 years
PRINCETON UNIVERSITY
VIDEO:
THE VIDEO DESCRIBES MELTING PROCESSES OF AN ELECTRON WIGNER CRYSTAL INTO ELECTRON LIQUID PHASES. AS THE ELECTRON DENSITY (\NU, A MEASURE OF NUMBER OF ELECTRONS IN A MAGNETIC FIELD, IS CONTROLLED BY APPLYING ELECTRIC VOLTAGES) IS INCREASED, MORE ELECTRONS (DARK BLUE SITES) ENTER THE FIELD OF VIEW, AND A PERIODIC STRUCTURE OF A TRIANGULAR LATTICE EMERGES. THE PERIODIC STRUCTURE IS FIRST MELTED (NEAR \NU = 0.334) WHERE THE MAP SHOWS HOMOGENEOUS SIGNALS. AND THEN IT REAPPEARS AT HIGHER DENSITY \NU, AND EVENTUALLY MELTS AGAIN (\NU = 0.414).
Electrons—these infinitesimally small particles that are known to zip around atoms—continue to amaze scientists despite the more than a century that scientists have studied them. Now, physicists at Princeton University have pushed the boundaries of our understanding of these minute particles by visualizing, for the first time, direct evidence for what is known as the Wigner crystal—a strange kind of matter that is made entirely of electrons.
The finding, published in the April 11th issue of the journal Nature, confirms a 90-year-old theory that electrons can assemble into a crystal-like formation of their own, without the need to coalesce around atoms. The research could help lead to the discovery of new quantum phases of matter when electrons behave collectively.
“The Wigner crystal is one of the most fascinating quantum phases of matter that has been predicted and the subject of numerous studies claiming to have found at best indirect evidence for its formation,” said Al Yazdani, the James S. McDonnell Distinguished University Professor in Physics at Princeton University and the senior author of the study. “Visualizing this crystal allows us not only to watch its formation, confirming many of its properties, but we can also study it in ways you couldn’t in the past.”
In the 1930s, Eugene Wigner, a Princeton professor of physics and winner of the 1963 Nobel Prize for his work in quantum symmetry principles, wrote a paper in which he proposed the then-revolutionary idea that interaction among electrons could lead to their spontaneous arrangement into a crystal-like configuration, or lattice, of closely packed electrons. This could only occur, he theorized, because of their mutual repulsion and under conditions of low densities and extremely cold temperatures.
“When you think of a crystal, you typically think of an attraction between atoms as a stabilizing force, but this crystal forms purely because of the repulsion between electrons,” said Yazdani, who is the inaugural co-director of the Princeton Quantum Institute and director of the Princeton Center for Complex Materials.
For a long time, however, Wigner’s strange electron crystal remained in the realm of theory. It was not until a series of much later experiments that the concept of an electron crystal transformed from conjecture to reality. The first of these was conducted in the 1970s when scientists at Bell Laboratories in New Jersey created a “classical” electron crystal by spraying electrons on the surface of helium and found that they responded in a rigid manner like a crystal. However, the electrons in these experiments were very far apart and behaved more like individual particles than a cohesive structure. A true Wigner crystal, instead of following the familiar laws of physics in the everyday world, would follow the laws of quantum physics, in which the electrons would act not like individual particles but more like a single wave.
This led to a whole series of experiments over the next decades that proposed various ways to create quantum Wigner crystals. These experiments were greatly advanced in the 1980s and 1990s when physicists discovered how to confine electrons’ motion to atomically thin layers using semiconductors. The application of a magnetic field to such layered structures also makes electrons move in a circle, creating favorable conditions for crystallization. But these experiments were never able to directly observe the crystal. They were only able to suggest its existence or indirectly infer it from how electrons flow through the semiconductor.
“There are literally hundreds of scientific papers that study these effects and claim that the results must be due to the Wigner crystal,” Yazdani said, “but one can’t be sure, because none of these experiments actually see the crystal.”
An equally important consideration, Yazdani noted, is that what some researchers think is evidence of a Wigner crystal could be the result of imperfections or other periodic structures inherent to the materials used in the experiments. “If there are any imperfections, or some form of periodic substructure in the material, it is possible to trap electrons and find experimental signatures that are not due to the formation of a self-organized ordered Wigner crystal itself, but due to electrons ‘stuck’ near an imperfection or trapped because of the material’s structure,” he said.
With these considerations in mind, Yazdani and his research team set about to see whether they could directly image the Wigner crystal using a scanning tunneling microscope (STM), a device that relies on a technique called “quantum tunneling” rather than light to view the atomic and subatomic world. They also decided to use graphene, an amazing material that was discovered in the 21st century and has been used in many experiments involving novel quantum phenomena. To successfully conduct the experiment, however, the researchers had to make the graphene as pristine and as devoid of imperfections as possible. This was key to eliminating the possibility of any electron crystals forming because of material imperfections.
The results were impressive. “Our group has been able to make unprecedentedly clean samples that made this work possible,” Yazdani said. “With our microscope we can confirm that the samples are without any atomic imperfection in the graphene atomic lattice or foreign atoms on its surface over regions with hundreds of thousands of atoms.”
To make the pure graphene, the researchers exfoliated two carbon sheets of graphene in a configuration that is called Bernal-stacked bilayer graphene (BLG). They then cooled the sample down to extremely low temperatures—just a fraction of a degree above absolute zero—and applied a magnetic field perpendicular to the sample, which created a two-dimensional electron gas system within the thin layers of graphene. With this, they could tune the density of the electrons between the two layers.
“In our experiment, we can image the system as we tune the number of the electrons per unit area,” said Yen-Chen Tsui, a graduate student in physics and the first author of the paper. “Just by changing the density, you can initiate this phase transition and find electrons spontaneously form into an ordered crystal.”
This happens, Tsui explained, because at low densities, the electrons are far apart from each other—and they’re situated in a disordered, disorganized fashion. However, as you increase the density, which brings the electrons closer together, their natural repulsive tendencies kick in and they start to form an organized lattice. Then, as you increase the density further, the crystalline phase will melt into an electron liquid.
Minhao He, a postdoctoral researcher and co-first author of the paper, explained this process in greater detail. “There is an inherent repulsion between the electrons,” he said. “They want to push each other away, but in the meantime the electrons cannot be infinitely apart due to the finite density. The result is that they form a closely packed, regularized lattice structure, with each of the localized electron occupying a certain amount of space.”
When this transition formed, the researchers were able to visualize it using the STM. “Our work provides the first direct images of this crystal. We proved the crystal is really there and we can see it,” said Tsui.
However, just visualizing the crystal wasn’t the end of the experiment. A concrete image of the crystal allowed them to distinguish some of the crystal’s characteristics. They discovered that the crystal is triangular in configuration, and that it can be continuously tuned with the density of the particles. This led to the realization that the Wigner crystal is actually quite stable over a very long range, a conclusion that is contrary to what many scientists have surmised.
“By being able to continuously tune its lattice constant, the experiment proved that the crystal structure is the result of the pure repulsion between the electrons,” said Yazdani.
The researchers also discovered several other interesting phenomena that will no doubt warrant further investigation in the future. They found that the location to which each electron is localized in the lattice appears in the images with a certain amount of “blurring,” as if the location is not defined by a point but a range position in which the electrons are confined in the lattice. The paper described this as the “zero-point” motion of electrons, a phenomenon related to the Heisenberg uncertainty principle. The extent of this blurriness reflects the quantum nature of the Wigner crystal.
”Electrons, even when frozen into a Wigner crystal, should exhibit strong zero-point motion,” said Yazdani. “It turns out this quantum motion covers a third of the distance between them, making the Wigner crystal a novel quantum crystal.”
Yazdani and his team are also examining how the Wigner crystal melts and transitions into other exotic liquid phases of interacting electrons in a magnetic field. The researchers hope to image these phases just as they have imaged the Wigner crystal.
“Direct observation of a magnetic field-induced Wigner crystal,” by Yen-Chen Tsui, Minhao He, Yuwen Hu, Ethan Lake, Taige Wang, Kenji Watanabe, Takashi Taniguchi, Michael P. Zaletel, and Ali Yazdani was published April 11, 2024 in the journal Nature DOI to come.
Graduate student Yen-Chen Tsui, postdoctoral research associate Minhao He, and Yuwen Hu, who obtained her Ph.D. from the Princeton Department of Physics in 2023 and is now a postdoctoral fellow at Stanford, all contributed equal to this work. Other collaborators include, at the University of California-Berkeley, theoretical physicists Ethan Lake, Taige Wang, and Professor Michael Zaletel (also a member of the Material Science Division at Lawrence Berkeley National Laboratory), and Kenji Watanabe and Takashi Taniguchi from National Institute for Materials Science and International Center for Materials Nanoarchitectonics, respectively.
The work at Princeton was primarily supported by DOE-BES grant DE-FG02-07ER46419 and the Gordon and Betty Moore Foundation’s EPiQS initiative grants GBMF9469. Other support for the experimental infrastructure at Princeton was provided by NSF-MRSEC through the Princeton Center for Complex Materials NSF6 DMR- 2011750, ARO MURI (W911NF-21-2-0147), and ONR N00012-21-1-2592.
The team also acknowledges the hospitality of the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611, where part of this work was carried out. Work at UC Berkeley was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231, within the van der Waals Heterostructures Program (KCWF16).
An image of a triangular Wigner crystal taken by scanning tunneling microscope. Researchers have unveiled an elusive crystal that is formed purely from the repulsive nature of electrons. Each site (blue circular region) contains a single localized electron. Image by Yen-Chen Tsui and team, Princeton University
Direct observation of a magnetic-field-induced Wigner crystal
ARTICLE PUBLICATION DATE
10-Apr-2024
Physicists discover a novel quantum state in an elemental solid
Princeton University find that a crystal of arsenic hosts a new type of quantum behavior
PRINCETON UNIVERSITY
IMAGE:
A REPRESENTATION OF DATA VISUALIZATION OF QUANTUM STATES OF ELECTRONS ON THE SURFACE AND EDGE OF GREY ARSENIC CRYSTAL OBTAINED USING A SCANNING TUNNELING MICROSCOPE AT PRINCETON’S PHYSICS DEPARTMENT.
CREDIT: IMAGE BASED ON STM DATA SIMULATIONS PREPARED BY SHAFAYAT HOSSAIN AND THE ZAHID HASAN GROUP AT THE LABORATORY FOR TOPOLOGICAL QUANTUM MATTER AT PRINCETON UNIVERSITY.
Physicists have observed a novel quantum effect termed “hybrid topology” in a crystalline material. This finding opens up a new range of possibilities for the development of efficient materials and technologies for next-generation quantum science and engineering.
The finding, published in the April 10th issue of Nature, came when Princeton scientists discovered that an elemental solid crystal made of arsenic (As) atoms hosts a never-before-observed form of topological quantum behavior. They were able to explore and image this novel quantum state using a scanning tunneling microscope (STM) and photoemission spectroscopy, the latter a technique used to determine the relative energy of electrons in molecules and atoms.
This state combines, or “hybridizes,” two forms of topological quantum behavior—edge states and surface states, which are two types of quantum two-dimensional electron systems. These have been observed in previous experiments, but never simultaneously in the same material where they mix to form a new state of matter.
“This finding was completely unexpected,” said M. Zahid Hasan, the Eugene Higgins Professor of Physics at Princeton University, who led the research. “Nobody predicted it in theory before its observation.”
In recent years, the study of topological states of matter has attracted considerable attention among physicists and engineers and is presently the focus of much international interest and research. This area of study combines quantum physics with topology — a branch of theoretical mathematics that explores geometric properties that can be deformed but not intrinsically changed.
For more than a decade, scientists have used bismuth (Bi)-based topological insulators to demonstrate and explore exotic quantum effects in bulk solids mostly by manufacturing compound materials, like mixing Bi with selenium (Se), for example. However, this experiment is the first time topological effects have been discovered in crystals made of the element As.
“The search and discovery of novel topological properties of matter have emerged as one of the most sought-after treasures in modern physics, both from a fundamental physics point of view and for finding potential applications in next-generation quantum science and engineering,” said Hasan. “The discovery of this new topological state made in an elemental solid was enabled by multiple innovative experimental advances and instrumentations in our lab at Princeton.”
An elemental solid serves as an invaluable experimental platform for testing various concepts of topology. Up until now, bismuth has been the only element that hosts a rich tapestry of topology, leading to two decades of intensive research activities. This is partly attributed to the material's cleanliness and the ease of synthesis. However, the current discovery of even richer topological phenomena in arsenic will potentially pave the way for new and sustained research directions.
“For the first time, we demonstrate that, akin to different correlated phenomena, distinct topological orders can also interact and give rise to new and intriguing quantum phenomena,” Hasan said.
A topological material is the main component used to investigate the mysteries of quantum topology. This device acts as an insulator in its interior, which means that the electrons inside are not free to move around and therefore do not conduct electricity. However, the electrons on the device’s edges are free to move around, meaning they are conductive. Moreover, because of the special properties of topology, the electrons flowing along the edges are not hampered by any defects or deformations. This of type device has the potential not only of improving technology but also of generating a greater understanding of matter itself by probing quantum electronic properties.
Hasan noted that there is much interest in using topological materials for practical applications. But two important advances need to happen before this can be realized. First, quantum topological effects must be manifested at higher temperatures. Second, simple and elemental material systems (like silicon for conventional electronics) that can host the topological phenomena need to be found.
“In our labs we have efforts in both directions — we are searching for simpler materials systems with ease of fabrication where essential topological effects can be found,” said Hasan. “We are also searching for how these effects can be made to survive at room temperature.”
Background of the experiment
The discovery’s roots lie in the workings of the quantum Hall effect — a form of topological effect that was the subject of the Nobel Prize in Physics in 1985. Since that time, topological phases have been studied and many new classes of quantum materials with topological electronic structures have been found. Most notably, Daniel Tsui, the Arthur Legrand Doty Professor of Electrical Engineering, Emeritus, at Princeton, won the 1998 Nobel Prize in Physics for discovering the fractional quantum Hall effect. Similarly, F. Duncan Haldane, the Eugene Higgins Professor of Physics at Princeton, won the 2016 Nobel Prize in Physics for theoretical discoveries of topological phase transitions and a type of two-dimensional (2D) topological insulator. Subsequent theoretical developments showed that topological insulators can take the form of two copies of Haldane’s model based on electron’s spin-orbit interaction.
Hasan and his research team have been following in the footsteps of these researchers by investigating other aspects of topological insulators and searching for novel states of matter. This led them, in 2007, to the discovery of the first examples of three-dimensional (3D) topological insulators. Since then, Hasan and his team have been on a decade-long search for a new topological state in its simplest form that can also operate at room temperature.
“A suitable atomic chemistry and structure design coupled to first-principles theory is the crucial step to make topological insulator’s speculative prediction realistic in a high-temperature setting,” said Hasan. “There are hundreds of quantum materials, and we need both intuition, experience, materials-specific calculations and intense experimental efforts to eventually find the right material for in-depth exploration. And that took us on a decade-long journey of investigating many bismuth-based materials leading to many foundational discoveries.”
The experiment
Bismuth-based materials are capable, at least in principle, of hosting a topological state of matter at high temperatures. But these require complex materials preparation under ultra-high vacuum conditions, so the researchers decided to explore several other systems. Postdoctoral researcher Md. Shafayat Hossain suggested a crystal made of arsenic because it can be grown in a form that is cleaner than many bismuth compounds.
When Hossain and Yuxiao Jiang, a graduate student in the Hasan group, turned the STM on the aresenic sample, they were greeted with a dramatic observation — grey arsenic, a form of arsenic with a metallic appearance, harbors both topological surface states and edge states simultaneously.
“We were surprised. Grey arsenic was supposed to have only surface states. But when we examined the atomic step edges, we also found beautiful conducting edge modes,” said Hossain.
“An isolated monolayer step edge should not have a gapless edge mode,” added Jiang, a co-first author of the study.
This is what is seen in calculations by Frank Schindler, postdoctoral fellow and condensed matter theorist at the Imperial College London in the United Kingdom, and Rajibul Islam, a postdoctoral researcher at the University of Alabama in Birmingham, Alabama. Both are co-first authors on the paper.
“Once an edge is placed on top of the bulk sample, the surface states hybridize with the gapped states on the edge and form a gapless state,” Schindler said.
“This is the first time we have seen such a hybridization,” he added.
Physically, such a gapless state on the step edge is not expected for either strong or higher-order topological insulators separately, but only for hybrid materials where both kinds of quantum topology are present. This gapless state is also unlike surface or hinge states in strong and higher-order topological insulators, respectively. This meant that the experimental observation by the Princeton team immediately indicated a never-before-observed type of topological state.
David Hsieh, Chair of the Physics Division at Caltech and a researcher who was not involved in the study, pointed to the study’s innovative conclusions.
“Typically, we consider the bulk band structure of a material to fall into one of several distinct topological classes, each tied to a specific type of boundary state,” Hsieh said. “This work shows that certain materials can simultaneously fall into two classes. Most interestingly, the boundary states emerging from these two topologies can interact and reconstruct into a new quantum state that is more than just a superposition of its parts.”
The researchers further substantiated the scanning tunneling microscopy measurements with systematic high-resolution angle-resolved photoemission spectroscopy.
“The grey As sample is very clean and we found clear signatures of a topological surface state,” said Zi-Jia Cheng, a graduate student in the Hasan group and a co-first author of the paper who performed some of the photoemission measurements.
The combination of multiple experimental techniques enabled the researchers to probe the unique bulk-surface-edge correspondence associated with the hybrid topological state — and corroborate the experimental findings.
Implications of the findings
The impact of this discovery is two-fold. The observation of the combined topological edge mode and the surface state paves the way to engineer new topological electron transport channels. This may enable the designing of new quantum information science or quantum computing devices. The Princeton researchers demonstrated that the topological edge modes are only present along specific geometrical configurations that are compatible with the crystal’s symmetries, illuminating a pathway to design various forms of future nanodevices and spin-based electronics.
From a broader perspective, society benefits when new materials and properties are discovered, Hasan said. In quantum materials, the identification of elemental solids as material platforms, such as antimony hosting a strong topology or bismuth hosting a higher-order topology, has led to the development of novel materials that have immensely benefited the field of topological materials.
“We envision that arsenic, with its unique topology, can serve as a new platform at a similar level for developing novel topological materials and quantum devices that are not currently accessible through existing platforms," Hasan said.
The Princeton group has designed and built novel experiments for the exploration of topological insulators materials for over 15 years. Between 2005 and 2007, for example, the team led by Hasan discovered topological order in a three-dimensional bismuth-antimony bulk solid, a semiconducting alloy and related topological Dirac materials using novel experimental methods. This led to the discovery of topological magnetic materials. Between 2014 and 2015, they discovered and developed a new class of topological materials called magnetic Weyl semimetals.
The researchers believe this finding will open the door to a whole host of future research possibilities and applications in quantum technologies, especially in so-called “green” technologies.
“Our research is a step forward in demonstrating the potential of topological materials for quantum electronics with energy-saving applications,” Hasan said.
The team included numerous researchers from Princeton’s Department of Physics, including present and past graduate students Yu-Xiao Jiang, Maksim Litskevich, Xian P. Yang, Zi-Jia Cheng, Tyler Cochran, Nana Shumiya, and Daniel Multer, and present and past postdoctoral research associates Shafayat Hossain, Jia-Xin Yin, Guoqing Chang and Qi Zhang. The paper, “A hybrid topological quantum state in an elemental solid,” by Md Shafayat Hossain, Frank Schindler, Rajibul Islam, Zahir Muhammad, Yu-Xiao Jiang, Zi-Jia Cheng, Qi Zhang, Tao Hou, Hongyu Chen, Maksim Litskevich, Brian Casas, Jia-Xin Yin, Tyler A. Cochran, Mohammad Yahyavi, Xian P. Yang, Luis Balicas, Guoqing Chang, Weisheng Zhao, Titus Neupert and M. Zahid Hasan was published online in the April 10 issue of Nature (DOI: 10.1038/s41563-022-01304-3).
Primary support for the work at Princeton is from the U.S. Department of Energy (DOE) Office of Science, the National Quantum Information (NQI) Science Research Centers, the Quantum Science Center (QSC at ORNL) and Princeton University. Support from the U.S. DOE under the Basic Energy Sciences program (grant number DOE/BES DE-FG-02-05ER46200) was provided for the theory and advanced ARPES experiments. Support for advanced STM Instrumentation and theory work comes from the Gordon and Betty Moore Foundation (GBMF9461). Additional support is reported in the paper.
CREDIT: KNUT AND ALICE WALLENBERGS FOUNDATION/MAGNUS BERGSTRÖM
The potential of quantum technology is huge but is today largely limited to the extremely cold environments of laboratories. Now, researchers at Stockholm University, at the Nordic Institute for Theoretical Physics and at the Ca’ Foscari University of Venice have succeeded in demonstrating for the very first time how laser light can induce quantum behavior at room temperature –and make non-magnetic materials magnetic. The breakthrough is expected to pave the way for faster and more energy-efficient computers, information transfer and data storage.
Within a few decades, the advancement of quantum technology is expected to revolutionize several of society’s most important areas and pave the way for completely new technological possibilities in communication and energy. Of particular interest for researchers in the field are the peculiar and bizarre properties of quantum particles – which deviate completely from the laws of classical physics and can make materials magnetic or superconducting. By increasing the understanding of exactly how and why this type of quantum states arise, the goal is to be able to control and manipulate materials to obtain quantum mechanical properties.
So far, researchers have only been able to induce quantum behaviors, such as magnetism and superconductivity, at extremely cold temperatures. Therefore, the potential of quantum research is still limited to laboratory environments.
Now, a research team from Stockholm University and the Nordic Institute of Theoretical Physics (NORDITA)* in Sweden, the University of Connecticut and the SLAC National Accelerator Laboratory in USA, the National Institute for Materials Science in Tsukuba, Japan, the Elettra-Sincrotrone Trieste, the ‘Sapienza’ University of Rome and the Ca’ Foscari University of Venice in Italy, is the first in the world to demonstrate in an experiment how laser light can induce magnetism in a non-magnetic material at room temperature. In the study, published in Nature, the researchers subjected the quantum material strontium titanate to short but intense laser beams of a peculiar wavelength and polarization, to induced magnetism.
“The innovation in this method lies in the concept of letting light move atoms and electrons in this material in circular motion, so to generate currents that make it as magnetic as a refrigerator magnet. We have been able to do so by developing a new light source in the far-infrared with a polarization which has a “corkscrew” shape. This is the first time we have been able to induce and clearly see how the material becomes magnetic at room temperature in an experiment. Furthermore, our approach allows to make magnetic materials out of many insulators, when magnets are typically made of metals. In the long run, this opens for completely new applications in society,” says the research leader Stefano Bonetti at Stockholm University and at the Ca’ Foscari University of Venice
The method is based on the theory of “dynamic multiferroicity,” which predicts that when titanium atoms are “stirred up” with circularly polarized light in an oxide based on titanium and strontium, a magnetic field will be formed. But it is only now that the theory can be confirmed in practice. The breakthrough is expected to have broad applications in several information technologies.
“This opens up for ultra-fast magnetic switches that can be used for faster information transfer and considerably better data storage, and for computers that are significantly faster and more energy-efficient,” says Alexander Balatsky, professor of physics at NORDITA.
In fact, the results of the team have already been reproduced in several other labs, and a publication in the same issue of Nature demonstrates that this approach can be used to write, and hence store, magnetic information. A new chapter in designing new materials using light has been opened.
Contact: Stefano Bonetti, researcher at the Department of Physics, Stockholm University and professor of condensed matter physics at Ca’ Foscari University of Venice. E-mail: stefano.bonetti@fysik.su.se Phone: +46-8-553 786 55
Alexander Balatsky, professor of physics at the Nordic Institute for Theoretical Physics, NORDITA and at University of Connecticut, USA. E-mail: avb@nordita.org Phone: +46-701-917 870
The research project has been funded by the Knut and Alice Wallenberg Foundation and an ERC Synergy Grant.
* The Nordic Institute for Theoretical Physics (NORDITA) is a collaboration between the five Nordic countries. Since 2007, Nordita has been located at the Albanova university campus in Stockholm, with Stockholm University and KTH Royal Institute of Technology as the host universities.
