Correlated Electrons “Tango” in a Perovskite Oxide at the Extreme Quantum Limit
Originally published by Oak Ridge National Laboratory.
A team led by the Department of Energy’s Oak Ridge National Laboratory has found a rare quantum material in which electrons move in coordinated ways, essentially “dancing.” Straining the material creates an electronic band structure that sets the stage for exotic, more tightly correlated behavior — akin to tangoing — among Dirac electrons, which are especially mobile electric charge carriers that may someday enable faster transistors. The results are published in the journal Science Advances.
“We combined correlation and topology in one system,” said co-principal investigator Jong Mok Ok, who conceived the study with principal investigator Ho Nyung Lee of ORNL. Topology probes properties that are preserved even when a geometric object undergoes deformation, such as when it is stretched or squeezed. “The research could prove indispensable for future information and computing technologies,” added Ok, a former ORNL postdoctoral fellow.
In conventional materials, electrons move predictably (for example, lethargically in insulators or energetically in metals). In quantum materials in which electrons strongly interact with each other, physical forces cause the electrons to behave in unexpected but correlated ways; one electron’s movement forces nearby electrons to respond.
To study this tight tango in topological quantum materials, Ok led the synthesis of an extremely stable crystalline thin film of a transition metal oxide. He and colleagues made the film using pulsed-laser epitaxy and strained it to compress the layers and stabilize a phase that does not exist in the bulk crystal. The scientists were the first to stabilize this phase.
Using theory-based simulations, co-principal investigator Narayan Mohanta, a former ORNL postdoctoral fellow, predicted the band structure of the strained material. “In the strained environment, the compound that we investigated, strontium niobate, a perovskite oxide, changes its structure, creating a special symmetry with a new electron band structure,” Mohanta said.
Different states of a quantum mechanical system are called “degenerate” if they have the same energy value upon measurement. Electrons are equally likely to fill each degenerate state. In this case, the special symmetry results in four states occurring in a single energy level.
“Because of the special symmetry, the degeneracy is protected,” Mohanta said. “The Dirac electron dispersion that we found here is new in a material.” He performed calculations with Satoshi Okamoto, who developed a model for discovering how crystal symmetry influences band structure.
“Think of a quantum material under a magnetic field as a 10-story building with residents on each floor,” Ok posited. “Each floor is a defined, quantized energy level. Increasing the field strength is akin to pulling a fire alarm that drives all the residents down to the ground floor to meet at a safe place. In reality, it drives all the Dirac electrons to a ground energy level called the extreme quantum limit.”
Lee added, “Confined here, the electrons crowd together. Their interactions increase dramatically, and their behavior becomes interconnected and complicated.” This correlated electron behavior, a departure from a single-particle picture, sets the stage for unexpected behavior, such as electron entanglement. In entanglement, a state Einstein called “spooky action at a distance,” multiple objects behave as one. It is key to realizing quantum computing.
“Our goal is to understand what will happen when electrons enter the extreme quantum limit, where we find phenomena we still don’t understand,” Lee said. “This is a mysterious area.”
Speedy Dirac electrons hold promise in materials including graphene, topological insulators and certain unconventional superconductors. ORNL’s unique material is a Dirac semimetal, in which electron valence and conduction bands cross and this topology yields surprising behavior. Ok led measurements of the Dirac semimetal’s strong electron correlations.
“We found the highest electron mobility in oxide-based systems,” Ok said. “This is the first oxide-based Dirac material reaching the extreme quantum limit.”
That bodes well for advanced electronics. Theory predicts that it should take about 100,000 tesla (a unit of magnetic measurement) for electrons in conventional semiconductors to reach the extreme quantum limit. The researchers took their strain-engineered topological quantum material to Eun Sang Choi of the National High Magnetic Field Laboratory at the University of Florida to see what it would take to drive electrons to the extreme quantum limit. There, he measured quantum oscillations showing the material would require only 3 tesla to achieve that.
Other specialized facilities allowed the scientists to experimentally confirm the behavior Mohanta predicted. The experiments occurred at low temperatures so that electrons could move around without getting bumped by atomic-lattice vibrations. Jeremy Levy’s group at the University of Pittsburgh and the Pittsburgh Quantum Institute confirmed quantum transport properties. With synchrotron x-ray diffraction, Hua Zhou at the Advanced Photon Source, a DOE Office of Science user facility at Argonne National Laboratory, confirmed that the material’s crystallographic structure stabilized in the thin film phase yielded the unique Dirac band structure. Sangmoon Yoon and Andrew Lupini, both of ORNL, conducted scanning transmission electron microscopy experiments at ORNL that showed that the epitaxially grown thin films had sharp interfaces between layers and that the transport behaviors were intrinsic to strained strontium niobate.
“Until now, we could not fully explore the physics of the extreme quantum limit due to the difficulties in pushing all electrons to one energy level to see what would happen,” Lee said. “Now, we can push all the electrons to this extreme quantum limit by applying only a few tesla of magnetic field in a lab, accelerating our understanding of quantum entanglement.”
The title of the Science Advances paper is “Correlated Oxide Dirac Semimetal in the Extreme Quantum Limit.”
The DOE Office of Science supported the research. High magnetic field measurements were performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation and the state of Florida. The research used resources of the Advanced Photon Source, a DOE Office of Science user facility at Argonne National Laboratory; its extraordinary facility operations to provide beam time during the pandemic were supported in part by the DOE Office of Science through the National Virtual Biotechnology Laboratory, a consortium of DOE national laboratories focused on the response to COVID-19, with funding provided by the Coronavirus CARES Act.
UT-Battelle manages ORNL for the Department of Energy’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.
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Hyundai Motors is recalling 145,235 EVs and other “electrified” vehicles in the US, citing concerns about a loss of driving power, the National Highway Traffic Safety Administration (NHTSA) said on Friday.
The NHTSA announced this morning that the recall affects selected IONIQ 5 and IONIQ 6 EVs, as well as certain luxury Genesis models, including the GV60, GV70, and G80 electrified variants, from the 2022-2025 model years, Reuters reported.
It looks like the issue stems from “the integrated charging control units in these vehicles, which may become damaged and fail to charge the 12-volt battery. This malfunction could lead to a complete loss of drive power, posing safety risks for drivers,” the NHTSA stated.
If you’re an owner of one of these Hyundai models dating 2022-2025, stay tuned. Hyundai has not yet provided a timeline as to when affected vehicles will be repaired.
To make that happen, the company’s dealers will inspect and replace the charging unit and its fuse if necessary, NHTSA said. Free of charge, of course.
Importantly, no crashes, injuries, fatalities, or fires due to this issue have been reported in the US, Hyundai reported.
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Tesla announced that ‘Actually Smart Summon,’ its autonomous driving feature that enables moving its vehicles without anyone inside over short distances, is now being launched in Europe and the Middle East.
The automaker’s Full Self-Driving suite of features has been limited in those markets due to regulations and Tesla’s focus on making them work in North America first.
Actually Smart Summon is the vision-only version of Tesla’s “smart summon” feature, which was released years ago on Tesla vehicles with ultrasonic sensors.
When Tesla transitioned away from ultrasonic sensors, Smart Summon was one of the missing features that Tesla had yet to adapt to the vision-only (cameras and neural nets) system.
CEO Elon Musk said that it would be coming in 2022, but it finally came only a few months ago, in 2024.
However, that’s only in North America where Tesla focuses its Full Self-Driving (FSD) development, the feature package that includes Actually Smart Summon, also referred to as ‘ASS’.
Most of Tesla’s other markets, including Europe, don’t have the same capabilities under the Full Self-Driving package. That’s partly due to regulations, but Tesla also focuses on making the features work on North American roads first.
Now, Tesla has announced that its Actually Smart Summon feature is launching in Europe and the Middle East:
The feature can only be used on private roads, like parking lots and driveways. Most people have used it to bring their vehicles parked in a large parking lot to them as they exit a store or restaurant. However, the vehicle moves quite slowly under the feature and the owner needs to keep an eye on it at all time and be ready to cancel the summon as Tesla doesn’t take any responsibility for accidents caused by using Actually Smart Summon., like all other FSD features.
Therefore, most people I know who have the feature, myself included, tried once or try to see or impress some friends who have never seen a car move without anyone inside and then stopped using it.
The feature’s main useful use-case is for people with extremely tight parking spots. It enables them to exit the vehicle before it is in its final parking spot and then move the car in and out remotely.
However, that has been the case for years with the regular Smart Summon, as you generally don’t need the vehicle to handle complex parking lots. You mostly need it to move a few feet forward or backward.
But a recent update has broken this feature for some people. We recently reported on a very unfortunate situation that resulted in a Tesla owner having to get out of his car through his trunk.
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US Automakers are planning to ask Mr. Trump to retain President Biden’s EPA exhaust rules, in the face of signs that Mr. Trump might try to reverse them. If the rules are reversed, it would cost Americans hundreds of billions of dollars and thousands of deaths per year.
Interestingly, this is the opposite of what big auto did the last time a reality TV show came to the White House – signaling that they have perhaps learned their lesson this time ’round.
First, some history.
In the middle of the 20th century, the effects of human activity on the atmosphere became readily apparent. Certain cities – with Los Angeles among the forefront – were choked by smog, and it was soon found out that vehicle pollution was the primary reason for this smog.
Since Los Angeles was one of the most smog-choked cities, California led the way on clean air regulation, creating the California Air Resources Board in 1967 (under then-Governor Ronald Reagan).
The federal government gave California special dispensation to set stricter regulations than the rest of the country, in recognition that it had a unique smog problem in its primary metropolis. California has retained this dispensation, in the form of a “waiver,” since then. And other states can follow California’s rules, but only if they copy all of the rules exactly.
Thus, there have been two separate sets of clean air regulation in this country since then – the federal rules, and then the “CARB states” which follow California’s rules.
In 2012 that finally changed, when President Obama’s EPA negotiated with California to finally harmonize these standards and also implement higher fuel efficiency nationwide. This would have been a huge boon for both industry and consumers, saving money and giving regulatory certainty to the auto industry.
But then, in 2016, the candidate who got the 2nd most votes in the presidential election was headed for the White House. And automakers responded by immediately lobbying to torpedo these standards, even before inauguration.
Now, you might think that asking a profoundly ignorant individual, who ended up staffing the EPA with bought-and-sold science deniers (huh, that would never happen again would it?), to change rules which had already been set through years of negotiation and lobbying was not a great idea. And you’d be right.
Not long after automakers had the dumb idea to ask an idiot to fix something that wasn’t broken, that idiot went and broke things further, fracturing the agreement between California and the federal government and ensuring less regulatory certainty for automakers.
After realizing their blunder (which they could have avoided by, y’know, thinking at all about it beforehand), big auto relented and asked the government to please not implement the rollbacks automakers had asked for. Some companies even forged their own agreement with California.
But it was too late, and we are now back in the era of disparate regulatory regimes – something which John Bozzella, head of the Alliance for Automotive Innovation (formerly called Global Automakers), keeps complaining about these days, despite having lobbied for exactly this in the first place.
The US EPA and California are still not fully harmonized, but both released recent new standards which do have somewhat similar targets. If a manufacturer builds towards one set of rules, they’ll probably not be too far off from meeting the other.
So in the end, we did get better emissions regulations and California has continued to push forward with clean air regulations, thus signaling a failure on the part of Mr. Trump to cause the long term harm to Americans that he and his oil industry solicitors so desperately seem to desire.
The most recent EPA standards, finalized in March (after being softened at the auto industry’s request), do not mandate any particular powertrain, but rather require steep emissions cuts – and EVs are the easiest way to achieve lower emissions.
Notably, Tesla lobbied in favor of making this last set of standards stronger, and they also lobbied against ruining the Obama/CA standards in 2016 – being one of very few automakers who were on the correct side of that discussion.
Despite that the President Biden EPA’s rules do not mandate any particular powertrain, Mr. Trump, in his usual ignorance, has said that he will end the nonexistent EV mandate. And now that he has received more votes than his opponent for the first time (after three tries, and despite committing treason in 2021 for which there is a clear legal remedy), it looks like the upcoming EPA might be directed to end these emissions cuts and fuel/health cost savings for Americans.
But in this instance, it sounds like the automakers might actually do the right thing for once, and ask the government not to do any rollbacks, and instead let them continue on with the plans without disruption from a convicted felon who seems determined to cede a US EV manufacturing boom back to China.
Detroit’s Big Three automakers – GM, Ford and Stellantis – are all reportedly trying to figure out how to ensure that these rules stay in place. The mentality is that constantly changing regulations are not beneficial for companies – particularly in the auto realm, where models take on the order of 7 years to plan and execute. Long-term planning is important for the hundreds of billions in manufacturing investment that EVs have attracted in the US during Biden’s EV push.
These attitudes are notable, given that this is not what automakers did in 2016/2017. That time, they compulsively pushed for fewer regulations, and now they are asking for regulations to remain in place.
It’s further notable that Tesla CEO Elon Musk, whose company lobbied strongly in favor of emissions cuts and makes more use of the federal EV tax credit than any other company, is now allied with the very entity that’s looking to harm EVs. It seems that we have entered opposite world.
So it remains to be seen where we will go from here – on the one hand, doctors, nurses, scientists, environmental groups, many businesses, people who recognize that they have lungs which they would like to continue using, and so on, generally support the strongest regulation possible. Now, automakers have been added to the pile asking for strong regulations.
On the other hand, a former reality TV host – tagged along with by the CEO of the company that has sold more electric cars than any other – seem determined to kill electric cars, despite the harm that would cause to Americans’ pocketbooks and health insurance premiums. And that famously vindictive character may be even more spurred towards this harmful course of action after failing in his efforts the first time.
Who ya got?
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