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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Environment
Fintechs like Block and PayPal are battling like never before to be your all-in-one online bank
Jack Dorsey, co-founder of Twitter Inc., speaks during the Bitcoin 2021 conference in Miami, Florida, U.S., on Friday, June 4, 2021.
Eva Marie Uzcategui | Bloomberg | Getty Images
Jack Dorsey’s Block got started as Square, offering small businesses a simple way to accept payments via smartphone. Affirm began as an online lender, giving consumers more affordable credit options for retail purchases. PayPal upended finance more than 25 years ago by letting businesses accept online payments.
The three fintechs, which were each launched by tech luminaries in different eras of Silicon Valley history, are increasingly converging as they seek to become virtual all-in-one banks. In their latest earnings reports this month, their lofty ambitions became more clear than ever.
Block was the last of the three to report, and the high-level numbers were troubling. Earnings and revenue missed estimates, sending the stock down 18%, its steepest drop in five years. But to hear Dorsey discuss the results, Block is successfully implementing a strategy of offering consumers the ability to pay businesses by smartphone, send money to friends through Cash App, and access credit and debit services while also getting more ways to invest in bitcoin.
“In 2024, we expanded Square from a payments tool into a full commerce platform, enhanced Cash App’s financial services offerings, and restructured our organization,” Dorsey said on Block’s earnings call on Thursday after the bell.
Block and an expanding roster of fintech rivals have all come to see that their moats aren’t strong enough in their core markets to keep the competition away, and that the path to growth is through a diverse set of financial services traditionally offered by banks. They’re playing to an audience of digital-first consumers who either didn’t grow up using a brick-and-mortar bank or realized at an early age that they had no need to ever set foot in a physical branch, or to meet with a loan officer or customer service rep.
“Longer term, we see a significant opportunity to grow actives, particularly among that digital-native audience like Millennial and Gen Z,” Block CFO Amrita Ahuja said on the earnings call.
As part of its expansion, Block has encroached on Affirm’s turf, with an increasing focus on buy now, pay later (BNPL) offerings that it picked up in its $29 billion purchase of Afterpay, which closed in early 2022. Block’s market share in BNPL increased by one point to 19%, while Affirm held its position at 17%, according to a recent report from Mizuho. Both companies are outperforming Klarna in BNPL, the report said.
Block’s BNPL play is now tied into Cash App, with an integration activated this week that gives users another way to make purchases through a single app. With Cash App monthly active users stagnating at 57 million for the last few quarters, the company is focused on engagement rather than rapid user acquisition.
“We think that there is significant opportunity for growth longer term, but there are some deliberate decisions we’ve made as part of our banker-based strategy in the near term” that have kept user numbers from increasing, Ahuja said. “This is a part of our continuous enhancements to drive healthy customer engagement as we bank our base.”
Compared to Block, Wall Street had a very different reaction to Affirm’s earnings earlier this month, pushing the stock up 22% after the company’s results sailed past estimates.
Affirm founder and CEO Max Levchin, who was previously a co-founder of PayPal, built his company with the promise of giving consumers lower-cost and easy-to-tap intstallment loans for purchases like electronics, jewelry and travel.
The BNPL battlefront
In its latest earnings report, Affirm posted a 35% increase in gross merchandise volume to $10.1 billion. Revenue surged 47% to $770 million, while its active consumer base grew 23% to 21 million.
Beyond BNPL, Levchin has pushed Affirm into debit with the Affirm Card, which now has 1.7 million active users, up 136% year-over-year.
“Anything we can do to personalize the experience, to give people a chance to feel like this is the best alternative they have to their debit or their credit card is what we’re busy with,” Levchin said on the earnings call. He said the goal is to get the card to 20 million users, spending on average $7,500 per year.
Affirm is also partnering with FIS to bring its debit card functionality to traditional banks.
Levchin left PayPal in 2002, after the company was acquired by eBay. It was a decade before he’d start working to help popularize the modern day BNPL market.
Now his former employer, which spun back out from eBay in 2015, is in on the BNPL game.
Under the leadership of CEO Alex Chriss, who took over the company in September 2023, PayPal is in the midst of a turnaround that involves working to better monetize products like Braintree and Venmo and joining the world of physical commerce with a debit card inside its mobile app.
Investors responded positively in 2024, pushing the stock up almost 40% after a brutal few years. But the stock dropped 13% after its earnings report, even as profit and revenue were better than expected. PayPal’s total payment volume for the quarter hit $437.8 billion, slightly below projections, while transaction margins rose to 47% from 45.8% — a sign of improving profitability.
One of Chriss’ big pushes is to get more out of Venmo, which has long been a popular way for friends to pay each other but hasn’t been a big hit with businesses. Venmo’s total payment volume in the quarter rose 10% year-over-year, with increased adoption at DoorDash, Starbucks, and Ticketmaster.
PayPal is also promoting Venmo’s debit card and “Pay With Venmo,” which saw 30% and 20% monthly active growth in 2024, respectively. The company is introducing new services to improve merchant retention, including its Fastlane one-click checkout feature, designed to compete with Apple Pay and Shopify’s Shop Pay.
Last year, the company launched PayPal Everywhere, a cashback-driven initiative designed to boost engagement within its mobile app. Chriss said on the earnings call that it’s “driving significant increases in debit card adoption and opening new categories of spend.”
As with virtually all financial services products, the new offerings from Block, Affirm and PayPal are designed to produce growth but not at the expense of profit. Banks operate at low margins, in large part because there’s so much competition for lower-priced loans and better cash-back options. There’s also all the costs associated with underwriting and compliance.
That’s the environment in which fintechs have to operate, though without the costs of running a network of physical branches.
Levchin talks about helping customers spend less, not more. And Block acknowledges the need for hefty investments to reach the company’s desired outcome.
“This is a part of our continuous enhancements to drive healthy customer engagement as we bank our base,” Ahuja said. “We’ve made investments in critical areas like compliance, support and risk. And as we’ve done that, we’ve progressed more of our actives through our identity verification process, which in turn, unlocks greater access to those actives to our full suite of financial tools.”
The Trump administration is shutting down EV chargers at all federal government buildings and is also expected to sell off the General Services Administration‘s (GSA) newly bought EVs.
GSA, which manages all federal government-owned buildings, also operates the federal buildings’ EV chargers. Federally owned EVs and federal employee-owned personal EVs are charged on those 8,000 charging ports.
The Verge reports it’s been told by a source that plans will be officially announced internally next week, and it’s seen an email that GSA has already sent to regional offices about the plans:
“As GSA has worked to align with the current administration, we have received direction that all GSA-owned charging stations are not mission-critical.”
The GSA is working on the timing of canceling current network contracts that keep the EV chargers operational. Once those contracts are canceled, the stations will be taken out of service and “turned off at the breaker,” the email reads. Other chargers will be turned off starting next week.
“Neither Government Owned Vehicles nor Privately Owned Vehicles will be able to charge at these charging stations once they’re out of service.”
Colorado Public Radio first reported yesterday that it had seen the email that was sent to the Denver Federal Center, which has 22 EV charging stations at 11 locations.
The Trump/Elon Musk administration has taken the GSA’s fleet electrification webpage offline entirely. (An archived version is available here.)
The Verge‘s source also said that the GSA will offload the EVs it bought during the Biden administration, although it’s unknown whether they’ll be sold or stored.
Read more: Trump just canceled the federal NEVI EV charger program
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Ben Zhou, chief executive officer of ByBit, during the Token2049 conference in Singapore, on Thursday, Sept. 14, 2023.
Joseph Nair | Bloomberg | Getty Images
Bybit, a major cryptocurrency exchange, has been hacked to the tune of $1.5 billion in digital assets, in what’s estimated to be the largest crypto heist in history.
The attack compromised Bybit’s cold wallet, an offline storage system designed for security. The stolen funds, primarily in ether, were quickly transferred across multiple wallets and liquidated through various platforms.
“Please rest assured that all other cold wallets are secure,” Ben Zhou, CEO of Bybit, posted on X. “All withdrawals are NORMAL.”
Blockchain analysis firms, including Elliptic and Arkham Intelligence, traced the stolen crypto as it was moved to various accounts and swiftly offloaded. The hack far surpasses previous thefts in the sector, according to Elliptic. That includes the $611 million stolen from Poly Network in 2021 and the $570 million drained from Binance in 2022.
Analysts at Elliptic later linked the attack to North Korea’s Lazarus Group, a state-sponsored hacking collective notorious for siphoning billions of dollars from the cryptocurrency industry. The group is known for exploiting security vulnerabilities to finance North Korea’s regime, often using sophisticated laundering methods to obscure the flow of funds.
“We’ve labelled the thief’s addresses in our software, to help to prevent these funds from being cashed-out through any other exchanges,” said Tom Robinson, chief scientist at Elliptic, in an email.
The breach immediately triggered a rush of withdrawals from Bybit as users feared potential insolvency. Zhou said outflows had stabilized. To reassure customers, he announced that Bybit had secured a bridge loan from undisclosed partners to cover any unrecoverable losses and maintain operations.
The Lazarus Group’s history of targeting crypto platforms dates back to 2017, when the group infiltrated four South Korean exchanges and stole $200 million worth of bitcoin. As law enforcement agencies and crypto tracking firms work to trace the stolen assets, industry experts warn that large-scale thefts remain a fundamental risk.
“The more difficult we make it to benefit from crimes such as this, the less frequently they will take place,” Elliptic’s Robinson wrote in a post.
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