Condensed matter

Tiancheng Song awarded Lee Osheroff Richardson Science Prize

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This post is slightly adapted from one originally published by Oxford Instruments

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Tiancheng Song

Oxford Instruments announced Feb 15 that Tiancheng Song, who will join the UW–Madison physics department as an assistant professor in May, has been awarded the 2024 Lee Osheroff Richardson Science Prize. He is currently an experimental physicist and Dicke Fellow at Princeton University.

Dr. Song is recognized for his efforts in developing and employing various measurement techniques at low temperatures and in magnetic fields to study 2D superconductivity and magnetism in van der Waals heterostructures. His works have uncovered a series of emergent quantum phenomena in 2D superconducting and magnetic systems.

The Lee Osheroff Richardson Science Prize promotes and recognises the novel work of young scientists working in the fields of low temperatures and/or high magnetic fields or surface science in North and South America.

“I am thrilled to be the recipient of the prestigious Lee Osheroff Richardson Science Prize this year! I feel this is a special honour because I am joining the ranks of remarkable scientists who have been awarded this prize for their famous experiments and achievements,” commented Dr. Song.

Tiancheng Song is currently a Dicke Fellow in the Department of Physics at Princeton University. Working with Prof. Sanfeng Wu, Dr. Song recently developed a new technique to investigate 2D superconductivity, strongly correlated phases and the associated unconventional quantum phase transition.

In his work at Princeton, Dr. Song successfully measured superconducting quantum fluctuations of monolayer WTe2 based on the vortex Nernst effect. The result led to the discovery of a new type of quantum critical point beyond the conventional Ginzburg-Landau theory and demonstrated a new sensitive probe to 2D superconductivity and superconducting phase transitions.

Dr. Song’s results have been well recognized by the community with his work being cited over 4,000 times. Dr. Song’s original contributions are demonstrated by the faculty offers he has subsequently received; he will join the University of Wisconsin–Madison as an assistant professor in May 2024.

As part of the prize, Dr. Song will receive $8000 as well as support to attend the APS March Meeting in Minneapolis where he will be presented his award.

The 2024 LOR Science Prize selection committee is chaired by Professor Laura Greene, NHMFL and FSU and includes: Professor Hae-Young Kee, Toronto University; Professor Collin Broholm, Johns Hopkins University; Professor Paula Giraldo-Gallo, University of the Andes; and Dr Xiaomeng Liu, Princeton (2023 winner).

About the LOR Science Prize

Oxford Instruments is aware that there is a critical and often difficult stage for many scientists between completing a PhD and gaining a permanent research position. The company is pleased to help individuals producing innovative work by offering financial assistance and suitably promoting their research work, through sponsoring the LOR Science Prize for North and South America for the past 19 years. The Prize is named in honour of Professors David M. Lee, Douglas D. Osheroff and Robert C. Richardson, joint recipients of The Nobel Prize in Physics 1996 for their discovery of ‘superfluidity in helium-3’.

The previous winners of the LOR Science Prize are Dr Xiaomeng Liu, Dr James Nakamura, Dr Matthew Yankowitz, Dr Sheng Ran, Dr Paula Giraldo-Gallo, Dr Kate Ross, Dr Brad Ramshaw, Dr Mohamad Hamidian, Dr Cory Dean, Dr Chiara Tarantini, Dr Lu Li, Dr Kenneth Burch, Dr Jing Xia, Dr Vivien Zapf, Dr Eunseong Kim, Dr Suchitra Sebastian, Dr Jason Petta, and Dr Christian Lupien.

A new spin on an old superconductor means that it can be an ideal spintronic material, too

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Back in the 1980s, researchers discovered that a bismuthate oxide material was a rare type of superconductor that could operate at higher temperatures. Now, a team of engineers and physicists at the University of Wisconsin-Madison has found the material, “Ba(Pb,Bi)O3,” is unique in another way: It exhibits extremely high spin orbit torque, a property useful in the emerging field of spintronics.

The combination makes this and similar materials potentially important in developing the next generation of fast, efficient memory and computing devices.

The finding was an encouraging surprise to Chang Beom-Eom, a professor of materials science and engineering, and Mark Rzchowski, a professor of physics, both at UW-Madison. “We’re looking to expand the range of materials that can be used in spintronic applications,” says Rzchowski. “We had known from previous work these oxides have a lot of interesting properties, and so were investigating the spintronic characteristics. We weren’t anticipating such a large effect. The origins of this are not theoretically understood, but we can speculate about some interesting physical mechanisms.”

The paper was published Dec. 5, 2023, in the journal Nature Electronics.

In conventional electronics, positive and negative electric charges are used to flip millions or billions of tiny transistors on semiconductor chips or in memory devices. But in spintronics, magnetic fields, and interactions with other electrons, manipulate a fundamental property of electrons called the spin state, which records information. This is much faster, more energy-efficient and more powerful than current semiconductors and will advance the development of quantum computing and low-power devices.

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Featured image caption: Chang Beom-Eom, a professor of materials science and engineering, and Mark Rzchowski, a professor of physics, in the lab. Photo: Joel Hallberg.

Ben Woods and team named finalists in 2023 WARF Innovation Awards

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Each fall the WARF Innovation Awards recognize some of the best inventions at UW–Madison. WARF receives hundreds of new invention disclosures each year. Of these disclosures, the WARF Innovation Award finalists are considered exceptional in the following criteria:

  • Has potential for high long-term impact
  • Presents an exciting solution to a known important problem
  • Could produce broad benefits for humankind

One of the six finalists comes from Physics. Research Associate Benjamin Woods and a team including Distinguished Scientist Mark Friesen, John Bardeen Prof. of Physics Mark Eriksson, Honorary Associate Robert Joynt, and Graduate Student Emily Joseph developed a quantum device that shows a significant increase in valley splitting, a key property needed for error-free quantum computing. The device features a novel structural composition that turns conventional wisdom on its head.

Two winners, selected from the six finalists, will be announced in WARF’s annual holiday greeting; sign up to receive the greeting here. Each of the two Innovation Award winners receive $10,000, split among UW inventors.

Victor Brar earns NSF CAREER award

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Congrats to associate professor Victor Brar on earning an NSF CAREER award! CAREER awards are NSF’s most prestigious awards in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization.

Victor Brar

For this award, Brar will study the flow of electrons in 2D materials, or materials that are only around one atom thick. His group has already shown that when they applied a relatively old technique — scanning tunneling potentiometry, or STP — to 2D materials such as graphene, they could create unexpectedly high-contrast images, where they could track the movement of individual electrons when an electric current was applied. They found that electrons flow like a viscous fluid, a property that had been predicted but not observed directly.

“So now instead of applying electrical bias, we’ll apply a thermal bias, because we know things move from hot to cold, and then image how [electrons] move in that way,” Brar says. “Part of what’s driving this idea is that Professor Levchenko has predicted that if you image the way heat flows through a material, it should also behave hydrodynamically, like a liquid, rather than diffusive, which is how you might imagine it.”

One motivation for this research is to better understand the general flow of fluids, a problem that is often too complex for supercomputers to solve correctly. Because STP visualizes the fluid-like flow of electrons directly, Brar envisions this work as potentially providing a way of solving  fluid mechanics problems by directly imaging flow, without the need of simulations, similar to what is done in wind tunnels.

“Also, there are these predicted phases of electrons that no one has observed before,” Brar says. “We want to be the first to observe them.”

In addition to an innovative research component, NSF proposals require that the research has broader societal impacts, such as working toward greater inclusion in STEM or increasing public understanding of science. Brar’s group is using haptic pens, devices that are commonly used in remote trainings for surgeons and in the gaming community because they give a gentle push back that mimics a realistic touch. By attaching the haptic pen to a scanning tunneling microscope (STM), people holding the pen can “feel” the individual atoms and surfaces that the STM is touching.

“We think materials science is one of those areas where feeling the forces that hold matter together may provide more intuitive than looking at equations,” Brar says. “We’re making virtual crystal lattices that you can touch with the haptic pen and feel how the atoms fix together, but we’re also making it so you can feel the different forces of the different atoms used.”

Brar plans to introduce the haptic pen and atom models into Physics 407 and develop a materials science module for the UW Alumni Association’s Grandparents University. And because the haptic pen relies almost entirely on touch, Brar plans to work with the Wisconsin Council of the Blind and Visually Impaired to improve access to materials science instruction for people with vision impairments.

 

 

Congrats to Prof. Joynt on his retirement!

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37 years after joining the faculty of the department of physics at the University of Wisconsin–Madison, Prof. Bob Joynt has announced his retirement at the end of July.

Joynt is a condensed matter theorist who began as an assistant professor in 1986. His early work focused largely on superconductivity, including high temperature superconductors. He also played an important role in better understanding the Quantum Hall effect, dating back to his graduate work and continuing here. After a decade and a half, his career took a fortuitous turn when he wrote a quantum computing grant proposal with physics professor Mark Eriksson and other researchers in engineering.

profile photo of Bob Joynt
Prof. Bob Joynt

“That was really a pivotal point in my career, and I’ve been doing quantum computing mostly ever since,” Joynt recalls. “Change is good, I found. I enjoyed that change and I’m glad I did it.”

His work for the past 20 years has mainly focused on understanding the origins of noise and decoherence in quantum systems and in the design of semiconductor structures for quantum computing. Joynt is a fellow of the American Physical Society and a UW–Madison Romnes Faculty Fellow. He has co-authored over 175 peer-reviewed publications and trained 26 doctoral students, in addition to numerous postdocs and MS Physics­–Quantum Computing students.

Joynt’s academic and research achievements alone comprise an illustrious career that any retiring professor would likely be happy with. Still, his contributions to the department span so much more.

Joynt served as department chair from 2011-2014, for which he focused his efforts on department fundraising. He was responsible for starting the Board of Visitors, a group of people, mostly in industry, with strong ties to the department. The BoV advises and assists on department priorities, plays a leading role in fundraising, and provides a professional network for current students and alumni. From 2017-2022, Joynt additionally served as the department’s Associate Chair for Alumni Relations and the Board of Visitors.

a man stands near a white board looking at an unpictured audience. He is holding a wood pointer in his right hand and gesturing with his left hand.
Prof. Joynt lectures in this undated photo from earlier in his career

Around 2016, Joynt noted that doctoral students with quantum computing research experience were in such high demand that employers were often entering bidding wars for them. Was there a way to meet the demands of the quantum computing workforce by training students in a year or two? And so, thanks to Joynt’s vision and persistence, the MS in Physics–Quantum Computing program — the first MS in quantum computing in the U.S. — enrolled its first cohort in Fall 2019.

“We take about 25-30 PhD students each year, and now we take about the same number of MSQPC students,” Joynt says. “It’s become a big part of the department’s educational program.”

Adds Mark Eriksson, Department Chair and John Bardeen Professor of Physics: “Our department’s MSPQC program was the first in the nation and remains a model for others, thanks to Professor Joynt’s vision and energy.”

The department boasts the oldest hands-on science museum in the country — a claim we now feel confident making thanks to Joynt’s extensive research on the history of the Ingersoll Physics Museum for its 100th anniversary in 2018. The museum and physics outreach in general have always been important to Joynt. He has served in an informal capacity as faculty lead for the museum for several years now, helping to raise funds and ensure the museum fulfills its mission of providing free, hands-on, inquiry-based exhibits.

When asked what he wanted to be remembered for in the department, Joynt reflected on lessons from his career and then looked forward: “My advice to the department is: do new things. Don’t be afraid of change. Science changes, education changes, all these things are changing, and you need to change with them.”

Joynt’s retirement is official as of July 31, but he emphasizes that he is only retiring from administrative and teaching duties. He plans to continue his research efforts, sometimes in Madison and often abroad.

Mark Friesen, a senior scientist and long-time collaborator of Joynt’s, says he looks forward to continuing to work with Joynt in this new stage of his career, adding:

“When I joined the department, I knew Bob through reputation as one of the bright condensed matter physicists of his generation. I feel very fortunate to have worked with him, first as a mentor, and later as a colleague. Bob has a tremendous intuition for condensed matter that spans far beyond his immediate research efforts. He also has an easy-going and gracious style that draws in collaborators, and he is just fun to interact with, both inside and outside the department.”

 

Keith Bechtol, Victor Brar promoted to Associate Professors

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Congratulations to Keith Bechtol and Victor Brar, who were both promoted to associate professors of physics with tenure!

profile photo of keith bechtol
Keith Bechtol

Bechtol is an observational cosmologist with research interests in dark matter and dark energy, using the whole Universe as a lab to understand the fundamental physics of nature. He is part of the Dark Energy Survey (DES) that has cataloged more 500 million galaxies and thousands of supernovae to understand the nature of dark energy. He and his group are also working on the construction and commissioning of the Vera C. Rubin Observatory in preparation for the Legacy Survey of Space and Time (LSST). LSST is expected to catalog more stars, more galaxies and more solar system objects during its first year of operations than all previous telescopes combined.

“Professor Bechtol plays a leading role in the Vera C. Rubin Observatory, which is now poised to enable a major leap in the data available for understanding the development of our universe,” says Mark Eriksson, Chair and John Bardeen Professor of Physics.

Bechtol was a co-convener of the DES’s Science Release Working Group for four years and a co-convener of the Milky Way Working Group for two years. He is now serving as Technical Coordinator for the LSST Dark Energy Science Collaboration. In 2022, he was selected to the Department of Energy’s Early Career Research Program. He also proposed and is the faculty lead for the physics department’s Thaxton Fellowship, whose goal is to provide more equitable access to physics research experiences for undergraduates.

Victor Brar

Brar, the Van Vleck professor of physics and a member of the Wisconsin Quantum Institute, is an experimental condensed matter physicist with a research focus on quantum materials and novel imaging techniques. His group works on developing metamaterials such as 2D materials for use in laser sailing or fabricating graphene structures for use in telecommunications. They also use scanning tunneling microscopy and scanning tunneling potentiometry to understand the physical and electrical properties of materials.

“The experiments performed by Professor Brar and his research team have enabled measurements of completely new regimes for electron transport in 2D materials,” Eriksson says.

Brar was awarded a Moore Inventor Fellowship in 2018, a Sloan Fellowship in 2021, and a National Science Foundation CAREER award in 2023. He has additionally received two UW–Madison Research Forward awards.

Alex Levchenko honored with H.I. Romnes Fellowship

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This post is modified from one originally published by the Office of the Vice Chancellor for Research and Graduate Education

 

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Alex Levchenko

Physics professor Alex Levchenko was one of thirty-five of the University of Wisconsin–Madison faculty to be awarded fellowships from the Office of the Vice Chancellor for Research and Graduate Education for 2023-24. The awardees span the four divisions on campus: arts and humanities, physical sciences, social sciences and biological sciences.

“These awards recognize our faculty research, academic and outreach successes and provide an opportunity for continued development of their outstanding research programs,” says Steve Ackerman, vice chancellor for research and graduate education. “I’m grateful that we are able to recognize invest in these faculty in this way, and I look forward to seeing the results of their imaginative use of these funds.”

The awards are possible due to the research efforts of UW–Madison faculty and staff. Technology that arises from these efforts is licensed by the Wisconsin Alumni Research Foundation and the income from successful licenses is returned to the OVCRGE, where it’s used to fund research activities and awards throughout the divisions on campus.

Eighteen faculty, including Levchenko, have been honored with the H.I. Romnes Fellowships to recognize faculty with exceptional research contributions within their first six years from promotion to a tenured position. The award is named in recognition of the late WARF trustees president H.I. Romnes and comes with $60,000 that may be spent over five years.

Levchenko studies fundamental aspects of condensed matter physics with a focus on electronic phases of matter and quantum transport. Specific areas of expertise include superconductivity, topological order, and nanoscale systems such as graphene and other van der Waals materials. He is a Fellow of the American Physical Society and of the Alexander von Humboldt Foundation, and recipient of an early career grants from the National Science Foundation and the Binational Science Foundation. His teaching covers all levels of undergraduate and graduate education, and he serves on multiple professional review panels internationally.

Victor Brar, Wisconsin Center for Semiconductor Thermal Photonics earn UW Research Forward funding

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Sixteen projects were chosen in the third round of UW–Madison’s Research Forward competition, including one from Physics.

The Wisconsin Center for Semiconductor Thermal Photonics will explore fundamental science at the intersection of semiconductor technology and radiative heat transfer. This cross-disciplinary center will explore thermal radiation in unconventional semiconductor materials, in nanostructures, and in extreme conditions, and achieve control of the directionality and timing of radiative heat transfer at unprecedented scales. New technologies will emerge from these fundamental studies, including low-cost spectrometers, imaging and ranging, and energy harvesting and active cooling.

The project is led by ECE associate professor and physics affiliate professor Mikhail Kats as Principal Investigator, with Physics associate professor Victor Brar as one of the co-PIs.

Research Forward, a competition sponsored by the Office of the Vice Chancellor for Research and Graduate Education (OVCRGE), is intended to stimulate and support highly innovative and groundbreaking research at UW–Madison.

The initiative is supported by the Wisconsin Alumni Research Foundation (WARF) and will provide funding for 1–2 years, depending on the needs and scope of the project.

 

Smooth sailing for electrons in graphene

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two panels in heat-map style. both panels have circles in the middle. The panel on the left has more yellow and red to the left of the circle and a bright yellow ring around the circle; the right panel has a less sharp transition of colors from left to right and no bright ring around the circles.
A heatmap of electron location in graphene shows that at the lower temperature (left panel), the electrons are more likely to bump into impurities (circles), with relatively fewer making it through the channel between impurities. At higher temperatures (right panel), electron flow shifts to being fluid-like. Fewer are stuck at the impurities and more flow through the channels. UNIVERSITY OF WISCONSIN–MADISON

 

This story was originally published by University Communications

Physicists at the University of Wisconsin–Madison directly measured, for the first time at nanometer resolution, the fluid-like flow of electrons in graphene. The results, which will appear in the journal Science on Feb. 17, have applications in developing new, low-resistance materials, where electrical transport would be more efficient.

Graphene, an atom-thick sheet of carbon arranged in a honeycomb pattern, is an especially pure electrical conductor, making it an ideal material to study electron flow with very low resistance. Here, researchers intentionally added impurities at known distances and found that electron flow changes from gas-like to fluid-like as temperatures rise.

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Zach Krebs

“All conductive materials contain impurities and imperfections that block electron flow, which causes resistance. Historically, people have taken a low-resolution approach to identifying where resistance comes from,” says Zach Krebs, a physics graduate student at UW–Madison and co-lead author of the study. “In this study, we image how charge flows around an impurity and actually see how that impurity blocks current and causes resistance, which is something that hasn’t been done before to distinguish gas-like and fluid-like electron flow. 

The researchers intentionally introduced obstacles in the graphene, spaced at controlled distances and then applied a current across the sheet. Using a technique called scanning tunneling potentiomentry (STP), they measured the voltage with nanometer resolution at all points on the graphene, producing a 2D map of the electron flow pattern.

No matter the obstacle spacing, the drop in voltage through the channel was much lower at higher temp (77 kelvins) vs lower temp (4 K), indicating lower resistance with more electrons passing through.

At temperatures near absolute zero, electrons in graphene behave like a gas: they diffuse in all directions and are more likely to hit obstacles than they are to interact with each other. Resistance is higher, and electron flow is relatively inefficient. At higher temperatures — 77 K, or minus 196 C — the fluid-like behavior of electron flow means they are interacting with each other more than they are hitting obstacles, flowing like water between two rocks in the middle of a stream. It is as if the electrons are communicating information about the obstacle to each other and diverting around the rocks.

“We did a quantitative analysis [of the voltage map] and found that at the higher temperature, the resistance is much lower in the channel. The electrons were flowing more freely and fluid-like,” Krebs says. “Graphene is so clean that we’re forcing the electrons to interact with each other before they interact with anything else, and that is crucial in getting them to behave like a fluid.”

Former UW–Madison graduate student Wyatt Behn is a co-first author on this study conducted in physics professor Victor Brar’s group. Funding was provided by the U.S. Department of Energy (DE-SC00020313), the Office of Naval Research (N00014-20-1-2356) and the National Science Foundation (DMR-1653661).

Finding some wiggle room in semiconductor quantum computers

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a geometric pattern of lines in green, light gold, and black/dark purple, representing the qubit

Classical computers rarely make mistakes, thanks largely to the digital behavior of semiconductor transistors. They are either on or they’re off, corresponding to the ones and zeros of classical bits.

On the other hand, quantum bits, or qubits, can equal zero, one or an arbitrary mixture of the two, allowing quantum computers to solve certain calculations that exceed the capacity of any classical computer. One complication with qubits, however, is that they can occupy energy levels outside the computational one and zero. If those additional levels are too close to one or zero, errors are more likely to occur.

“In a classical computer, all the aspects of a transistor are super uniform,” says UW–Madison Distinguished Scientist Mark Friesen, an author on both papers. “Silicon qubits are in many ways like transistors, and we’ve gotten to the stage where we can control the qubit properties very well, except for one.”

That one property, known as the valley splitting, is the buffer between the computational one-zero energy levels and the additional energy levels, helping to reduce quantum computing errors.

In two papers published in Nature Communications in December, researchers from the University of Wisconsin–Madison, the University of New South Wales and TU-Delft showed that tweaking a qubit’s physical structure, known as a silicon quantum dot, creates sufficient valley splitting to reduce computing errors. The findings turn conventional wisdom on its head by showing that a less perfect silicon quantum dot can be beneficial.

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