Professors Luchang Jin and Tom Blum, along with colleagues at BNL and Columbia, Nagoya and Regensburg universities have completed a first-ever calculation of the hadronic light-by-light scattering contribution to the muon’s anomalous magnetic moment with all errors controlled. The work is published in Physical Review Letters as an Editor’s Suggestion and also appeared in Physics Magazine. A recent press release from Argonne National Lab described the calculation, which was performed on Mira, Argonne’s peta-scale supercomputer.
The team found the contribution is not sufficient to explain the longstanding difference between the Standard Model value of the anomalous magnetic moment and the BNL experiment that measured it. The discrepancy, which could indicate new physics, should be resolved soon by a new experiment at Fermilab (E989) and improved theory calculations, including the one described here, both with significantly reduced errors. E989 is set to release their first results later this year.
Medical imaging techniques such as MRIs use heavy metals from the bottom of the periodic table as “dyes” to make certain tissues easier to see. But these metals, called lanthanides, are toxic. To protect the person getting the MRI, some chemists wrap the lanthanide inside a cage of carbon atoms.
Molecular physicist Razib Obaid and his mentor, Prof. Nora Berrah in the physics department, wanted to know more about how the lanthanides interact with the carbon cages they’re wrapped in. The cages, 80 carbon atoms strong, are called fullerenes and are shaped like soccer balls. They don’t actually bond to the lanthanide; the metal floats inside the cage. There are many similar situations in nature. Proteins, for example, often have a metal hanging out close to a giant organic (that is, mostly made of carbon) molecule.
So Obaid and his team of collaborators from Kansas State University, Pulse Institute at Stanford, Max Planck Institute at Heidelberg, and the University of Heidelberg studied how three atoms of the lanthanide element holmium inside of an 80-carbon fullerene reacted to x-rays. Their initial guess was that when an x-ray first hit one of the holmium atoms, it would get absorbed by an electron. But that electron would be so energized by the absorbed x-ray thatit would fly right out of the atom, leaving a vacant spot. That spot would than get taken by another of the holmium’s electrons, which would have to jump down from the outer edge of the atom to fill it. That electron had formerly been partnered with another electron on the outskirts of the atom. When it jumped down, its lonely ex, called an Auger electron, would zoom away from the whole molecule and get detected by the scientists. Its distinctive energy would give it away.
It sounds complicated, but that would have been the simplest (and thus most likely) scenario, the physicists thought. But it’s not what they saw.
When Obaid and his colleagues zapped the holmium-fullerene molecule with a soft x-ray (about 160 electron-volts), the number of the Auger electrons detected was too low. And too many of the electrons had energies much less than the Auger electrons should have.
After some calculating, the team figured out there was more going on than they’d guessed.
First, the x-ray would hit the holmium, which would lose an electron. The vacant spot would then be filled by the outer edge electron from the holmium atom. That much was correct. But the energy released by the jumping electron (when it jumps ‘down’ from the outskirts of the atom to the interior, it also jumps ‘down’ in energy) would then be absorbed by the carbon fullerene cage or another of the neighboring holmium atoms. In either case, the energy would cause an additional electron to zoom away from whatever absorbed it, the fullerene cage or the holmium atom.
Losing these multiple electrons destabilized the whole molecule, which would then fall apart entirely.
The end result?
“You can induce radiation damage just by striking one atom out of 84,” says Obaid. That is, a single x-ray strike isenough to destroy the entire molecule complex through this energy transfer process involving neighboring atoms. It gives some insight into how radiation damage occurs in living systems, Obaid says. It was always thought that radiation damaged tissue by stripping away electrons directly. This experiment shows that interactions between an ionized atom or molecule and its neighbors can cause even more damage and decay than the original irradiation.
The work also gives medical physicists an idea of how to limit patient’s exposure to heavy metals used as dyes in medical imaging. Shielding all parts of the body from the radiation except for those to be imaged with heavy metal dyes can potentially restrict the heavy metal exposure as well as the radiation damage, the researchers say. The next step of this work would be to understand exactly how fast this interaction with the neighbors occurs. The researchers expect it to take place in just a few femtoseconds (10-15s).
The work was funded by Department of Energy, Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences, and Biosciences, under Grant No. DE-SC0012376.
Due to the current health situation and concerns surrounding the Corona virus, we are canceling the Katzenstein Lecture and Banquet scheduled for Friday, March 13, 2020.
It was an agonizing decision to cancel, but our first priority is the health of all who would have been attending, our special guest Professor Strickland, and the UConn community. I extend an extra apology for those of you who have planned to travel a considerable distance and will need to change plans. For those who have signed up for the banquet, we are working to arrange refunds.
If all goes well, the current health crisis will be behind us soon and we will see if we can reschedule Professor Strickland for another, safer time.
Again, my apologies and best wishes,
Barrett O. Wells
Professor and Head, Department of Physics
The University of Connecticut, Department of Physics, is proud to announce that on March 13, 2020, Professor Donna Strickland of the Department of Physics and Astronomy at the University of Waterloo will be presenting the 2020 Distinguished Katzenstein Lecture. Prof. Strickland is one of the recipients of the 2018 Nobel Prize in Physics for developing chirped pulse amplification with Gérard Mourou, her PhD supervisor. They published this Nobel-winning research in 1985 when Strickland was a PhD student at the University of Rochester in New York State. Together they paved the way toward the most intense laser pulses ever created. The research has several applications today in industry and medicine — including the cutting of a patient’s cornea in laser eye surgery, and the machining of small glass parts for use in cell phones.
Prof. Strickland earned a Bachelor in Engineering from McMaster University and a PhD in optics from the University of Rochester. She was a research associate at the National Research Council Canada, a physicist at Lawrence Livermore National Laboratory and a member of technical staff at Princeton University. In 1997, she joined the University of Waterloo, where her ultrafast laser group develops high-intensity laser systems for nonlinear optics investigations. She is a recipient of a Sloan Research Fellowship, the Ontario Premier’s Research Excellence Award and a Cottrell Scholar Award. She received the Rochester Distinguished Scholar Award and the Eastman Medal from the University of Rochester.
Prof. Strickland served as the president of the Optical Society (OSA) in 2013 and is a fellow of OSA, the Royal Society of Canada, and SPIE (International Society for Optics and Photonics). She is an honorary fellow of the Canadian Academy of Engineering as well as the Institute of Physics. She received the Golden Plate Award from the Academy of Achievement, is in the International Women’s Forum Hall of Fame, and holds numerous honorary doctorates.
The UConn Today published an article highlighting the state of 10-year renovation of the Gant Science Complex. The Complex was first constructed between 1974 and 1978 and was home to the departments of mathematics and physics for several decades. The renovation to this 285,00 square-foot campus landmark is part of Next Generation Connecticut, the initiative to expand educational opportunities, research, and innovation in the science, technology, engineering, and math (STEM) disciplines at UConn.
The Daily Campus published an article highlighting the research of Prof. Thomas Blum about Quantum Chromodynamics, a theory which describes the interactions between elementary particles. The development of this theory could help further understanding of the Standard Model of particle physics. The Standard Model is what physicists use to describe the fundamental building blocks of everything in the universe.
UConn Astrophysicist and observational astronomer Jonathan Trump was a recent guest on UConn 360, a podcast from the Storrs campus of the University of Connecticut. In this conversation, Jonathan tells about how attending a lecture as an undergraduate at Penn State captured his interest and changed the course of his professional career. Now Jonathan offers similar career-changing opportunities to UConn students, who just this year have applied for and obtained dedicated time for observations by the Hubble space telescope.
New building, new teaching approach, new people – there is a lot of change and excitement in the air for the Physics Department in 2019. The most obvious change is that physics has moved into a newly renovated building. What most alumni will remember as the Math Building has been taken down to its frame and rebuilt as the new physics building, formally Gant South. The new building features large windows with lots of light, revamped teaching labs, and a theory suite at the east end of each hallway. There are also plenty of meeting rooms and nooks, complete with writing spaces, to foster spontaneous discussions. We moved into the offices and teaching spaces at the start of fall semester, whereas the research lab relocations are ongoing as I write.
Along with the new building comes new teaching laboratories. The most striking of these are our studio-labs, located in the Gant Plaza building in the center of the Gant Complex. These studio labs have allowed us to redesign how we teach our introductory physics with calculus courses. Instead of three one-hour lectures per week and a three hour lab, there are now three two-hour meetings per week with mixed activities. The rooms are arranged with groups sitting around tables, and class time is spent on group efforts to explore concepts, solve problems, and conduct laboratory measurements. We have been developing this program using the Phys 1601 and 1602 courses for physics majors. This fall we rolled out the first of four other courses to be taught in this method with Phys 1501, to be followed in successive semesters by Phys 1502, Phys 1401, and Phys 1402.
If your travels bring you to the Storrs area, please stop by our new building. I will give anyone interested a tour myself if my schedule allows.
We also have several new faces around the department this fall. We have hired two new assistant professors in astrophysics, Chiara Mingarelli and Daniel Angles-Alcazar. Both have been hired in a bridge program with the Flatiron Institute of the Simons Foundation. Simons is the leading philanthropic foundation focused on science, and the four centers hosted at the Flatiron are world leaders in computational methods. We also have two new full-time teaching faculty, Niraj Ghimire and Sarah Trallero. Niraj was our own Ph.D. student who had previously worked on our Studio Physics development team. Sarah has been working with our teaching lab support team, with previous experience at Kansas State teaching studio-style physics courses. We have several new members of our teaching lab support team, with three new technicians. Zach Transport and James Jaconetta began working with us last January, and Hannah Morrill joined us over the summer. And finally, while I am not a new face, I took over as department head about a year ago and this is my first go-round writing a welcome to our newsletter. I would like to personally thank Professor Nora Berrah, our past department head, for putting our department on a firm footing that has made my job much easier.
Physicists used to think that superconductivity – electricity flowing without resistance or loss – was an all or nothing phenomenon. But new evidence suggests that, at least in copper oxide superconductors, it’s not so clear cut.
Superconductors have amazing properties, and in principle could be used to build loss-free transmission lines and magnetic trains that levitate above superconducting tracks. But most superconductors only work at temperatures close to absolute zero. This temperature, called the critical temperature, is often only a few degrees Kelvin and requires liquid helium to stay that cold, making such superconductors too expensive for most commercial uses. A few superconductors, however, have a much warmer critical temperature, closer to the temperature of liquid nitrogen (77K), which is much more affordable.
Many of these higher-temperature superconductors are based on a two-dimensional form of copper oxide.
“If we understood why copper oxide is a superconductor at such high temperatures, we might be able to synthesize a better one” that works closer to room temperature (293K), says UConn physicist Ilya Sochnikov.
Sochnikov and his colleagues at Rice University, Brookhaven National Lab and Yale recently figured out part of that puzzle, and they report theirresults in the latest issue ofNature.
Their discovery was about how electrons behave in copper oxide superconductors. Electrons are the particles that carry electric charge through our everyday electronics. When a bunch of electrons flow in the same direction, we call that an electric current. In a normal electric circuit, say the wiring in your house, electrons bump and jostle each other and the surrounding atoms as they flow. That wastes some energy, which leaves the circuit as heat. Over long distances, that wasted energy can really add up: long-distance transmission lines in the U.S. lose on average 5% of their electricity before reaching a consumer, according to the Energy Information Administration.
But in a superconductor below its critical temperature, electrons behave totally differently. Instead of bumping and jostling, they pair up and move in sync with the other electrons in a kind of wave. If electrons in a normal current are a rushing, uncoordinated mob, electrons in a superconductor are like dancing couples, gliding across the floor like people in a ballroom. It’s this friction-free dance – coherent motion – of paired electrons that makes a superconductor what it is.
The electrons are so happy in pairs in a superconductor that it takes a certain amount of energy to pull them apart. Physicists can measure this energy with an experiment that measures how big a voltage is needed to tear an electron away from its partner. They call it the ‘gap energy’. The gap energy disappears when the temperature rises above the critical temperature and the superconductor changes into an ordinary material. Physicists assumed this is because the electron pairs have broken up. And in classic, low-temperature superconductors, it’s pretty clear that that’s what’s happening.
But Sochnikov and his colleagues wanted to know whether this was really true for copper oxides. Copper oxides behave a little differently than classic superconductors. Even when the temperature rises well above the critical level, the energy gap persists for a while, diminishing gradually. It could be a clue as to what makes them different.
The researchers set up a version of the gap energy experiment to test this. They made a precise sandwich of two slices of copper oxide superconductor separated by a thin filling of electrical insulator. Each slice was just a few nanometers thick. The researchers then applied a voltage between them. Electrons began to tunnel from one slice of copper oxide to the other, creating a current.
By measuring the noise in that current, the researchers found that a significant number of the electrons seemed to be tunneling in pairs instead of singly, even above the critical temperature. Only about half the electrons tunneled in pairs, and this number dropped as the temperature rose, but it tapered off only gradually.
“Somehow they survive,” Sochnikov says, “they don’t break fully.” He and his colleagues are still not sure whether the paired states are the origin of the high-temperature superconductivity, or whether it’s a competing state that the superconductor has to win out over as the temperature falls. But either way, their discovery puts a constraint on how high temperature superconductors happen.
“Our results have profound implications for basic condensed matter physics theory,” says co-author Ivan Bozovic, group leader of the Oxide Molecular Beam Epitaxy Group in the Condensed Matter Physics and Materials Science Division at the U.S. Department of Energy’s Brookhaven National Laboratory and professor of applied physics at Yale University. Sochnikov agrees.
“There’s a thousand theories about copper oxide superconductors. This work allows us to narrow it down to a much smaller pool. Essentially, our results say that any theory has to pass a qualifying exam of explaining the existence of the observed electron pairs,” Sochnikov says. He and his collaborators at UConn, Rice University, and Brookhaven National Laboratory plan to tackle the remaining open questions by designing even more precise materials and experiments.
The research work at UConn was funded by the State of Connecticut through laboratory startup funds.
August 19, 2019 – Anna Zarra Aldrich ’20 (CLAS), Office of the Vice President for Research
When Carlos Trallero started his academic career in physics, he had no idea he would become a pioneer in a field of research that uses high-power lasers to investigate atomic and molecular physical phenomena.
Originally from Cuba, where there isn’t much funding for experimental research, Trallero began his academic career by studying theoretical physics. But as a senior graduate student at Stony Brook University, he got the chance to work in a lab doing experimental work and quickly recognized it was his true passion.
“I talked to a professor doing experimentation with ultra-fast lasers and I fell in love with it. And at first, I sucked at it — I was horrible,” says the professor of physics who is now working with four research grants funding separate investigations.
Trallero works with very short laser beams, with an emphasis onvery short. The lasers he uses can pulse with attosecond precision. As a comparison, there are as many attoseconds in one second as there have been seconds in the entire history of the universe since the Big Bang.
It takes light half an attosecond to cross the orbit of hydrogen, the smallest atom. When trying to study something that fast, scientists need the kind of precision the lasers Trallero can offer. The goal of this research is to gain a better understanding of how electrons, one of the fundamental atomic building blocks in the universe, move and react to light. By understanding the physics of electron movement, scientists could improve the design of technologies like superconductors.
“The dream is to be able to perform logistical operations like a computer at the attosecond level,” Trallero says. “It would really advance computational speeds. If you could make as many calculations in a second as there have been seconds in the history of the universe – that’s an astounding number.”
His lab is now working to break the attosecond barrier into the zeptosecond barrier which is 1,000 times faster than the attosecond.
While some of the potential applications of this research remain unknown since the field is still in its infancy, Trallero views the premise of his research as creating basic knowledge. He is investigating the atomic and molecular phenomena which determine so many things in our universe but about which we still know relatively little.
One project funded by the Department of Energy has Trallero looking at the properties of atoms and molecules in the quantum world by harnessing light waveforms at the attosecond time scale through interferometry. Interferometers provide precise measurements of molecules using two beams of light which interfere with each other. The images produced by this technology will allow Trallero to find out information about the rotational dynamics of molecules.
“In the quantum world, properties of atoms and molecules are not as simple as in the real world,” says Trallero.
Another of Trallero’s grants, from the U.S. Air Force Office of Scientific Research, involves creating an incredibly bright beam. Trallero’s lab is working on taking electrons out of nanoparticles and then sending them back in, which will produce a bright, energetic light. “The process to study these dynamics has never been executed in this manner,” Trallero says.
Trallero is also working on two grants from the U.S. Navy, including one that aims to develop infrared “body heat lasers.”
Through these grants, Trallero is developing a new class of laser which is only comparable to those found at large, multinational laser facilities like the European Light Infrastructure. Compared to the technology currently available to Trallero at UConn, this new class of laser will have almost 20 times more average power than the current laser.
Developing a laser of this caliber will be incredibly useful for studying phenomena that only occur a few times per shot of the laser in real time. The laser will enable researchers to probe the molecules with X-rays and ultraviolet rays to look at their structure and is being developed through a partnership with a Canadian company, Few-cycle, and a German company, Amphos. Researchers like Trallero are able to get advanced technology for a fraction of their retail value by doing research of interest for these companies, which are constantly trying to innovate in step with the science.
“We’re only paying a fraction of the price because the company is interested in showing they can develop this kind of technology,” Trallero says. “Showing they have the capacity and showcasing what we do with, and for, them helps them gain a customer base and it helps us make major advances in basic science at the same time.”
Trallero is also considering creating spin-off tech companies based on his university inventions with graduate students and postdocs. He has developed nanoparticle technology which can help transform molecules from a liquid to a gaseous state which could be beneficial for producing aerosols.
Trallero views physics as “the broadest science” since it has unique applications to math, engineering, chemistry and, even, biology. “I try to think about particular scientific questions in a different way than perhaps other people who have been working in this field for a long time do,” Trallero says. “Often we suffer from too much in-depth specialization.”
He wants to make use of the tools from every specialty he can, and he instills this same inclination in the students working in his lab.
“They don’t know what they’re going to face in the future and by having a broad skill set and a broad mindset they’ll be prepared for anything,” Trallero says. “You’re opening your mind to more possibilities.”
Amelia Henkel, graduating Double Major in Physics and Human Rights, and President of the Undergraduate Women in Physics Club, speaks on the CLAS website about her passion for physics and human rights, and how she mastered challenges in her remarkably interdisciplinary curriculum. “We really need to interact with other disciplines,” says Amelia, “because that’s when physics has the opportunity to make a real impact on the rest of the world.” Her broad research interests range from A to W: from Astronomy to Women’s, Gender, and Sexuality Studies. “Respecting and promoting human rights is a prerequisite to realizing our full potential as human beings,” says Amelia. Physics as a discipline has made progress to become more inclusive, but many groups remain minorities including women. In daily college life in physics departments female students still face “microaggressions and discriminatory practices” which are often unintended and unconscious but nonetheless damaging and frustrating. As the President of the Undergraduate Women in Physics Club, Amelia helped to organize “events that promote community cohesion and inform the students about the nature of some of the barriers that exist in physics and in STEM, while talking about how we can overcome them.” The recent department-wide event Women in Physics Colloquium organized by Amelia was thought provoking and well-received. The percentage of women earning a Bacheleor’s Degree in Physics from UConn, though slowly increasing and compatible with the national average of about 20% published by APS, is far away from where we wish to be. But the efforts of students like Amelia contribute to improving the situation. Many thanks to Amelia whose commitment helps to make our department better.
Read more about Amelia on the CLAS website. A short summary of her story is in UConn Today.