UMD Alumnus Wins Breakthrough New Horizons Prize

Aron Wall, who received his UMD Ph.D. in 2011, has been awarded the 2019 Breakthrough New Horizons in Physics Prize for fundamental insights about quantum information, quantum field theory and gravity. The $100,000 prize is given each year to up to three “promising junior researchers who have already produced important work.” In addition to the Breakthrough Prize, Wall has also recently received the Philippe Meyer Prize in Theoretical Physics and the Young Scientist Prize for the International Commission on General Relativity & Gravitation.

Wall’s UMD dissertation was awarded the Bergmann-Wheeler Thesis Prize, given every three years by the International Society on General Relativity and Gravitation. Distinguished University Professor Ted Jacobson was Wall’s advisor.

After completing his doctorate, Wall held positions at the University of California at Santa Barbara, the Institute for Advanced Study and the Stanford Institute for Theoretical Physics. In January, he will join the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge.

Fast-flowing electrons may mimic astrophysical dynamos

dynamo galitski1 blue galleryCertain materials may host an electron fluid that flows fast enough to generate turbulence and bootstrap a dynamo. (Credit: E. Edwards/JQI)

A powerful engine roils deep beneath our feet, converting energy in the Earth’s core into magnetic fields that shield us from the solar wind. Similar engines drive the magnetic activity of the sun, other stars and even other planets—all of which create magnetic fields that reinforce themselves and feed back into the engines to keep them running.

Much about these engines, which scientists refer to as dynamos, remains unknown. That’s partly because the math behind them is doubly difficult, combining the complex equations of fluid motion with the equations that govern how electric and magnetic fields bend, twist, interact and propagate. But it’s also because lab-bound dynamos, which attempt to mimic the astrophysical versions, are expensive, dangerous and do not yet reliably produce the signature self-sustaining magnetic fields of real dynamos.

Now, Victor Galitski, a Fellow of the Joint Quantum Institute (JQI), in collaboration with two other scientists, has proposed a radical new approach to studying dynamos, one that could be simpler and safer. The proposal, which was published Oct. 25 in Physical Review Letters, suggests harnessing the electrons in a centimeter-sized chunk of solid matter to emulate the fluid flows in ordinary dynamos.

If such an experiment is successful, it might be possible for researchers in the future to study the Earth’s dynamo more closely—and maybe even learn more about the magnetic field flips that happen every 100,000 years or so. "The dynamics of the Earth’s dynamo are not well understood, and neither are the dynamics of these flips," says Galitski, who is also a physics professor at the University of Maryland. "If we had experiments that could reproduce some aspects of that dynamo, that would be very important."

Such experiments wouldn’t be possible but for the fact that electrons, which carry current through a material, can sometimes be thought of as a fluid. They flow from high potential to low potential, just like water down a hill, and they can flow at different speeds. The trick to spotting the dynamo effect in an electron fluid is getting them to flow fast enough without melting the material.

"People haven’t really thought about doing these experiments in solids with electron fluids," Galitski says. "In this work we don’t imagine having a huge system, but we do think it’s possible to induce very fast flows."

Those fast flows would be interesting in their own right, Galitski says, but they are especially important for realizing the dynamo effect in the lab. Despite the many lingering unknowns about dynamos, it seems that turbulence plays a crucial role in their creation. This is likely because turbulence, which leads to chaotic fluid motion, can jostle the magnetic field loose from the rest of the fluid, causing it to twist and bend on top of itself and increase its strength.

But turbulence only arises for very fast flows—like the air rushing over the wing of an airplane—or for flows over very large scales—like the liquid metal in the Earth’s core or the plasma shell of the sun. To create a dynamo using a small piece of solid matter, the electrons would need to move at speeds never before seen, even in materials known for having highly mobile electrons.

Galitski and his collaborators think that a material called a Weyl semimetal may be able to host an electron fluid flowing at more than a kilometer per second—potentially fast enough to generate the turbulence necessary to bootstrap a dynamo. These materials have received broad attention in recent years due to their unusual characteristics, including anomalous currents that arise in the presence of magnetic fields and that may reduce the speed required for turbulence to emerge.

"It might seem that turbulence isn’t particularly extraordinary," says Sergey Syzranov, a co-author and former JQI postdoctoral researcher who is now an assistant professor of physics at the University of California, Santa Cruz. "But in solids it has never been demonstrated to our knowledge. A major achievement of our work is that turbulence is realistic in some solid-state materials."

The authors say that it’s not yet clear how best to kickstart a dynamo on a small sliver of Weyl semimetal. It may be as simple as physically rotating the material. Or it could require pulsing an electric or magnetic field. Either way, Galitski says, the experimental signature would show a totally nonmagnetic system spontaneously form a magnetic field. "Controlled experiments like these with turbulence in electrons are totally unheard of," Galitski says. "I can’t really say what will come out of it, but it could be really interesting."

Mehdi Kargarian, a former JQI postdoctoral researcher who is now an assistant professor of physics at the Sharif University of Technology, was also a co-author of the new paper.

Story by Chris Cesare

Read more information on this and the Joint Quantum Institute.

Manuel Franco Sevilla Joins UMD Physics

Manuel Franco Sevilla installs ODMB modules into the CMS detector at CERN. (Photo: Jeff Richman)

Manuel Franco Sevilla has joined the Department of Physics as an assistant professor. He recently completed a postdoctoral appointment at the University of California at Santa Barbara.

Franco Sevilla received his Ph.D. in experimental particle physics at Stanford University, working on the BaBar experiment at the SLAC National Accelerator Laboratory. At SLAC he did seminal work on lepton universality, a fundamental assumption within the Standard Model (SM) of particle physics that states that the interactions of all charged leptons differ only because of their different masses. Franco Sevilla’s work challenges this assumption and helped launch a new area of studies in the experimental programs at the CERN Large Hadron Collider (LHC) and B factories, stimulating many possible interpretations based on physics beyond the SM.

As a postdoctoral researcher, Dr. Franco Sevilla moved to the Compact Muon Solenoid (CMS) experiment at the LHC, where he made major contributions both to the development of particle detector instruments as well as to the physics analysis of the data in the area of Supersymmetry. In 2014 he was recognized with a CMS Achievement Award for “outstanding design and construction of the 72 Optical Data MotherBoards (ODMB) that control and read out” the complex electronics needed in this part of the operation, and during 2016-2018 he was appointed Coordinator of the CMS Cathode Strip Chambers (CSCs) upgrade for the high luminosity LHC and Deputy Project Manager of the CSC group.

He now joins the LHCb experiment at CERN and looks forward to continuing his research on lepton universality violation and engaging students in the study of today’s open questions in fundamental physics. Additionally, he will contribute to the development of the electronics for a new tracker detector to be installed in LHCb in 2020.

 MFS CERN 2smManuel Franco Sevilla installs ODMB modules into the CMS detector at CERN. (Photo credit: Jeff Richman)