2 Experiments Help Make Strange Metals Less Strange

By John Oncea, Editor

The behavior of so-called "strange metals" has long puzzled scientists — but two groups of researchers have shed some light on this mystery material.

NPR’s podcast The Academic Minute tells the story of Debanjan Chowdhury, assistant professor of physics at Cornell University, who wants to put an end to energy waste. “Chowdhury uses a variety of theoretical techniques to study and predict the quantum properties of trillions of interacting electrons in interesting materials, ranging from high-temperature superconductors to exotic magnets,” writes The Academic Minute.

In solid state physics, strange metals (also known as Planckian metals), are a metallic phase of matter which is not described well by Landau's Fermi liquid theory of small perturbations about the Fermi sea, explains nLab. “Known strange metals exhibit topological order in that their ground state has long-range entanglement (a topological phase of matter),” writes nLab. “Instead of by Fermi liquid theory, strange metals are well described by AdS/CFT in condensed matter physics.”

Chowdhury’s Strange Metals Solution

Chowdhury, whose work has been recognized by a CAREER award from the National Science Foundation and a Sloan research fellowship from the Alfred P. Sloan Foundation, says, “Imagine a world without an energy crisis, where limitless, clean, and inexpensive energy is available for all. One big challenge in realizing this dream is the loss of electricity during transmission from power plants to our homes. Scientists and engineers are trying hard to minimize this loss of energy; one approach uses a special class of materials known as high-temperature superconductors.”

Superconductivity is a fascinating example of how quantum mechanics can be observed in the real world. When a vast number of electrons work together in a coordinated manner, it results in the flow of electricity without any loss. However, the catch is that all known superconductors operate only at very low temperatures. Even the highest temperature superconductor has to be kept at minus 220 degrees Fahrenheit. The most well-known high-temperature superconductors belong to a family of compounds called cuprates.

“Despite decades of research,” says Chowdhury, “the microscopic reasons for why and how superconductivity emerges in cuprates remain largely unclear. We do know that when heated to higher temperatures, these materials lose their superconductivity, become metallic, and start showing other surprising properties.”

Chowdhury says in this metallic state the characteristic rate of electron collisions is universal and not governed by any property tied to the chemical composition of the material, suggesting that the possibility of a deeper connection between the strange metallic behavior and high-temperature superconductivity exists. “There are futuristic power plants where cuprate wires are being used in critical components,” continues Chowdhury. “Theoretical physicists need to keep working to understand the properties of strange metals as these could hold the key to using superconductivity at much higher temperatures – and could solve the problem of electricity loss in the future.”

Unusual Electrical Behavior, Insight Into The “Enigmatic Realm”

Chowdhury isn’t the only researcher looking into the wonders of strange metals. Two teams of researchers – one at the University of Toronto (go Blues!), the other a cooperative effort between the University of Cincinnati (go Bearcats!), the University of Hyogo, and RIKEN announced strange metal-related breakthroughs.

Let’s start with the University of Toronto which, according to Science Daily, “have developed a theoretical model describing the interactions between subatomic particles in non-Fermi liquids. The framework expands on existing models and will help researchers understand the behavior of these strange metals.”

“We know that the flow of a complex fluid like blood through arteries is much harder to understand than water through pipes,” says condensed matter physicist Arun Paramekanti, a professor in the U of T's Department of Physics in the Faculty of Arts & Science. “Similarly, the flow of electrons in non-Fermi liquids is much harder to study than that in simple metals.”

Lead author and physics Ph.D. student Andrew Hardy adds, “What we've done is construct a model, a tool, to study non-Fermi liquid behavior. And specifically, to deal with what happens when there is symmetry breaking, when there is a phase transition into a new type of system.

“Symmetry breaking in non-Fermi liquids is much more complicated to study because there isn't a comprehensive framework for working with non-Fermi liquids. Describing how this symmetry breaking occurs is hard to do.”

The implications of this research are far-reaching, particularly for the development of cutting-edge quantum technologies. For instance, high-temperature superconductors could soon become a reality, as they would be capable of achieving zero resistance at temperatures much closer to room temperature. This would make them far more practical and useful for everyday applications. Furthermore, graphene devices, which are based on ultra-thin layers of carbon atoms, offer a plethora of electronic applications.

The cooperative researchers, writes Science Daily, used a strange metal made from an alloy of ytterbium, a rare earth metal. Physicists fired radioactive gamma rays at it to observe its unusual electrical behavior and found unusual fluctuations in the strange metal's electrical charge.

“The idea is that in a metal, you have a sea of electrons moving in the background on a lattice of ions,” said the University of Hyogo and RIKEN’s Hisao Kobayashi. “But a marvelous thing happens with quantum mechanics. You can forget about the complications of the lattice of ions. Instead, they behave as if they are in a vacuum.”

“The thing that is exciting about these new results is that they provide a new insight into the inner machinery of the strange metal,” added study co-author Piers Coleman, a distinguished professor at Rutgers University. “These metals provide the canvas for new forms of electronic matter -- especially exotic and high-temperature superconductivity.”

Coleman said it's too soon to speculate about what new technologies strange metals might inspire but one day could be just as ubiquitous in our technology.