Quantum materials were the focus for the 12th FAPESP 60 Years Conference, which featured leading experts in the field (image: screenshot taken during the event).
Published on 08/01/2022
José Tadeu Arantes | Agência FAPESP – Quantum physics is over 100 years old. It was founded in the early twentieth century by giants of science such as Max Planck, Albert Einstein, Louis de Broglie and Niels Bohr, and even now both basic research and technological applications in the field are flourishing.
One of the hotspots is what are known as quantum materials. Their investigation combines physics and engineering, materials science and quantum computing, superconductors and topological insulators, among other disciplines and areas. This subject of enormous theoretical and practical interest was discussed by participants in the latest FAPESP 60 Years Conference, the twelfth in a series of webinars held during 2022 to commemorate the São Paulo Research Foundation’s sixtieth anniversary.
The online event was opened by FAPESP President Marco Antonio Zago, who said quantum physics was a major paradigm shift and applications of quantum materials in everyday life are multiplying. The discussion was moderated by Marcelo Knobel, a professor at the State University of Campinas’s Gleb Wataghin Institute of Physics (IFGW-UNICAMP) and a former rector of the university.
Talks were delivered by the following scientists, listed in the order of presentation: Amir Ordacgi Caldeira, a professor of physics at UNICAMP and a member of the Brazilian Academy of Sciences since 2000; Adalberto Fazzio, a retired professor at the University of São Paulo's Institute of Physics (IFUSP), a former Rector of the Federal University of the ABC (UFABC), and currently head of Ilum Science School at the National Center for Research in Energy and Materials (CNPEM); and Sergio Machado Rezende, Emeritus Professor of Physics at the Federal University of Pernambuco (UFPE) and a former science and technology minister in the federal government of Brazil (2005-2010).
Caldeira’s presentation began with a brief history of quantum physics, highlighting the importance of the contributions to quantum computing made by Paul Benioff (1930-2022) and Richard Feynman (1918-1988).
“Reality is quantum,” he said. Quantum effects are hidden in the macroscopic experience of everyday life but visible in the behavior of molecules, atoms and sub-atomic objects, the collective properties of large collections of particles, such as superconductivity and superfluidity, and the exotic effects observed in new materials.
Caldeira then explained that the use of bits in conventional computing entails excitation or non-excitation of a physical object to encode data as zeros and ones, whereas quantum bits, or qubits, are associated with particle spin, which can be up or down or both at the same time.
The transition from conventional to quantum computing is therefore highly advantageous, as well as inevitable owing to increasing miniaturization of components. “The number of transistors in a typical microchip doubles every two years, and the elements are so small that they can no longer be governed by classical physics,” he said.
Quantum computing still faces the huge challenge posed by quantum systems’ loss of coherence to the environment, and this is one of the main focuses for research in the field, Caldeira concluded.
Fazzio’s talk revolved around the subject of topology in matter, a vast new field of research and applications. “Topology is a branch of mathematics dealing with the properties of objects that are invariant under smooth deformations,” he said.
Noting the advantages of topological insulators over trivial insulators, he cited an article recently published in the journal Science on a survey of 96,196 materials showing that 52.65% are topological.
Fazzio also discussed density functional theory (DFT), a quantum mechanical method used to describe the electronic structure of materials, especially topological insulators, and widely deployed in solid-state physics and chemistry to resolve complex molecular structures.
Turning to the advantages of quantum materials, Fazzio noted salient points from the Materials Genome Initiative launched in 2011 by President Barack Obama at Carnegie Mellon University: advanced materials have a wide array of applications and an almost infinite variability of projects in different agencies; they are studied and used by many knowledge areas; they are often product differentiators; and they are essential to economic progress and national security.
The main topic for Rezende, the last speaker in the webinar, was quantum material spintronics. Sub-atomic particles such as electrons have both electric charge and spin, an intrinsic form of angular momentum. Electronics uses charge, and spintronics deploys spin. “Particle spin occurs in one of two directions, either up or down, so it can be used as a carrier of information,” he said.
Rezende noted that Argentinian physicist Mario Baibich, who lives in Brazil and is a researcher at the Federal University of Rio Grande do Sul (UFRGS), was one of the pioneers of spintronics, with the study of a quantum mechanical effect called giant magnetoresistance (GMR), applied years later in computer hard disk read/write heads. The enhanced accuracy of GMR-based read heads led to an exponential increase in hard disk data storage capacity.
A more recently discovered phenomenon, according to Rezende, is spin current. “If spin-up and spin-down electrons travel in opposite directions, the charge current may be null, but the spin current will be different from zero and can transport information. However, in order to use spin current in a device we must somehow convert spin current into charge current,” he said. This is called the inverse spin Hall effect (ISHE).
Explaining that spintronics can be combined with electronics, he mentioned a study published in 2022 showing that a spin current can be “pumped” from a metallic material placed on a ferromagnetic material. The phenomenon is due to conservation of angular momentum. “This enables spin dynamics to be converted into spin current, and spin current can be manipulated,” he said.
Among recent applications of spintronics, Rezende cited random-access memory (RAM). “Conventional smartphone RAM isn’t everlasting but decays over time, whereas spintronics-based magnetic RAM never loses data,” he said.
A recording of the 12th FAPESP 60 Years Conference on quantum materials can be watched on Agência FAPESP’s YouTube channel at: https://www.youtube.com/watch?v=oph_eLaowuI.