Quantum Materials and the 85-Year-Old Prediction: Inside the 27th Science Cafe

The 27th Science Cafe was held on Wednesday, July 30, in Tehran, featuring a talk by Mehdi Kargarian, associate professor of physics at Sharif University of Technology. Speaking to an audience of students and science enthusiasts, Kargarian discussed key concepts in quantum physics and the properties of topological materials in the context of Mohammad Zahid Hasan’s groundbreaking research, which earned him the Mustafa(pbuh) Prize in 2021.
MSTF Media reports:
The 27th Science Cafe was held on Wednesday, July 30, at a cafe in Tehran, with the presence of Mehdi Kargarian, an associate professor in the Faculty of Physics at Sharif University of Technology, and a number of students and science enthusiasts.
In the event, the nature and essence of quantum physics and topological particles were discussed and the achievements of Mohammad Zahid Hasan, a Bangladeshi-born scientist based in the US and a winner of the Mustafa(pbuh) Prize.
Kargarian opened this event with an introduction on the history of physics, explaining that physicists seek to understand natural phenomena for two reasons: to satisfy their sense of curiosity and to advance life with the help of nature (and later technology). More importantly, he said, if we understand a law in nature, we can overcome it.
"By the late 17th century, mankind had come up with a good formulation of all phenomena, which are called Newton’s Laws. Also, in the 19th century, James Clerk Maxwell provided a comprehensive explanation of the laws of electromagnetism and optics?. The laws of thermodynamics (the relations between heat and other forms of energy) were also theorized because of the importance of this field in the Industrial Age.
According to Kargarian, in the late 19th century, any phenomena in the natural world could be explained through these laws. In the early 20th century, however, a couple of observations showed that these theories were not sufficient. For example, scientists had already noticed that atoms, as tiny particles of matter, are unstable, but no law in classical physics could explain their instability. Also, a phenomenon called “blackbody radiation” and the distribution of energy in this body were incompatible with any other phenomenon in classical physics.
Where Did Quantum Come From?
As a result of these incongruities, Kargarian maintained, it was decided that there was a need to reconsider the theories in physics. Max Planck, who discovered the blackbody radiation in the early 20th century, concluded that radiation in a blackbody is discrete and that if he replaces a continuous factor with a discrete factor in his formulas, he will arrive at quantum. Before this, everything that was known in physics was continuity. Therefore, quantum mechanics first began with crude assumptions and by adding the discontinuity theory, and gradually reached a new formulation.
Kargarian then carried out a few simple, hands-on experiments with a Mobius Strip—a rectangular strip with two ends which are attached with a half-twist. He introduced topological materials and topological order, demonstrating that in topological systems, all components are intertwined: if an operation is performed on one part, the entire system collapses.
He then talked about magnets and magnetic fields, which he said are “the basis for building information storage devices such as different types of computers and memories.” He also explained the concept of binary digits (zeros and ones), saying that in topological quantum computers, although individual bits might appear similar locally, their overall system state differs, allowing for more stable and better computers in terms of processing.
Who is M. Zahid Hasan?
Kargarian continued by giving a brief account of Zahid Hasan’s life and his achievements. The Mustafa(pbuh) Prize laureate was born in Bangladesh, where he lived until 1990. After immigrating to the US, he continued his studies at the University of Austin, and then Stanford University, where he received his doctorate in 2002.
Regarding Hasan’s scientific achievements as a quantum physics scientist, Kargarian said, humanity's view of the world of materials is important, but in the history of physics, materials have usually been discovered by chance or pure luck; however, over the last decade or two, the prevailing view of the discipline has changed and most scientists are willing to predict what new materials are possible to be discovered or to first design the desired states of materials on paper and then give the instructions to the laboratory to make the materials. Some superconducting materials (materials with zero resistance to electric current) or topological insulators were discovered in this way, and some of these materials were discovered by Zahid Hasan and his research group in 2015 and 2016.
The Sharif University professor pointed out that the importance of Zahid Hasan's work is that he used Mendeleev's periodic table, finding materials that both confirmed the predictions of previous theories while raising new questions about materials that were later answered by scientists active in the theoretical area.
He then talked about the Weyl semimetals pointing out that they were first addressed by the German physicist, Hermann Weyl, in 1929. In the first decades of the invention of quantum mechanics, researchers were interested in atoms, particle physics, and the interior of the nucleus. Because the energy inside the nucleus is very high, they had to combine quantum mechanics with relativity to understand these processes, which was what the English physicist Paul Dirac did. One of the results of the Dirac equation was that it predicted particles in nature that have chirality or handedness (they are either right-handed or left-handed). But these particles were never discovered in nature and were thought not to exist at all.
Despite this, in 2015, Hasan introduced a material called sodium bismuthate which was similar to Weyl semimetals. His next important discovery was another matter whose electrons' energy is like Weyl semimetals and is chiral, that is, some spots of the electrons are either right-handed or left-handed. His discovery is not just a particle in nature; what Hasan and his team discovered has indeed been theoretically predicted 85 years ago. From a materials science perspective, these materials have conductivity comparable to magnetic materials, and their electrons do not accelerate in the direction of the magnetic field.
Science Cafe is a conversation-based event by the Mustafa(pbuh) Science and Technology Foundation Observatory, which aims at explaining scientific topics and concepts in an accessible language and in a public environment. Since 2022, regular Science Cafe sessions have been held in such cities as Tehran, Tabriz, Isfahan, Zanjan, and Pardis.