In an international collaboration involving experiments and theory, the topological wrapping of electrons in matter, which refers to the curvature of the space in which they exist and move, has been measured in a new class of materials. This new discovery could lead to a deeper understanding of quantum materials, which are materials where the collective behavior of the electrons that make them up generates new properties that can only be interpreted using the laws of quantum mechanics. These materials are expected to have future applications in various technological fields, from renewable energies to biomedicine, and from electronics to quantum computers. Using advanced experimental techniques that utilize light generated by a particle accelerator called a synchrotron, and thanks to modern modeling techniques of material behavior, it has been possible to measure the wrapping of electrons for the first time, in relation to the concept of topology. Just as a soccer ball and a donut have different topological properties related to their shapes (for example, the donut has a hole while the soccer ball does not), the behavior of electrons in materials is influenced by certain quantum properties that determine their wrapping, similar to how the trajectory of light in the universe is modified by the presence of stars, black holes, dark matter, and dark energy, which bend space and time. Although this particular characteristic of electrons has been known for many years, no one had been able to directly measure this “topological wrapping” until now. By exploiting an effect known as circular dichroism (from the Greek “di-” meaning two and “chroma” meaning color), which means that materials absorb light differently depending on its polarization, it has been possible to obtain this measurement for the first time. In addition to using this particular experimental technique available only at a synchrotron source, the synergy with theoretical analysis has been particularly relevant. In fact, the theoretical researchers on the team employed sophisticated quantum simulations made possible only through the use of powerful supercomputers, thus guiding the experimental colleagues towards the specific region of the material’s electronic properties where it was possible to measure the effect related to circular dichroism. Achieving this feat was the result of an international collaboration of scientists, including CNR-IOM in Trieste, the University of Bologna, Ca’ Foscari University in Venice, the University of Milan, the University of Würzburg (Germany), the University of St. Andrews (UK), Boston College, and the University of Santa Barbara (United States). The class of materials that the team focused on is called Kagome materials, named after their close resemblance to the pattern of bamboo threads in a traditional Japanese basket. These materials are revolutionizing quantum physics due to their magnetic, topological, and superconducting properties. This new discovery promises to revolutionize the way quantum materials will be studied in the future, thereby opening the doors to new developments in quantum technologies. The study has been published in the journal Nature Physics, D. Di Sante et al. “Flat band separation and robust spin Berry curvature in bilayer kagome metals.” The full article is available at the following link: https://www.nature.com/articles/s41567-023-02053-z

As part of the Engineering Physics colloquia monthly held at the Ca’ Foscari University of Venice, renowned researcher and former Italian minister Maria Chiara Carrozza was honoured with the “Emmy Noether Lecture Award” for her exceptional contributions to the fields of science, technology, and public service. Carrozza, currently serving as the President of the National Research Council of Italy (CNR), was recognized for her groundbreaking work and outstanding leadership in the pursuit of scientific advancements. The Emmy Noether Lecture Award is an accolade which will be presented yearly to individuals who have demonstrated exemplary achievements in the fields of physics and engineering, embodying the spirit of innovation, determination, and societal impact. Named after the pioneering German mathematician Emmy Noether, the award serves as a testament to the recipient’s outstanding intellectual contributions. Carrozza’s illustrious career spans both academia and public service, where she has consistently pushed the boundaries of scientific research while working tirelessly to translate her discoveries into tangible benefits for society. As the President of the CNR, she has played a pivotal role in fostering collaboration between academia, industry, and government to drive innovation and stimulate economic growth. Throughout her career, Carrozza has made significant breakthroughs in the field of robotics and assistive technologies, revolutionising the way we understand human-machine interactions and providing novel solutions to improve the quality of life for individuals with disabilities. Her research has paved the way for advancements in neuroprosthetics, wearable robotics, and rehabilitation engineering, earning her international recognition and acclaim. Carrozza’s exceptional leadership skills and passion for knowledge dissemination have also been instrumental in shaping science and technology policies at both national and international levels. Her previous role as the Italian Minister of Education, University, and Research allowed her to promote scientific literacy and establish strategic partnerships to foster interdisciplinary collaboration and innovation. Upon receiving the prestigious Emmy Noether Lecture Award, Carrozza expressed her deep gratitude and emphasised the importance of interdisciplinary research in addressing the complex challenges of our time. The ceremony at Ca’ Foscari University of Venice was attended by the Rector of the University Tiziana Lippiello, the Director of the Department of Molecular Sciences and Nanosystems Maurizio Selva and by the renowned physicist and SuperVenice member Guido Caldarelli, who gave a short lecture on the Noether’s theorem. The session was chaired by the coordinator of the Engineering Physics course Stefano Bonetti. Through a journey across her past activities in the world of science and technology, Carrozza emphasised the role of research institutions and universities in driving technological advancements and nurturing the next generation of innovators. The conferral of the Emmy Noether Lecture Award upon Maria Chiara Carrozza not only celebrates her remarkable achievements but also inspires aspiring female researchers and young minds to pursue scientific excellence and contribute to the betterment of society. Her commitment to pushing the boundaries of knowledge and harnessing technology for the greater good serves as an exemplary model for generations to come.

Real systems like our cities can have their digital versions, called “digital twins,” which are now possible due to the development in the fields of sensors and artificial intelligence. However, to transform these “doubles” from mere digital replicas to reliable tools for understanding the world and predicting behaviors, they need to be combined with the science of complexity. This is the key to creating cities that are genuinely human-centered. This is what a group of scientists, including Guido Caldarelli, a physicist at Ca’ Foscari University of Venice, argue in an article in Nature Computational Science. Digital twins are highly detailed replicas of real systems, including human bodies, cities, or the entire world, created by feeding representations of the elements of the respective system of interest into “black boxes.” This allows them to learn to behave more and more similarly to the corresponding elements of the real world. Digital twins can be used to study alternative scenarios and to control the real system based on artificial intelligence. However, “doubles” do not necessarily mean that digital twins behave realistically. Neither is there any advantage in creating a perfect copy of a system without understanding either the system or its simulation. Beyond issues related to big data and machine learning, local digital twins often oversimplify aspects such as social and cultural life and anything that is not represented by data. This includes everything that is immeasurable, such as friendships, love, and quality of life – things that are terribly important to humans but not to computer models, artificial intelligence, and robots. Therefore, Guido Caldarelli and his colleagues emphasize the need for digital twins to be combined with the science of complexity. This, they write, is the key to understanding global behaviors and not just a mere repetition inside the computer. The science of complex systems studies dynamic systems made up of many elements, which typically interact with each other or with other systems in a nonlinear way. Such systems often take the form of a network and can be layered several times, forming networks of networks. Taking interactions into account is essential for understanding the nature of complex systems, which cannot be understood solely from the properties of their individual parts. Nonlinear and network interactions are often the cause of emerging system properties. One can also speak of self-organization from the bottom up. Cities are full of these phenomena. They can range, for example, from the formation of uniform lines of walking directions on sidewalks to patterns of stopping and restarting traffic flows, or patterns of segregation between people with different cultural backgrounds, as Nobel Prize winner Thomas Schelling has shown. “As a consequence,” explains Guido Caldarelli, “digital twins not only need to consider the science of complexity to become useful and reliable tools. It is not even enough to plan, optimize, and control cities from the top down. To create cities for people, it is crucial to anticipate opportunities for self-organization, participation, and co-evolution.” Real systems like our cities can have their digital versions, called “digital twins,” which are now possible due to the development in the fields of sensors and artificial intelligence. However, to transform these “doubles” from mere digital replicas to reliable tools for understanding the world and predicting behaviors, they need to be combined with the science of complexity. This is the key to creating cities that are genuinely human-centered. This is what a group of scientists, including Guido Caldarelli, a physicist at Ca’ Foscari University of Venice, argue in an article in Nature Computational Science. Digital twins are highly detailed replicas of real systems, including human bodies, cities, or the entire world, created by feeding representations of the elements of the respective system of interest into “black boxes.” This allows them to learn to behave more and more similarly to the corresponding elements of the real world. Digital twins can be used to study alternative scenarios and to control the real system based on artificial intelligence. However, “doubles” do not necessarily mean that digital twins behave realistically. Neither is there any advantage in creating a perfect copy of a system without understanding either the system or its simulation. Beyond issues related to big data and machine learning, local digital twins often oversimplify aspects such as social and cultural life and anything that is not represented by data. This includes everything that is immeasurable, such as friendships, love, and quality of life – things that are terribly important to humans but not to computer models, artificial intelligence, and robots. Therefore, Guido Caldarelli and his colleagues emphasize the need for digital twins to be combined with the science of complexity. This, they write, is the key to understanding global behaviors and not just a mere repetition inside the computer. The science of complex systems studies dynamic systems made up of many elements, which typically interact with each other or with other systems in a nonlinear way. Such systems often take the form of a network and can be layered several times, forming networks of networks. Taking interactions into account is essential for understanding the nature of complex systems, which cannot be understood solely from the properties of their individual parts. Nonlinear and network interactions are often the cause of emerging system properties. One can also speak of self-organization from the bottom up. Cities are full of these phenomena. They can range, for example, from the formation of uniform lines of walking directions on sidewalks to patterns of stopping and restarting traffic flows, or patterns of segregation between people with different cultural backgrounds, as Nobel Prize winner Thomas Schelling has shown. “As a consequence,” explains Guido Caldarelli, “digital twins not only need to consider the science of complexity to become useful and reliable tools. It is not even enough to plan, optimize, and control cities from the top down. To create cities for people, it is crucial to anticipate opportunities for self-organization, participation, and co-evolution.” Link to the original article: https://www.nature.com/articles/s43588-023-00431-4

Starting April 1 st 2023, we are glad to host Tobia Arcangeli in our Statistical Mechanics Lab. Tobia is a student of Physical Engineering at Politecnico di Milano and will be working for his Master Degree within a joint project with his supervisor Prof. Roberto Piazza. The project will address a computational study of the phase behavior of a melt of semiflexible polymers, thus paving the way toward optimal experimental conditions for these systems.

To study what happens or could happen in extremely complex networks, such as in a pandemic or in Internet interactions, it is useful to simplify the system to make it manageable and to be able to analyze it. But how can one find the right vantage point to understand at a glance the salient features of the whole without losing sight of relevant connections? A team of physicists including Guido Caldarelli, corresponding author of the study and professor of theoretical physics at Ca’ Foscari University Venice, has found a method to efficiently and effectively ‘simplify’ the complex structure of the network. The result has been published in Nature Physics and is thus available to the international scientific community. The scholars took their cue from the technique that won U.S. physicist Kenneth G. Wilson a Nobel Prize in 1982. Wilson was able to find a theory that could explain how phase transitions, such as the freezing of the surface of a lake or the formation of a traffic column of cars, work. He invented the mathematical technique of the renormalization group, which allows one to exploit a symmetry of nature (large is similar to small) to predict the behavior of certain systems. Part of this method involves rescaling the cells in which the system is defined with larger and larger cells. At each step we merge both the cells of the system and the variables that make up the system (as in the figure where we have depicted a spin system). The knowledge of the system once the series of amalgamations is finished is able to tell us how the original system behaves at large distances and toward which fixed points the evolution of the system is headed. But how do we get the same advantage when the system is not made up of cells like a spreadsheet, but of nodes and relationships between them as is the case in our brains with neurons, in contagion between infected and susceptible individuals, or with interactions on social media? In real systems very often, if not always, interactions are characterized by the presence of a complex structure of connections that makes them very difficult to analyze. The knowledge of the system once we finish the series of unifications is able to tell us how the original system behaves at great distances and toward what fixed points the evolution of the system is headed. But how do we get the same advantage when the system is not made up of cells like a spreadsheet, but of nodes and relationships between them as is the case in our brains with neurons, in contagion between infected and susceptible individuals, or with interactions on social media? In real systems very often, if not always, interactions are characterized by the presence of a complex structure of connections that makes them very difficult to analyze. “Directly inspired by ideas from statistical physics,” Caldarelli explains, “we introduced a new renormalization group procedure that has proven essential for efficiently and elegantly discovering the organization at multiple scales of complex networks and for detecting scale invariant features when present. It also defines a universal network scaling procedure that is on the one hand very useful for analyzing large data sets and on the other hand shows us one of the fundamental symmetries of nature.” Future applications the team will work on include filtering of experimental data masses, exploration of material space, and representation of information from historical archives.

 A light wave at frequencies in the terahertz (from left) is converted into a spin wave (right) in a material made of thin metallic layers. An international research team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), of which Italian Stefano Bonetti, professor of materials physics at Ca’ Foscari University of Venice, is a member, has developed a new efficient method for making electromagnetic waves, such as those that enable our cell phones to communicate, interact with microscopic “spin waves,” or magnetic waves. As the experts report in Nature Physics, their experiment, in accordance with theoretical calculations presented in the same paper, elucidates the fundamental mechanism of this never-before-realized process. The results are an important step in the development of new, energy-saving, data-processing technologies based on magnetic materials. “The essence of the research,” Bonetti reports, “is that we were able to set off, inside a material, magnetic waves with wavelengths of a billionth of a meter and at very high frequencies (1,000 GHz, a thousand times faster than current processors). Theoretically, these waves can be used to transfer information into miniaturized electronic components at very high frequencies and low power consumption. The originality of these results is that the magnetic waves within the material were created using light with wavelengths a million times greater than the magnetic waves themselves. This is normally impossible: it would be like trying to pluck the string of a guitar with a pick a million times larger than the guitar itself. Instead, by creating a special ‘sandwich’ of very thin materials, we got around this problem, which was one of the main obstacles for this technology. Others remain, but it is a fundamental step forward, allowing us to create a bridge between the macroscopic world where we live, with the microscopic world of quantum physics.” Credits: HZDR/Juniks