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Topological defects in 3D simulated glasses: new paper in Nature Communications

Geometry and topology play a central role in modern physics, from the formation of cosmic strings in the early universe to the intricate growth patterns of leaves and rose petals. From an applied perspective, topological defects are key to understanding mechanical failure in solid materials and to describing melting phenomena in two-dimensional systems.

Defining defects, however, requires a reference configuration, typically an idealized ordered background. In crystals, atoms are arranged in periodic lattice structures, breaking continuous translational symmetry down to a discrete subgroup. This ordered background allows for a precise definition of defects such as dislocations and disclinations.

In contrast, amorphous materials, like the glass in a window, lack long-range order. Atomic arrangements are disordered beyond a few interatomic distances, making the identification and classification of defects particularly elusive. Yet this is not merely an academic challenge: the ability to predict where and how a glass might fail under stress has direct implications for material design, safety, and engineering.

In recent years, significant progress has been made in identifying topological defects in glasses. However, these developments have largely been confined to simplified two-dimensional models, limiting their relevance to real-world materials. In a recent Nature Communications publication, Professor Matteo Baggioli (SJTU), in collaboration with Professor Alessio Zaccone (University of Milan) and Dr. Arabinda Bera, introduced, for the first time, a robust definition of topological defects in three-dimensional glasses.

Their approach draws on the concept of topological hedgehog defects, a playful reference to the small creatures often seen on SJTU’s campus at night. Crucially, the study shows that in three dimensions, topology alone is not sufficient. The geometry of the defect, particularly the spatial configuration around its core, becomes essential. In particular, the team finds that regions prone to plastic deformation and mechanical failure are associated with hyperbolic-shaped hedgehog defects, structures that inherently feature unstable directions.

This work provides a mathematically well-defined, physically grounded framework for identifying defects in realistic three-dimensional amorphous materials. It opens new avenues for understanding failure mechanisms in glasses and offers promising applications across physics, materials science, and engineering.

The work is published in Nature Communications, Hedgehog topological defects in 3D amorphous solids | Nature Communications

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Topological defects in 2D glasses: new paper in Nature Communications!!

First experimental observation of topological defects in glasses

The amorphous (disordered) state of matter represents the largest quote of visible matter in the universe and includes all biological systems such as the cells which form the human body, or essential materials for mankind such as glass and polymers. The relevance of structurally disordered systems has further implications for artificial intelligence, the nervous system of living beings and even the large-scale structure of the cosmos. In all these disordered systems, it is impossible to identify any kind of periodicity or regular pattern. In the opposite case of a crystal, where atoms occupy regular, and well-defined, positions in space, the mathematical description is much facilitated not only thanks to the crystallographic order but also thanks to easily identifiable “defects” which practically control the physical properties of the crystal, such as its plastic yielding and melting, or the way an electric current propagates through it. Of particular importance are the topological defects, mathematically described as points of singularity within an ordered pattern, and around which the integral of a certain quantity changes its value after a full loop around the defect. Well known examples of topological defects are vortices and anti-vortices in superfluids, and dislocations in crystals, which control the mechanical properties thereof.

In strongly disordered systems such as glasses, instead, in spite of many speculations about the existence of topological defects dating back at least to the 1970s, a direct observation in a real system has been lacking so far. A first breakthrough came in 2021, when mathematically well-defined topological defects were defined and observed for the first time in computer simulations of glassy materials [Phys. Rev. Lett.127, 01550, 2021]. In 2023, an independent study [Nature Communications volume 14, Article number: 2955 (2023)] confirmed the validity of this idea and generalized it to the topology of vibrational modes, revealing a strong correlation with plasticity in simulated glasses.

Figure 1: A snapshot of the experimental 2D colloidal system used in Nature Communications volume 16, Article number: 55 (2025). The overlapped inset shows the structures of one vibrational mode with the topological defects indicated with red and blue disks accordingly to their positive/negative topological charge.

Now, thanks to particular methods of numerical analysis applied to the treatment of experimental data from confocal microscopy, it has been possible to clearly identify the topological defects in a colloidal glass experimentally realized by randomly assembling colloidal particles that interact via a magnetic field (see Figure 1). The material presents the same random structure and properties as any other glass. The experimental data were produced at the Max Planck Institute in Goettingen (Germany) in the lab of Prof. Peter Keim, and the theoretical analysis was performed by Prof. Matteo Baggioli (SJTU) in collaboration with Prof. Alessio Zaccone team (University of Milano).

The experimental demonstration of the existence of topological defects in disordered systems is a turning point in condensed matter physics because it paves the way to the possibility of rationally controlling and manipulating the physical properties of all the above-mentioned materials and systems, something which was not possible so far.

This study was published in Nature Communications volume 16, Article number: 55 (2025).

Professor Matteo Baggioli (Wilczek Quantum Center, School of Physics and Astronomy, Shanghai Jiao Tong University) is one of the corresponding authors.

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Vibrational anomalies and stringlets in active glasses: new PRL paper

Recently, the Soft Matter and Active Matter Collaborative Research Group of Shanghai Jiao Tong University (Matteo Baggioli Group of Wilczek Quantum Center and Jie Zhang Group of Institute of Natural Sciences / School of Physics and Astronomy) made important progress in the study of local vibration of active particulate matter. Based on the experiment of active Brownian particle system, the research group confirmed the local vibration of strings, and its corresponding zero group velocity dispersion relation predicted two years ago. This study is of great significance for understanding the singularity of the intrinsic vibration of amorphous solids, which is a mystery left to be solved in the last century.

Phys. Rev. Lett. 133, 188302 (2024) – Dispersionless Flat Mode and Vibrational Anomaly in Active Brownian Vibrators Induced by Stringlike Dynamical Defects

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We are on the cover of ACS NANO!

Our article was published in ACS NANO and features on the cover of the September issue! Congratulations to Yuanxi, Sha and Xue, great work!!

Emergence of Debye Scaling in the Density of States of Liquids under Nanoconfinement | ACS Nano

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Xu Yang joined our group as a master student!

Xu Yang (许阳) joined our TheoryLab group as a master student ad he will do research on soft matter theory. Welcome to the group Xu !!!

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Twisting bilayer graphene in a chiral optical cavity: new PRL

The twisted bilayer graphene (TBG) system is one of the important discoveries in condensed matter physics in recent years. It has become an extremely rich platform for studying quantum many-body physics. Especially at a specific twist angle, the so-called “magic angle” (approximately 1.05 degrees), TBG undergoes a superconducting phase transition. Although the origin of exotic superconductivity in TBG remains a controversial topic, it is generally believed that the flat-band effect plays an essential role. However, since TBG is not a stable configuration at the magic angle, it is often difficult to accurately prepare magic-angle graphene experimentally. Experiments have observed that when the twist angle deviates from the magic angle by 0.1 degrees, the superconducting phase disappears. This instability has limited extensive research on superconducting properties in TBG. 

In this study, the researchers proposed a new method, namely, using quantum fluctuations in a chiral microcavity to engineer the band structure of TBG, so that TBG can form a flat band beyond the magic angle. The physical picture is that the chiral microcavity breaks time-reversal symmetry, and the vacuum quantum fluctuations in the cavity inherit the characteristics of time-reversal symmetry breaking. The time-reversal symmetry broken quantum fluctuations can induce energy gaps in the band structure, leading to a significant impact on the band flatness near the magic angle. By controlling the effective mode volume of the chiral microcavity, one can effectively tune the coupling strength of electron-photon interaction, achieving precise control of the band structure and even topological properties of the system. This work is based on the previous studies on the quantum atmospheric effect and the chiral vacuum molecule selection effect.

Cunyuan Jiang, Matteo Baggioli, and Qing-Dong Jiang, Phys. Rev. Lett. 132,  166901 (2024)

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New member in our group, welcome Jimin!

Jimin joined our group as a PhD student, welcome to the gang!!

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New member in our group, welcome Bowen!

Bowen Ouyang (欧阳博文) joined our TheoryLab group as an undergraduate student working on applied holography! Welcome Bowen!

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A time crystal in a black hole, new PRL paper

Can we make a system that breaks time-translations spontaneously — a time crystal — as an ordinary crystal does with spatial translations? Yes!

Can we make this time crystal holographic and embed it in a gravitational solution with a black hole? Yes!

Check our new PRL work: Phys. Rev. Lett. 131, 221601

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New member in the group, welcome Peng Yang

Peng Yang will join our research team in September 2023, welcome to the group!!!