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Stay informed with our latest news and announcements on this page. For more in-depth content, we also encourage visitors to explore our bimonthly STRUCTURES Newsletter magazine, which features a variety of articles, interviews with members, and background information on our latest research and activities.
Biological cells are the smallest living units of an organism. To maintain their shape, divide, and move, they rely on the cytoskeleton, which is made from biopolymers like actin. Actin assembles into filaments and larger networks, which constantly undergo renewal, as monomers are added, removed, and re-used elsewhere. This dynamic behaviour allows the cell to rapidly adapt to changing environmental conditions. At the same time, this poses a problem: the different actin structures compete for a shared limited pool of free actin monomers. If one structure consumes more, less remains for the others, causing them to shrink, as they lose actin faster than they can replace it. Yet, one observes that multiple distinct structures can coexist at stable sizes. This raises the question of which mechanism prevents single structures from monopolizing the shared pool.
In a new study, STRUCTURES scientists Valentin Wössner, Falko Ziebert and Ulrich Schwarz have made substantial progress in solving this puzzle. They developed a theory for coexistence and selection of branched actin networks – going beyond earlier models that had focused mainly on single filaments and bundles. Using ordinary differential equations (ODEs) and bifurcation analysis, their framework shows how local depletion of actin can provide a natural self-regulating mechanism: as a dense network grows, it uses up the free actin at its leading edge, slowing its own further growth. When competition becomes too strong, coexistence gets replaced by selection. The new theory bridges so-called limited pool models and the growth physics of branched actin networks.
Methodological exchange between the disciplines of biophysics and scientific computing proved crucial for validating this result. In addition to analytical modelling, the researchers solved partial differential equations (PDEs) describing the spatial distribution of actin to confirm their predictions in greater detail for selected cases. These simulations were carried out using a module of the numerical software framework DUNE – which has been co-developed by STRUCTURES member Peter Bastian. The close agreement found between both approaches supports the ODE model as an effective description of the dynamics.
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Valentin Wössner is a doctoral researcher at the Institute for Theoretical Physics (ITP) and at BioQuant, and a member of the STRUCTURES Young Researchers Convent (YRC). Ulrich Schwarz is Professor of Theoretical Physics at the Institute for Theoretical Physics (ITP) and BioQuant, and a Principal Investigator in STRUCTURES' Comprehensive Project CP3 (From Molecules to Cells and Tissue). Falko Ziebert is a Privatdozent at the Institute for Theoretical Physics (ITP) and a full member of STRUCTURES. Peter Bastian is a Professor of Scientific Computing at the Interdisciplinary Center for Scientific Computing (IWR) and also a Principal Investigator in CP3 of STRUCTURES.
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Quantum Gases of Light Exhibit Critical Scaling Behaviour – Major Research Gap in the Physics of Phase Transitions Closed
An international team of researchers including STRUCTURES member Julian Schmitt has studied the critical behaviour of photons close to a phase transition. The researchers have demonstrated the phenomenon of critical scaling behaviour in a quantum gas of photons for the first time. The result has been published in Science Advances.
A team of researchers from the University of Bonn, Heidelberg University and the National Autonomous University of Mexico has studied the critical behaviour of light particles (photons) close to a phase transition. This critical scaling behaviour, which sees thermodynamic quantities grow extremely large or diverge near phase transitions, had never before been seen in photon gases until the researchers successfully secured precisely this proof. They measured spatial correlations, i.e. how strongly the state of the light at different positions is related, in a nearly non-interacting 2D photon gas trapped in a mirror box just before the Bose-Einstein condensation phase transition. From this, they determined the critical exponent – a quantity describing how sensitively the spatial extent of these correlations increases as the temperature changes near the phase transition.
They trapped light particles inside an optical microresonator – a microscopic cavity formed by two closely spaced mirrors – filled with a dye solution. Through processes of absorption and emission as the light particles came into contact with the dye molecules, the photons effectively cooled down (“thermalised”) to a point where the quantum phase of condensation began. One of the resonator mirrors had been structured at the nanometre scale beforehand by means of laser writing to create a box-like potential, i.e. a trap for the photons. The angular distribution of the light emitted was then measured with a camera and analyzed via Fourier transform to determine the spatial correlations.
This was the first-ever experiment that demonstrated that photon gases constitute a distinct, overarching universality class of physical systems in nature, meaning that they follow characteristic laws near a phase transition. Much like water, which at the critical point suddenly turns cloudy due to opalescence (i.e. increasingly large density fluctuations scatter light), the photon gas in this case exhibits a rapidly increasing and diverging correlation length with a specific exponent. This research finding thus fills a key gap in the physics of phase transitions and has the potential to open up exciting new avenues for basic research into systems that lie well outside thermal equilibrium as well as for future applications in optics.
The team consists of researchers from the Institute of Applied Physics at the University of Bonn (Leon Kleebank, Frank Vewinger, Martin Weitz), the Kirchhoff Institute for Physics at Heidelberg University (Julian Schmitt) and the Physics Institute at the National Autonomous University of Mexico (Arturo Camacho-Guardian, Victor Romero-Rochín, Rosario Paredes). The project was led by Professor Julian Schmitt (Heidelberg).
This text was adapted from the original press release by the University of Bonn.
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Otto Haxel Dissertation Award for STRUCTURES YRC members Klaus Paschek and Nikolas Liebster
We congratulate YRC STRUCTURES member Klaus Paschek and YRC alumnus Nikolas Liebster on receiving this year's Otto Haxel Award for Physics. The annual dissertation prize has been awarded by the KIT Freundeskreis und Fördergesellschaft e.V. (KFG) of the Karlsruhe Institute of Technology (KIT) in cooperation with the German Physical Society (DPG) since 2017. It honours the three best doctoral dissertations at KIT and at the universities of Göttingen and Heidelberg — the three institutions where nuclear physicist Otto Haxel (1909–1998) conducted his research.
Dr. Liebster received the award for his dissertation on Pattern Formation and Supersolid Sound Modes in a Driven Superfluid, completed in the research group of Markus Oberthaler at the Kirchhoff Institute for Physics (KIP) of Heidelberg University. His research focuses on quantum systems far from equilibrium, where novel steady states can emerge that have different properties from the same system at equilibrium. In certain cases, theoretical frameworks from equilibrium physics can be applied to understand their behaviour. In his thesis, Nikolas Liebster studied the emergence of such a steady state far from equilibrium, specifically in a Bose-Einstein condensate with periodically modulated interactions. The modulation results in the emergence of self-organized lattice structures, effectively crystallizing the system. Dr. Liebster showed that this far-from-equilibrium state has the properties of a supersolid, a strange state of quantum matter that is simultaneously solid and superfluid. This work provides new insights into pattern formation and the nonlinear dynamics of quantum fluids.
Dr. Paschek received the award for his dissertation From Space to the Hadean Earth: Prebiotic Synthesis and the Origins of Life, completed in the laboratory astrophysics group led by Thomas Henning at the Max Planck Institute for Astronomy (MPIA). In his thesis, he investigated how the first building blocks of life may have arisen on the early Earth several billion years ago. Organic molecules and their precursors could have been brought to Earth by meteorites, whose impacts back then were far more frequent – or they could have formed on Earth itself in what are known as “Darwin’s warm little ponds”. These are shallow, warm bodies of water, in which compounds produced from volcanically released gases and atmospheric photochemistry could have accumulated and undergone further prebiotic reactions. In his thesis, Dr. Paschek showed that both scenarios can provide viable pathways toward the formation of RNA building blocks and other prebiotic molecules under plausible early-Earth conditions. In particular, his work shows that a previously problematic aspect of the terrestrial scenario – an early atmosphere thought to be too oxidizing for efficient prebiotic chemistry – could have been overcome by geological processes such as serpentinization, while also providing a quantitative explanation for how key prebiotic molecules could form in carbonaceous meteorite parent bodies before being delivered to Earth.
The award ceremony took place on July 13, 2026, at the KFG summer reception on the KIT South Campus in Karlsruhe. The Otto Haxel Award was established by Hans Joachim Langmann in memory of his doctoral advisor.
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From 5–9 October 2026, the 57th Heidelberg Physics Graduate Days will once again bring together doctoral researchers of the Department of Physics and Astronomy at Heidelberg University. The event, which takes place biannually and is supported by the STRUCTURES Cluster of Excellence, offers advanced students and researchers a biannual spring/autumn school featuring different topics from various fields of physics.
The Physics Graduate Days reflect the breadth of modern physics and its interdisciplinary perspectives – from artificial intelligence (AI) in particle physics to quantum communication systems, from emergent spacetime to biological self-organization, and from quantum gases to black holes. The courses offer insights beyond the standard curriculum and highlight connections with scientific computing, mathematics and numerical methods, biology, and technological applications.
This year's speakers are Sascha Diefenbacher, Raúl Carballo-Rubio, Ivelina Momcheva, Stefan Floerchinger, Dominik Mitzel, Francesca Giacoppo, Julian Schmitt, Alex Vañó Viñuales, Beatrice Ramm, Pascal Kobel, Shep Doeleman, and the d-fine Team.
A special highlight of the programme will be the Hans Jensen Invited Lecture by Shep Doeleman (Harvard) on Taking Pictures and Making Movies of Supermassive Black Holes. Moreover, as a special event, this year's Graduate Days will host the Wilhelm und Else Heraeus-Stiftung Symposium and Award Ceremony for outstanding PhD theses!
The courses are open to advanced students, in particular those working on their Master's and doctoral theses. Our aim is to offer courses that broaden the physics knowledge of our students as well as to teach specialized techniques. The courses are organized as parallel block lectures, with the morning lectures taking place from 9:30 to 12:30 and the afternoon lectures from 14:00 to 17:00, including coffee breaks. There is also a free lunch each day included in your registration. Note that each course runs every day for four days, either in a morning or afternoon slot.
The Scientific Advisory Team consists of Dr. Sanam Vardag, Tristan Bereau, Astrid Eichhorn, Annalisa Pillepich, Eduard Thommes, Rainer Stamen, Werner Rodejohann, Björn Malte Schäfer, Louis Jussios and Jonathan Steiner.
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Prof. Cornelis Dullemond (ZAH)We warmly congratulate our member Cornelis P. Dullemond (Centre for Astronomy Heidelberg, ZAH) on receiving the 2026 Astrophysical Software Award of the German Astronomical Society. The award recognizes his conception, development, and long-term stewardship of the radiative transfer software RADMC-3D.
The RADMC-3D software package has become one of the leading frameworks for modelling radiative transfer in gas and dust; and for generating synthetic observations for comparisons with astronomical data. It is widely used across a broad range of research areas in astrophysics, including protoplanetary disks, star formation, evolved stars, and active galactic nuclei.
In its citation, the Astronomical Society emphasized the flexibility and reliability of the RADMC-3D, which have established it as standard tool used by researchers worldwide. As a result, they conclude “RADMC-3D has played a key role in transforming theoretical models into testable predictions and has enabled significant advances in our understanding of the Universe.”
Cornelis Dullemond has been Professor of Theoretical Astrophysics at Heidelberg University's Centre for Astronomy (ZAH) since 2010, and has been a Principal Investigator of STRUCTURES since the start of the cluster in 2019. His research on the theoretical and numerical modelling of planet formation is closely aligned with the scientific scope of STRUCTURES' Comprehensive Project CP2 (From Dust to Planets).
The German Astronomical Society (AG) is the professional German national association for astronomy and astrophysics. The AG promotes activities in science and research, strengthens exchange between its members and supports the dissemination of science to the public and in education.
The award ceremonies will take place during the annual meeting of the German Astronomical Society in Garching from September 7-11, 2026.
Further information:
We are delighted to announce this year's YRC Schöntal Discussion Workshop on Dynamical Systems, which will take place from the 25th to the 28th of August at the quaint and charming Schöntal Abbey.
The aim of the workshop is to provide an opportunity for early-career scientists to gather and discuss topics that go beyond the standard mathematics and physics curriculum, and to approach different subjects from their respective fields of research. The goal is to encourage interdisciplinary scientific exchange between the various areas of the STRUCTURES Cluster.
This year, the overarching topic of Dynamical Systems will be the protagonist. As a key concept in many physical, mathematical, computational and biological applications, we expect it to foster collaboration across different fields and spark conversations that may lead to innovative and creative ideas and applications. The workshop will guide participants through the fundamentals of dynamical systems, including the distinction between continuous and discrete time systems, core concepts such as stability, chaos, and bifurcation theories, and modern applications ranging from training algorithms to recurrent neural networks (RNNs).
This year's invited experts are Dr. Zahra Monfared and Prof. Dr. Tim Laux.
To register, simply fill out the online registration form below. Participation is free of charge for STRUCTURES YRC members.
Registration form
Registration deadline: 24 July 2026.
Organizing team:
The workshop is organized by Alicia Castro, Alessandro Di Gregorio, Sander Hummerich, Luis Walter.
About the Young Researchers Convent (YRC):
This workshop is funded by STRUCTURES Young Researchers Convent (YRC), a subgroup of the STRUCTURES Cluster of Excellence dedicated to supporting early-career scientists. The YRC strives to help its members realize their own projects, and if you think your work fits within the concept of STRUCTURES, you are welcome to apply for YRC membership. If your supervisor is a STRUCTURES member, you are directly eligible.
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Public Lecture “Kanonen auf Spatzen: Eine große Reise durch die Mathematik für ein kleines Problem aus der Geometrie”
Sometimes simple questions require intricate mathematical solutions: We are excited to announce the public lecture by Prof. Dr. Günter M. Ziegler (Freie Universität Berlin), "Kanonen auf Spatzen: Eine große Reise durch die Mathematik für ein kleines Problem aus der Geometrie".
For his talk, Prof. Dr. Günter M. Ziegler will take his audience on a journey through mathematics to answer a seemingly simple geometry question, posed by R. Nandakumar on a blog post in September 2006: "Can every polygon be partitioned into a prescribed number of convex pieces, each with the same area and the same perimeter?"
The talk will take place on Friday July 10, 2026 at 5 pm in the new audiMAX lecture hall (INF 289), and is targeted especially to high school students and mathematics enthusiasts. The lecture will be in German.
All interested are welcome to attend, as the talk is free of charge, with no registration required. For further information, please visit the event’s website.
This event is organized by the Research Station Geometry + Dynamics, a research centre within the Institute for Mathematics (IMa) at Heidelberg University. The station brings together researchers working at the interface of geometry, topology, group theory, and dynamical systems. Alongside its research activities, it is committed to education and public engagement through outreach initiatives that make mathematics accessible to a wider audience.
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