A beautiful twist on condensed matter
Discussion meeting organised by Professor Christos Panagopoulos, Professor Neil Mathur and Professor Ramamoorthy Ramesh FRS.
There is currently great interest in the fundamental physics of topologically complex and elegant patterns that can arise or be created in magnetic, ferroelectric, and liquid crystal materials. This meeting will explore similarities and differences between the complex order in these classes of material. We will also focus on how the complex patterns may be exploited to encode and transmit information.
Programme
The programme, including speaker biographies and abstracts, will be available soon. Please note the programme may be subject to change.
Poster session
There will be a poster session from 5pm on Tuesday 28 April 2026. If you would like to present a poster, please submit your proposed title, abstract (up to 200 words), author list, and the name of the proposed presenter and institution no later than Friday 27 March 2026.
Attending the event
This event is intended for researchers in relevant fields.
- Free to attend
- Both virtual and in-person attendance is available. Advance registration is essential. Please register via Eventbrite for a ticket
- Lunch is available on both days of the meeting for an optional £25 per day. There are plenty of places to eat nearby if you would prefer purchase food offsite. Participants are welcome to bring their own lunch to the meeting
Enquiries: Scientific Programmes team.
Image credit: iStock.com / merrymoonmary
Organisers
Schedule
Chair
Professor Christos Panagopoulos
Nanyang Technological University, Singapore
Professor Christos Panagopoulos
Nanyang Technological University, Singapore
Christos Panagopoulos received his PhD from the University of Cambridge (Trinity College) and is Professor of Physics and Applied Physics at Nanyang Technological University, Singapore. His research programme is directed toward the discovery and characterisation of materials with complex quantum order, the advancement of experimental methodologies capable of probing correlations across diverse length and time scales, and the development of theoretical frameworks elucidating the role of wavefunction geometry and topology in governing material properties. By integrating these approaches, he establishes rigorous connections between the underlying quantum architecture of matter and emergent device functionalities, thereby contributing to both fundamental understanding and prospective technological innovation.
| 08:55-09:00 |
Welcome by the Royal Society and lead organiser
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| 09:00-09:30 |
Reversible fusion of particle-like chiral nematic and magnetic vortex knots
Vortex knots have been seen decaying in many physical systems. Here we describe topologically protected vortex knots, which remain stable and undergo fusion and fission while conserving a topological invariant analogous to that of baryon number. While the host medium, a chiral nematic liquid crystal, exhibits intrinsic chirality, cores of the vortex lines are structurally achiral regions where twist cannot be defined. We refer to them as "dischiralation" vortex lines, in analogy to dislocations and disclinations in ordered media where, respectively, positional and orientational order is disrupted. Fusion and fission of these vortex knots, which we reversibly switch by electric pulses, vividly reveal the physical embodiments of knot theory's concepts like connected sums of knots. Our findings provide insights into related phenomena in fields ranging from cosmology to particle physics and can enable applications in electro-optics and photonics, where such fusion and fission processes can be used for controlling light. 
Professor Ivan SmalyukhUniversity of Colorado Boulder, US
Professor Ivan SmalyukhUniversity of Colorado Boulder, US Ivan I Smalyukh is a tenured professor at the Department of Physics, University of Colorado at Boulder, which he joined in 2007 (promoted from Assistant to Associate Professor with tenure in 2014 and from Associate to Full Professor in 2017). He is also the Founding Director of the International Institute for Sustainability with Knotted Chiral Meta Matter, as well as the founding fellow of Renewable Sustainable Energy Institute, a joint institute of CU-Boulder and NREL. He is an elected fellow of APS, AAAS, Optica and SPIE. He received many awards, including the Bessel and Glenn Brown Awards, Gray Medal, NASA iTech award and Mid-Career Award of the International Liquid Crystal Society, the PECASE Award from the Office of Science and Technology of the White House and the GSoft Award from the American Physical Society. |
| 09:30-09:45 |
Discussion
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| 09:45-10:15 |
Topological defects in nematic colloidal crystals
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| 10:15-10:30 |
Discussion
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| 10:30-11:00 |
Break
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| 11:00-11:30 |
Lorentz electron ptychography on centrosymmetric skyrmions
Electrons play a pivotal role in stabilizing matter, but they are also tools that can reveal the underlying physics of complex systems from high energy physics to condensed matter. Electrons can be used as imaging probes, where properties of matter such as ferroelectricity, magnetism or topology can be observed atom-by-atom. In this talk, I will discuss a new type of electron probe which can image the chiral order of centrosymmetric magnetic skyrmions called Lorentz electron ptychography, an iterative phase retrieval imaging technique for magnetic materials. In particular, my research focuses on amorphous layered thin films of FeGdPt, which have been shown to form centrosymmetric skyrmions with a predicted internal Bloch wall and Néel caps. Using simulation and experimental results from Lorentz electron ptychography and four-dimensional scanning transmission electron microscopy, I show that this structure does indeed have a hybrid Bloch and Néel skyrmion structure, as predicted from micromagnetic simulations. Finally, I will also show how electron ptychography can improve resolution beyond the numerical aperture of the electromagnetic lenses to the sub-angstrom limit in a conventional electron microscope. Using this technique, I essentially develop a ‘computation lens’ approach to imaging, opening opportunities to explore new physics in emergent materials beyond physical lenses in a cost-effective manner, and thus expanding access to high-resolution imaging approaches to a broader range of institutions. 
Professor Kayla NguyenUniversity of Oregon, US
Professor Kayla NguyenUniversity of Oregon, US Dr Kayla Nguyen has made a tremendous impact in the field of transmission electron microscopy. She earned her undergraduate degree in Physics from the University of California Santa Barbara, and PhD from Cornell University. At Cornell, she provided a critical role in the development of a novel pixel array detector for electron microscopes with unprecedented dynamic range, sensitivity, and speed. This new detector has been licensed and sold around the world by Thermo Fisher Scientific. During her postdoctoral fellowship at the University of Illinois Urbana-Champaign, she won the L’Oreal For Women in Science Postdoctoral Fellowship and was named a promising Asian researcher by The Japan Times. In 2023, she became an Assistant Professor at the University of Oregon where she received a coveted Arnold and Mabel Beckman Young Investigator, the Army Research Office Early Career Program Award, the National Scientific Foundation MRI for a new TEM, and industry sponsored research from Intel to continue her cutting edge work. Her passion for science extends beyond the laboratory setting, towards developing accessible pathways for young scientists in STEM. |
| 11:30-11:45 |
Discussion
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| 11:45-12:15 |
Phase transformations in chiral magnets: the role of anisotropy
The magnetic phase diagrams of cubic chiral magnets follow a similar pattern consisting of the helical spiral, conical spiral, and the skyrmion lattice phase, which appears in a narrow pocket of the phase diagram, the so-called A-phase, just below the magnetic ordering temperature. A remarkable exception to this universality is the Mott insulator Cu2OSeO3, where robust skyrmionic states can be produced over large areas of the magnetic phase diagram from the lowest temperatures up to the A-phase. Furthermore, when the field is applied along the [001] easy crystallographic axis and its value is just below the critical field at which the conical spiral state disappears, the spiral wave vector rotates away from the magnetic field direction leading to a multidomain tilted spiral state. This phase occurs where it is least expected, at low temperatures, where thermal spin fluctuations are suppressed, and at magnetic fields strong enough to align all spirals along their direction. Nascent and disappearing (tilted) spirals catalyze topological charge changing processes, leading to the formation of skyrmionic states at low temperatures, which are thermodynamically stable or metastable, depending on the orientation and strength of the magnetic field. The metastable low temperature skyrmions are extremely robust and surprisingly resilient to high magnetic fields: the memory of skyrmion states persists in the field polarized state, even when the skyrmion lattice signal has disappeared. A in depth comparison between experiment and theory leads to the conclusion that the driving forces behind the observed unconventional behaviour are temperature dependent competing anisotropies, generic to chiral magnets. These competing anisotropies and may stabilize novel skyrmionics states in a wide range of magnetic fields and temperatures, beyond the A-phase, and thus provide an additional lever for tailoring the properties of chiral magnets. 
Professor Catherine PappasDelft University of Technology, The Netherlands
Professor Catherine PappasDelft University of Technology, The Netherlands Catherine (Katia) Pappas joined 2009 Delft University of Technology to lead the section Neutron and Positron Methods in Materials (NPM2), within the Faculty of Applied Sciences. Her field of expertise is in neutron scattering science and techniques, with focus on high-resolution (neutron spin echo) spectroscopy and polarized neutrons. Besides neutron instrumentation, her scientific interests are in the field of magnetism and chiral magnetism, and the field of skyrmions. Before Delft Katia spent several years at the Hahn-Meitner Institute – nowadays Helmholtz Zentrum Berlin – where she was involved in numerous large scale neutron instrumentation projects. She was deputy director of the Berlin Neutron Scattering Center and head of the "Neutron Instruments and Methods" department. In Delft, she was again the initiator of several big instrumentation projects, such as the neutron powder diffractometer PEARL or the multipurpose instrument LARMOR, a Dutch-UK collaboration, which is being built at the UK neutron source ISIS and is supported by the Dutch Science Foundation (NWO). |
| 12:15-12:30 |
Discussion
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Chair
Professor Karin Everschor-Sitte
University of Duisburg-Essen, Germany
Professor Karin Everschor-Sitte
University of Duisburg-Essen, Germany
Karin Everschor-Sitte is a professor of Theoretical Physics at the University of Duisburg-Essen in Germany. Her main scientific research fields are the complex fundamental physics of topological magnetic textures and spintronics-based unconventional computing. After completing her PhD at the University of Cologne in 2012, Karin Everschor-Sitte worked as a postdoc at the Technical University Munich and then received a DAAD postdoctoral fellowship to conduct research at the University of Texas at Austin. Followed by a period as a postdoc, she led an Emmy Noether group at the Johannes Gutenberg University Mainz, from 2016 to 2021. In 2018, she received the Hertha-Sponer-Prize, and in 2024, she was honoured as the Wohlfarth Lecturer.
| 13:30-14:00 |
X-ray tomography
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| 14:00-14:15 |
Discussion
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| 14:15-14:45 |
Emergent light-matter interactions in ferroelectrics
The resonance frequency of the lattice polarization of most ferroelectric materials is in the terahertz (THz) range. Therefore, ferroelectric polarization can resonantly interact with a THz electromagnetic wave. In this talk, the speaker will discuss how such resonant interaction can be utilized to (1) modulate the amplitude, phase, and even the chirality of a THz wave transmitting through a freestanding ferroelectric membrane, using BaTiO3, strained SrTiO3, LiNbO3, and ScAlN as examples; (2) create new hybridized states from the strong coupling between the quanta of coherent polarization waves (aka coherent ferrons) and standing bulk acoustic waves (ie, cavity acoustic phonons), using a freestanding van der Waals (vdW) ferroelectric CuInP2S6 membrane as an example; (3) achieve the resonant coupling between ferroelectric domain walls and acoustic phonons, using a strained BaTiO3 membrane as an example; and (4) activate new, acoustically amplified, topological modes of the periodically aligned flux closures in strained cation-doped BaTiO3 thin films. These predictions are based on dynamical phase-field simulations and complementary analytical calculations. An outlook for the development of thermodynamic theory and dynamical phase-field model for predicting the optical, electro-optic, and elasto-optic properties of oxide, nitride, and vdW ferroelectric materials will also be presented. 
Professor Jiamian HuUniversity of Wisconsin-Madison, US
Professor Jiamian HuUniversity of Wisconsin-Madison, US Dr Jiamian Hu is an Associate Professor in the Department of Materials Science and Engineering at the University of Wisconsin (UW)-Madison. Dr Hu received the Vilas Associate Award for research from UW-Madison, the Innovation Award from the Wisconsin Alumni Research Foundation, the Robert L Coble Award for Young Scholars from the American Ceramic Society, and the National Science Foundation CAREER award. Dr Hu has published over 100 peer-reviewed articles and is the lead inventor of five granted US Patents. His current research activities include mesoscale modeling of ferroic (magnetic, ferroelectric, and multiferroic) materials, polar semiconductors, and the resulting quantum and microelectronic devices, microstructure formation and evolution under nonequilibrium conditions, and microstructure informatics. Dr Hu served as an Associate Editor for the Journal of Materials Research and an Editorial Board Member of Journal of Physics D: Applied Physics. |
| 14:45-15:00 |
Discussion
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| 15:00-15:30 |
Break
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| 15:30-16:00 |
Dynamics of chiral textures in thin magnetic film stacks with Dzyaloshinskii Moriya interaction and their manipulation by electric fields
The dynamics of homochiral domain walls in ultra thin ferromagnetic (FM) layers deposited on a heavy metal (HM) in asymmetric stacks is strongly modified by the presence of interfacial Dzyaloshinskii-Moriya interaction (DMI). In particular, the Walker field beyond which the field-driven mobility strongly decreases can be pushed to larger fields, allowing reaching very large velocities, proportional to the strength of the DMI. Similarly, DW velocities driven by spin-orbit torque (SOT) are also enhanced in systems with large DMI. In HM/Co/oxide trilayers the DMI strength and the magnetic anisotropy energy results from contributions of both the bottom and the top Co interfaces. When the latter are manipulated by magneto-ionic effects tuning the oxidation degree of the Co top interface, the resulting DW dynamics is strongly affected. This will be demonstrated for the case of a Pt/Co/AlOx trilayer. The propagation direction of SOT-driven chiral textures depends also on the sign of the DMI. We will show that this can be reversed by finely tuning the degree of oxidation of the FM layer with a gate voltage, which in Ta/CoFeB/TaOx trilayers can lead to a reversal of skyrmion direction of motion. Hard x-ray photoelectron spectroscopy measurements on Pt/Co/oxide/HfO2 capacitor-like devices allowed us to prove that in our integrated devices, the gate voltage modifies the PMA and the DMI through the modification of the oxidation degree of the Co layer, driven by oxygen-ion migration through the HfO2 dielectric layer. This local degree of freedom at the nanometer scale controlled with gate voltages compatible with applications could lay the foundations for efficient architectures involving domain walls or magnetic skyrmions as information carriers. 
Dr Stefania PizziniInstitut Néel, CNRS, France
Dr Stefania PizziniInstitut Néel, CNRS, France Stefania Pizzini obtained her Physics Degree from Università degli Studi di Milano (Italy) in 1986. She then moved to the UK where she worked on the structural characterisation of condensed interfaces using x-ray absorption spectroscopy at the Daresbury synchrotron radiation sources, and obtained her PhD from the University of Strathclyde in Glasgow in 1990. In 1991 she moved to the French synchrotron radiation source laboratory in Paris with a Marie Curie PostDoc fellowship, where she worked on the characterization of magnetic properties of ultrathin magnetic films using x-ray circular magnetic dichroism (XMCD). In 1994 she obtained a research position at Laboratoire Louis Néel in Grenoble, laboratory associated to the Centre National de la Recherche Scientifique. In the 1990s she was involved in the implementation of XMCD at the energy-dispersive x-ray absorption beamline of ESRF and the development of time-resolved XMCD and XMCD-PEEM techniques. In more recent years she has specialised in the study of domain wall (DW) dynamics in chiral thin film heterostructures and the manipulation of magnetic properties with magneto-ionic effects. |
| 16:00-16:15 |
Discussion
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| 16:15-17:00 |
Poster flash talks
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Chair
Dr Olga Kazakova
National Physical Laboratory, UK
Dr Olga Kazakova
National Physical Laboratory, UK
Olga Kazakova is a Fellow of the National Physical Laboratory (NPL), London, UK, and currently serves as Chair of NPL’s Senior Science College. Her research lies at the intersection of Materials Science and Quantum Technology, with a particular focus on materials for quantum applications. Previously, Olga has led pioneering work in advanced imaging techniques for functional nanoscale studies, the development of novel sensors for environmental monitoring, life sciences, and food safety, as well as metrological innovations. She is the author of approximately 200 peer-reviewed publications and has delivered over 180 presentations at scientific conferences, including more than 80 invited talks and seminars. Her contributions have been recognised with numerous national and international awards, such as the Intel European Research and Innovation Award, NPL Rayleigh Award, and Serco Global Pulse Award. Olga is a Fellow of the Institute of Physics and holds a Professorship at the University of Manchester.
| 09:00-09:30 |
Diamond magnetometry
Professor Satoshi AyaSouth China University of Technology, China
Professor Satoshi AyaSouth China University of Technology, China Satoshi Aya is an experimental physicist specializing in soft condensed matter. He obtained his PhD from the Tokyo Institute of Technology and is currently a tenured professor at the School of Emergent Soft Matter, South China University of Technology in China. Before joining South China University of Technology, he worked as an R&D engineer at Hitachi High-Tech Corporation and a postdoctoral researcher at RIKEN. His recent research interests include the development of ferroelectric fluids, the design of complex domain structures using liquid-crystalline orders, mean-field modeling of polar topology in liquid matter, and the application of non-classical polar structures in liquid-matter nonlinear optics and ferroelectronics. |
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| 09:30-09:45 |
Discussion
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| 09:45-10:15 |
Merons and bimerons in an antiferromagnet
Professor Paolo Radaelli, University of Oxford, UK
Professor Paolo Radaelli, University of Oxford, UKPaolo G Radaelli is the Dr Lee’s Professor of Experimental Philosophy at the Department of Physics, Oxford University. Following a Laurea degree at the Università degli Studia di Milano and a PhD at Illinois Institute of Technology, Professor Radaelli has held posts at the Argonne National Laboratory, CNRS Grenoble, the Institute Laue–Langevin and the ISIS Facility at the Rutherford Appleton Laboratory. His main interest is the study of transition metal oxides displaying novel physical phenomena, such as high-temperature superconductivity, “colossal” magneto-resistance or multiferroics behaviour, with the potential of device applications. |
| 10:15-10:30 |
Discussion
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| 10:30-11:00 |
Break
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| 11:00-11:30 |
Harnessing skyrmion helicity for novel functionalities
Chirality is a fundamental concept in physics, appearing in everything from particle properties to emergent quasiparticles such as skyrmions, topologically protected spin textures with twisted configurations defined by helicity. While helicity is typically fixed in chiral magnets, frustrated magnets offer a new platform where helicity becomes a free parameter, enabling richer excitation spectra and complex magnetization dynamics. In this talk, I present magnetic nano-skyrmions as candidates for quantum logic elements, focusing on their potential in quantum computing. I then turn to collective spin-wave excitations, where hybridization between internal skyrmion modes and magnons gives rise to dynamical magnon superlattices, interference patterns of localized spin waves. In skyrmion lattices, these localized modes form complex magnonic bands with nontrivial Chern numbers, further enriched by long-range interactions. These findings reveal a rich interplay between frustration, topology, and dynamics, and open new directions for skyrmion-based magnonic devices beyond the conventional chiral paradigm. 
Dr Christina PsaroudakiEcole Normale Supérieure Paris, France
Dr Christina PsaroudakiEcole Normale Supérieure Paris, France Christina Psaroudaki is a theoretical condensed-matter physicist and the Mitsubishi Heavy Industries Chair of Quantum Information at the Laboratoire de Physique de l’École Normale Supérieure (LPENS), Paris. Her research explores the quantum properties of topological magnetic textures, including skyrmions and spin-based platforms for quantum information. Before joining ENS, she held research postdoctoral positions at the University of Cologne, Caltech, and the University of Basel. She received her PhD from the University of Crete, Greece, where she worked on topics of quantum magnetism and strongly correlated systems. |
| 11:30-11:45 |
Discussion
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| 11:45-12:15 |
Reservoir computing using chiral magnets
Neuromorphic computing is a non-von Neumann architecture that mimics and exploits the human brain functionality. Viable neuromorphic computers require significant, overarching development across computer algorism, integrated circuit and device levels. Reservoir computing (RC) [1] is one of the recurrent neural network architectures that gain computational performance by using high dimensional mapping, in a similar way as the kernel method/trick for e.g. nonlinear pattern classification. A small number of weight optimisation defines a key strength of RC, making it suit to low-energy and time-series computational tasks. Inspired by the current trend of physical RC [2]. we use the physical response for the high-dimensional mapping element in RC and developed a physical RC architecture with chiral magnets having rich thermodynamical magnetic phases i.e. helical, conical and magnetic skyrmions. Their spectral responses allow convenient high-dimensional mapping, enabling simple computational tasks, ie signal transformation and future prediction, for this approach [3-4]. We find that different magnetic phases possess dissimilar computational performance, owing to their physical properties and I will show basic correlation between the performance and other metrics to characterise the physical system. From our study, we argue that exploiting multiple thermodynamical phases in a single material is beneficial in adopting their computational performance to a different set of computational tasks, something used to be difficult to achieve in a physical RC system but easily implemented by hyperparameter optimisation in software machine learning. [1] H Jaeger and H Haas, Science 304, 78 (2004) 
Professor Hidekazu KurebayashiUniversity College London, UK
Professor Hidekazu KurebayashiUniversity College London, UK Hide Kurebayashi is Professor of Condensed Matter Physics and Nanoelectronics at two institutes, UCL and Tohoku University. Before joining UCL, he worked at the University of Cambridge as a JST-PRESTO research fellow in the Cavendish laboratory, where he also completed his PhD in 2010. He leads two experimental research groups in the UK and Japan, working on spintronics and spin dynamics. His recent research interest includes spin-orbit transport in inversion-broken and/or low-dimensional crystals such as van der Waals materials, neuromorphic computing and coherent photon-magnon coupling in nano-systems. For his research, he received the JSPS Prize, Leverhulme Research Fellowship, The Young Scientists’ Award within The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology by Japanese government, UCL Future Leader Award, JST-PRESTO Research Fellowship, Darwin College Research Fellowship, Runner-up of the Abdus Salam Prize, ORS and the Nakajima Foundation scholarship. |
| 12:15-12:30 |
Discussion
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Chair
Professor Jorge Íñiguez-González
Luxembourg Institute of Science and Technology, Luxembourg
Professor Jorge Íñiguez-González
Luxembourg Institute of Science and Technology, Luxembourg
Jorge Íñiguez-González is a group leader at the Luxembourg Institute of Science and Technology and affiliate full professor of Physics at the University of Luxembourg. His work focuses on the application of quantum simulation methods to problems at the frontier of materials science, including extensive studies of functional nanomaterials as well as methodological developments for predictive large-scale simulations. Recent highlights include the discovery of topological electric quasiparticles or “electric skyrmion bubbles”. He is a Fellow of the American Physical Society “For ground-breaking contributions to the computational theory of ferroelectric and multiferroic materials.
| 13:30-14:00 |
Toroidal topologies in ferroelectric polymers and their electrical controls
Strong dielectric anisotropy in ferroelectric materials normally prefers rigid dipole alignment with crystallographic axes and lead to simple polar structures. Lamellar crystals of ferroelectric polymers based on poly(vinylidene fluoride) comprise molecular chains preferentially aligned along a common lattice direction, which preserves a rotational degree of freedom about the chain backbone. I will explain how dipoles in ferroelectric polymers can therein be frustrated into toroidal topologies, either mechanically via biaxial tensile strain, or chemically through conformational disorder. When an out-of-plane electric field or mechanical pressure is applied with a small magnitude, the toroidal topology undergoes continuous rotation without being destroyed. In contrast, an in-plane electric field annihilates the toroidal topology, which could be reversible created upon field removal. Given that polymers absorb infrared radiation in a selective manner, these field-modified topological states can be read out using plane-polarised radiation. The ability to rotate, erase, and create these toroidal textures offers prospects for reconfigurable electronic and photonic devices. 
Dr Mengfan GuoUniversity of Cambridge, UK
Dr Mengfan GuoUniversity of Cambridge, UK Dr Mengfan Guo is a Goldsmiths' Early Career Research Fellow at University of Cambridge, and a former Royal Society Newton International Fellow. He received BS and PhD degrees from Tsinghua University in 2016 and 2021, respectively. His research focuses on polar materials, particularly the static and dynamic arrangements of electrical dipoles that give rise to emergent properties. A research highlight is the discovery of toroidal topologies in ferroelectric polymers. His work has been published in Science, Nature Energy, Nature Nanotechnology etc. He has been recognized as an Outstanding Graduate in Beijing, a Tsinghua Top Academic Talent, and a recipient of the Excellent Doctor Degree Dissertation Award in both Beijing and Tsinghua University. |
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| 14:00-14:15 |
Discussion
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| 14:15-14:45 |
Emergence of transverse dielectric response in ferroelectric dielectric heterostructures
We report the emergence of a transverse dielectric response in PbTiO3/SrTiO3 superlattices hosting polar vortex structures. Using second-principles simulations, we find that an electric field applied along one direction induces significant local polarization responses along orthogonal directions, with magnitudes approaching half that of the diagonal susceptibility components. These off-diagonal responses are strongly dependent on the topology of the vortex structure and can be deterministically tuned or even reversed via homogeneous electric fields or epitaxial strain. Notably, the transverse susceptibilities become comparable to the diagonal components during a field- or strain-induced transition to a polarization wave state. This discovery opens avenues for engineering reconfigurable nanoscale dielectric responses in topologically textured ferroelectric systems. 
Professor Javier JunqueraUniversidad de Cantabria, Spain
Professor Javier JunqueraUniversidad de Cantabria, Spain Professor Javier Junquera is a theoretical condensed matter physicist and core developer of the SIESTA code for large-scale first-principles simulations. His research combines methodological innovation with the application of ab-initio and “second-principles” approaches to ferroelectric and topological materials. He has made key contributions to understanding size effects, depolarizing fields, and band alignment in oxide nanostructures, and to predicting emergent polar textures (such as polar skyrmions and vortex arrays) in ferroelectric superlattices in collaboration with the Ramesh group at UC Berkeley. These studies unveiled novel topological phases in polar materials, featuring negative capacitance, chirality, and phase coexistence. His ongoing work focuses on multiscale “second-principles” simulations coupling electronic and ionic degrees of freedom to access mesoscale phenomena with first-principles accuracy. Fellow of the American Physical Society in the division of Material Science. |
| 14:45-15:00 |
Discussion
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| 15:00-15:30 |
Break
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| 15:30-16:00 |
Moiré polar topologies in twisted oxide membranes
The recent realization of membranes of perovskite oxides, has enabled their assembly into twisted homo bilayers. In twisted BaTiO3 membranes, these inhomogeneous strain patterns underlay the formation of an array of ferroelectric vortices driven by the flexoelectric coupling of polarization to strain gradients [1]. Surprisingly, the shear interaction developing at the interface, driven by the mostly incoherent atomic registry between the two twisted layers, propagate into the layers, relaxing over distances which can be as long as tens of nanometers. The decaying nonhomogeneous strain triggers profound changes in the polarization landscape which evolves from a pure rotational polarization pattern with alternating ferroelectric vortices and antivortices to a superposition of a vortex lattice and a homogeneous polarization component. Yet, flexoelectricity is a universal phenomenon which may render polar landscapes in non-ferroelectric materials. Here we report a flexoelectrically induced polar topology in twisted membranes of SrTiO3, a paraelectric centrosymmetric material. The polar landscape triggered by twisting is also supported by machine learned force fields based on first-principles calculations. We further show that the strain and polarization patterns in top and bottom layers are correlated in a way which breaks inversion and mirror symmetries thus unlocking a chirality degree of freedom. [1] G. Sanchez-Santolino et al. Nature 626, 529 (2024)
Professor Jacobo Santamaría, Universidad Complutense de Madrid, Spain
Professor Jacobo Santamaría, Universidad Complutense de Madrid, Spain
Jacobo Santamaria is a Full Professor of Physics at the Physics Faculty of the Universidad Complutense de Madrid (Spain). He leads the “Complutense” Research Group of Complex Materials devoted to the study of magnetism and superconductivity of correlated oxide nanostructures. His interest focuses on interface phenomena in complex oxide superlattices. He has coauthored more than 200 publications in peer reviewed Journals. He is a Fellow of the American Physical Society and a Program Manager of Materials Sciences for the Spanish Ministry of Science and Innovation.
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| 16:00-16:15 |
Discussion
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| 16:15-17:00 |
Panel discussion/overview (future directions)
Professor Christos PanagopoulosNanyang Technological University, Singapore
Professor Christos PanagopoulosNanyang Technological University, Singapore Christos Panagopoulos received his PhD from the University of Cambridge (Trinity College) and is Professor of Physics and Applied Physics at Nanyang Technological University, Singapore. His research programme is directed toward the discovery and characterisation of materials with complex quantum order, the advancement of experimental methodologies capable of probing correlations across diverse length and time scales, and the development of theoretical frameworks elucidating the role of wavefunction geometry and topology in governing material properties. By integrating these approaches, he establishes rigorous connections between the underlying quantum architecture of matter and emergent device functionalities, thereby contributing to both fundamental understanding and prospective technological innovation. |