Topological insulators are among the strangest states of matter ever conceived. Their interiors are electrically inert, yet their surfaces or edges host channels of current that are protected by the mathematics of the material’s quantum wavefunction. In two-dimensional topological insulators, these channels come in counter-propagating pairs in which the direction of motion is locked to the spin of the electron, a configuration known as a helical edge mode. Because backscattering would require flipping an electron’s spin, these currents are predicted to flow with near-perfect efficiency, resisting the defects and impurities that degrade ordinary conductors. Harnessing them could enable dissipationless electronics and even serve as a platform for exotic quasiparticles useful in topological quantum computing.

Zirconium pentatelluride, or ZrTe5, promised to be the cleanest realization of this physics. It is a layered van der Waals crystal in the transition-metal pentatelluride family, and early experiments suggested it might sit on the boundary between a weak topological insulator and a three-dimensional Dirac semimetal, flipping between the two phases with subtle changes in temperature or lattice parameters. Transport measurements had hinted at two-dimensional edge transport, and the material displays spectacular bulk responses, including an enormous magnetoresistance and one of the strongest chiral magnetic effects ever recorded. Yet the decisive fingerprint, the helical edge state itself, remained stubbornly invisible. Bulk conduction swamped the edge signal, and the electrical contacts used in conventional transport experiments averaged over regions far larger than the nanometer-scale channels theorists predicted.

The new study, led by a team using cryogenic scanning probe techniques, took a fundamentally different approach. Rather than measuring current flow between two contacts, the researchers brought a nanoscale sensor to within a few tens of nanometers of the crystal surface and mapped the local magnetic and electronic landscape of individual ZrTe5 flakes. This imaging capability allowed them to distinguish conduction along the perimeter of the sample from conduction through its interior, a distinction that no contact-based measurement could make. When they scanned freshly exfoliated flakes at cryogenic temperatures, they found something unexpected: the edges were, at first, essentially featureless. The edge modes were dark.

That null result turned out to be the key. The team reasoned that in ZrTe5, the edge and bulk bands may be nearly degenerate, meaning the topological edge channels are so weakly bound to the boundary that they hybridize with the bulk and lose their identity, a situation that would render them invisible to transport and to most local probes. Applying a magnetic field perpendicular to the layers changes that balance. The field quantizes the bulk bands into Landau levels, pushing bulk carriers out of the relevant energy window and suppressing their hybridization with the edge. In this regime, the edge modes decouple and “brighten,” becoming visible as robust one-dimensional channels. The researchers observed precisely this: as the field increased past a threshold, a conducting channel emerged along the sample boundary that grew steadily more dominant while bulk conduction collapsed.

Crucially, the brightened channels carried the signatures of helical edge states rather than the ordinary quantum Hall channels that appear in the bulk under high magnetic fields. By combining local imaging with spin-sensitive measurements, the team showed that the edge conductance approached values consistent with a single pair of helical modes, and that the channels persisted around corners and across defects in ways that reflect topological protection. In the quantum Hall regime, adjacent edges would carry currents of opposite chirality dictated entirely by the magnetic field; the observed edge behavior instead matched the expectations for spin-momentum-locked conduction, in which the two spin sectors counter-propagate along the same boundary.

The implications reach well beyond one material. For years, the community has debated whether ZrTe5’s unusual transport arises from topological surface states, from strongly correlated effects, or from more mundane mechanisms such as inhomogeneous current paths. The magnetic brightening mechanism offers a unifying picture: the edge states exist even at zero field but are hybridized with the bulk, and the various anomalies reported across different experiments may reflect different degrees of that hybridization depending on sample thickness, strain, and temperature. It also suggests a practical strategy for accessing edge physics in other borderline topological materials where bulk and edge bands compete: use symmetry-breaking perturbations, magnetic fields chief among them, to spectrally separate the two.

The imaging methodology itself is a significant advance. Nanoscale imaging of one-dimensional quantum channels has long been limited by sensitivity and spatial resolution, and most techniques require electrical contacts that can perturb the very states under study. The contactless scanning approach demonstrated here can resolve features on the scale of the magnetic length, the natural length scale of Landau quantization, and can track how local conductance evolves continuously as field, temperature, and gating conditions change. The authors showed that the brightened edge signal correlates with the region of the sample where the bulk is fully gapped by Landau quantization, providing a direct spatial test of the brightening mechanism.

There is also a technological undercurrent to the result. Spin-polarized one-dimensional channels are a resource for spintronics, where information is carried by spin rather than charge, and for Majorana-based quantum information schemes, which typically begin by coupling helical edge states to superconductors. A material in which those channels can be switched on and off with a magnetic field offers a control knob that conventional topological insulators lack. ZrTe5 is additionally attractive because of its clean, layered crystals, which can be thinned, stacked, and integrated with other two-dimensional materials using established van der Waals assembly techniques, raising the prospect of designer heterostructures in which brightened helical edges serve as wiring for quantum devices.

The researchers caution that several questions remain open. The precise mechanism of hybridization between edge and bulk bands in zero field, the role of interactions in stabilizing the observed conductance values, and whether the brightened modes can survive at higher temperatures all warrant further study. Extending the imaging approach to spin-resolved detection at even finer resolution, and to superconducting proximity structures, are natural next steps. Still, the demonstration that an invisible quantum channel can be made to shine, and imaged directly as it does so, transforms a long-standing frustration in topological matter research into an opportunity. What was once hidden in ZrTe5 is now not only visible but controllable, and that visibility may prove to be the key to turning decades of topological theory into working devices.

At the core of Felser’s research lies the revolutionary domain of topological quantum chemistry, a field she has greatly influenced and helped to define. This discipline merges insights from quantum mechanics, materials science, and topology, providing a novel conceptual framework to understand and predict the electronic properties of materials. By leveraging the mathematical principles of topology — which studies properties preserved through continuous deformations — Felser and her colleagues are uncovering new classes of materials whose electronic behaviors cannot be explained by traditional band theory. This paradigm shift opens avenues toward designing materials that exhibit exotic phenomena such as robust edge states, quantum anomalous Hall effects, and spin-momentum locking.

Felser’s investigations into topological quantum materials extend beyond theoretical novelty. These materials hold immense promise for green energy applications due to their potential for ultra-efficient energy transport and conversion. For instance, topological insulators and semimetals can facilitate electronic conduction with minimal dissipation, a property that could drastically reduce energy loss in power grid components or thermoelectric devices. Her insights into magnetic compounds further complement these goals, as magnetism plays a crucial role in next-generation spintronics devices, which aim to exploit the electron’s spin degree of freedom to revolutionize memory storage and processing technologies.

The profound implications of Felser’s work are manifold. By bridging abstract theoretical frameworks with pragmatic material discovery, she is contributing to the development of sustainable technologies that align with global efforts to combat climate change. The materials studied in her lab may enable the creation of highly efficient solar cells, novel batteries, or electronic devices with drastically reduced carbon footprints. Moreover, topological phases offer a new platform for quantum computing paradigms, which require materials that can host stable quantum states resilient to environmental disturbances—a property found inherently in many topological materials.

Claudia Felser’s scientific journey is emblematic of the power of interdisciplinary research. Her expertise spans condensed matter physics, solid-state chemistry, and materials science, allowing her to approach complex problems with a comprehensive lens. This integrative approach has ushered in breakthroughs in not only understanding the underlying physics but also synthesizing and characterizing new compounds in the laboratory. Leveraging state-of-the-art experimental techniques such as angle-resolved photoemission spectroscopy (ARPES) and advanced magnetic resonance methods, Felser’s team probes the microscopic electronic structures and magnetic textures of novel materials.

In addition to her scientific excellence, Felser is a passionate advocate for social responsibility within the scientific community. She serves as Vice President of the Max Planck Society, one of the world’s leading research organizations, where she promotes inclusive and equitable scientific environments. Understanding the importance of cultivating the next generation of scientists, particularly women and underrepresented groups, she founded the NAT School Lab initiative. This program is dedicated to engendering scientific curiosity and engagement among young students, emphasizing hands-on learning and mentorship to empower future innovators.

The impact of Felser’s work resonates beyond academic circles. Her commitment to translating complex scientific concepts into tangible societal benefits underscores her vision of science as a powerful catalyst for progress. In her own words, “Science has always been a driving force for progress. It can help protect our societies, strengthen democracy, and ensure a livable future for generations.” This statement encapsulates the ethos guiding her research and leadership: a steadfast belief that science must serve society not only through technological advances but also by fostering resilience and equity.

Her accolades highlight the growing recognition of women leaders in scientific disciplines historically dominated by men. The L’Oréal-UNESCO For Women in Science International Awards, by spotlighting accomplished female scientists like Felser, are instrumental in challenging stereotypes and inspiring broader participation. Her recognition in this program signals a broader cultural shift towards valuing diversity as a driver of innovation and excellence in science.

The technical depth and visionary scope of Felser’s work make her a central figure in the quest to harness the peculiarities of quantum mechanics for practical ends. The concept of topology in materials provides a robust framework for creating devices whose performance surpasses that of traditional semiconductors and magnetic materials. As research in this field accelerates globally, Felser’s leadership ensures that Europe remains at the forefront of cutting-edge material science research, driving international collaborations and fostering interdisciplinary exchange.

Looking forward, the field of topological quantum chemistry promises to expand dramatically, fueled by theoretical insights, computational advances, and experimental breakthroughs alike. Felser’s ongoing projects focus on identifying new candidate materials, elucidating their quantum phase transitions, and exploring their possible applications in quantum information science. Her lab’s synthesis of previously unknown compounds is opening unexplored territory where physicochemical properties can be finely tuned, paving the way for disruptive technologies that will transform data storage, energy efficiency, and beyond.

In conclusion, Claudia Felser’s receipt of the 2025 L’Oréal-UNESCO For Women in Science International Award marks a milestone that celebrates both her scientific ingenuity and her commitment to social change. Her groundbreaking work on topological quantum materials not only advances fundamental understanding but also fuels innovation crucial for a sustainable and technologically advanced future. Her efforts exemplify the transformative power of interdisciplinary science and stand as a beacon for aspiring scientists worldwide.

Subject of Research: Topological Quantum Materials, Novel Magnetic Compounds, Topological Quantum Chemistry, Sustainable Energy Materials, Spintronics

Article Title: Claudia Felser: Pioneering Topological Quantum Chemistry for a Sustainable Future

Image Credits: © Fondation L’Oréal

Keywords

Physical sciences, Chemistry, Physics