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Key research directions and publication highlights.
Cavity quantum Hall systems
Cavity quantum Hall systems
We develop fundamental theory to explain recent quantum Hall experiments in the ultrastrong light–matter coupling regime, addressing cavity-modified transport, radiative properties, Landau polariton scattering, and strong correlations. Our goal is to bridge quantum Hall physics and cavity QED.
Weakened topological protection of the quantum Hall effect in a cavity, V. Rokaj, J. Wang, J. Sous, M. Penz, M. Ruggenthaler, A. Rubio, Physical Review Letters 131 (19), 196602 (2023).
Testing the renormalization of the von Klitzing constant by cavity vacuum fields, J. Enkner, L. Graziotto, F. Appugliese, V. Rokaj, J. Wang, M. Ruggenthaler, C. Reichl, W. Wegscheider, A. Rubio, J. Faist, Phys. Rev. X 14, 021038 (2024).
Structured light-matter interactions in materials
Structured light-matter interactions in materials
We are excited about the coupling of quantum materials to structured quantum light, including chiral fields, and the potential of symmetry-broken phases of matter with exotic properties. A special focus is on cavity-induced topology and the corresponding photon-mediated interactions in such systems.
Terahertz chiral photonic-crystal cavities for Dirac gap engineering in graphene, F. Tay, S. Sanders, A. Baydin, Z. Song, D. M. Welakuh, A. Alabastri, V. Rokaj, C. B. Dag, J. Kono. Nature Communications 16, 5270 (2025)
Engineering topology in graphene with chiral cavities, C. B. Dag, V. Rokaj, Physical Review B 110 (12), L121101 (2024)
[Editors' Suggestion].
Polaritonic chemistry
Polaritonic chemistry
We explore the fundamental mechanisms behind the experimentally observed resonant, collective modifications of chemical reactions in polaritonic chemistry. We aim towards a mechanistic understanding of these phenomena, aiming to design cavity inspired protocols for the control of chemistry.
Cavity-mediated collective resonant suppression of local molecular vibrations, V. Rokaj, I. Tutunnikov, H. R. Sadeghpour. The Journal of Physical Chemistry Letters 16 (25), 6249-6258 (2025).
Theory development
Theory development
The group is interested in fundamental problems in quantum electrodynamics (QED), including gauge invariance, renormalization and stability of QED, as well as the fundamental symmetries of the theory. At the same time we develop novel theoretical methods for strongly coupled light-matter systems.
Light–matter interaction in the long-wavelength limit: no ground-state without dipole self-energy, V. Rokaj, D. M. Welakuh, M. Ruggenthaler, A. Rubio, Journal of Physics B: Atomic, Molecular and Optical Physics 51 (3), 034005 (2018).
Quantum Electrodynamical Bloch Theory with Homogeneous Magnetic Fields, V. Rokaj, M. Penz, M. A. Sentef, M. Ruggenthaler, A. Rubio, Physical Review Letters 123 (4), 047202 (2019). [Editors' Suggestion].
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