Johannes Feist
Department of Theory of Condensed Matter Physics, Universidad Autonoma de Madrid, Spain
Using cavities to modify material properties
When: 12:00-13:00 CET, April 25th (Thursday), 2024
Where: Seminar Room (182), ICMM-CSIC, Campus de Cantoblanco, Madrid
The use of cavity quantum electrodynamical effects, i.e., of vacuum electromagnetic fields, to modify material properties has rapidly gained popularity and interest in the last decade. A canonical example of this is strong light-matter coupling, reached when the interaction of material excitations with confined light modes overcomes dissipation effects and the two parts hybridize to form mixed light-matter eigenstates, so-called polaritons. These polaritons inherit properties of both light and matter excitations and additionally display fundamentally new phenomena. The large range of possible material systems and cavity architectures opens a rich playground for novel functionalities. In the talk, I will discuss several topics related to this overall field, including the modification and photophysics and photochemistry in organic molecules, some fundamental results and pitfalls for the modification of low-energy excitations, and recent progress on few-mode field quantization in complex nanophotonic structures, i.e., strategies to obtain the construction of cavity-QED-like models for arbitrary cavity geometries and materials.
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Ricardo Lobo
ESPCI Paris – PSL University – CNRS – Sorbonne Université, France
Correlations and dispersive Dirac physics in the quantum material family BaCoS2-BaNiS2 – Reverse band-structure engineering of the optical conductivity
When: 12:00-13:00 CET, May 30th (Thursday), 2024
Where: Seminar Room (182), ICMM-CSIC, Campus de Cantoblanco, Madrid
BaCoS2 and BaNiS2 are the end members of a solid solution that shows a vast array of quantum properties. The Co material is close to a strongly correlated insulator with an antiferromagnetic transition, as well as a structural phase transition, around room temperature. At 28% Ni doping this material undergoes an electronic metal-insulator phase transition to a Drude metal. The metallic state persists all the way to the pure Ni compound. At this point, in addition to a Drude peak, we observe a strong contribution from bands with linear dispersion at the Fermi level, which give origin to dispersive Dirac nodal lines. We measured the optical conductivity of these materials and combined them with ab-initio calculations to reverse engineer the role of each band in the physical response of these materials. We explained uncommon features in their optical response such as a linear dispersion of the optical conductivity [1] and the existence of an isosbestic line separating a spectral-weight transfer across Dirac nodal states [2].
[1] D. Santos-Cottin, Y. Klein, P. Werner, T. Miyake, L. de’Medici, A. Gauzzi, R.P.S.M. Lobo, and M. Casula, Linear behavior of the optical conductivity and incoherent charge transport in BaCoS2, Phys. Rev. Materials 2, 105001 (2018). arXiv: 1712.01539.
[2] D. Santos-Cottin, M. Casula, L. de’Medici, F. Le Mardelé, J. Wyzula, M. Orlita, Y. Klein, A. Gauzzi, A. Akrap, and R.P.S.M. Lobo, Optical conductivity signatures of open Dirac nodal lines, Phys. Rev. B 104, L201115 (2021). arXiv: 2104.05521.