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arXiv · 2608.29566

Extreme Polarization of the Optical Gap and High-Energy Exciton Landscape in CrSBr

Sayantan Patra·Sourabh Jain·Bhumika Chauhan·Marie-Christin Heißenbüttel·Abhisek Saidarsan·Ranjuna M. K.·Kseniia Mosina·Zdeněk Sofer·Michael Rohlfing·Thorsten Deilmann·Ashish Arora
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Abstract

We reveal a strongly anisotropic excitonic landscape in monolayer and bulk-like CrSBr using optical absorption spectroscopy and $GW$-Bethe-Salpeter equation $\textit{ab initio}$ calculations. The direct absorptive determination of the lowest bright optical onsets i.e. $X_0^a$ and $X_0^b$ excitons for the two in-plane polarization eigenaxes yield an in-plane optical gap anisotropy of $470 \pm 15$ meV. This is the highest observed value for any material in the near-infrared-to-visible spectral region to the best of our knowledge. Energetically above, we identify multiple strongly polarized excitons spanning $1.25$ eV to $3.1$ eV selectively aligned along the two orthogonal axes. A resonance $X^-$, located $24$ meV below the $X_0^b$ progressively transfers oscillator strength to $X_b^0$, a behavior consistent with a coupled trion (Fermi-polarion)/exciton pair. Our experiments also provide polarization-resolved broadband dielectric functions of CrSBr. These results establish CrSBr as a strongly polarization-selective excitonic system and highlight its potential for polarization-selective optoelectronics enabled with its large optical-gap anisotropy.

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Sayantan Patra, Sourabh Jain, Bhumika Chauhan, Marie-Christin Heißenbüttel, Abhisek Saidarsan, Ranjuna M. K., Kseniia Mosina, Zdeněk Sofer, Michael Rohlfing, Thorsten Deilmann, Ashish Arora. 2026-08-30. Extreme Polarization of the Optical Gap and High-Energy Exciton Landscape in CrSBr. https://arxiv.org/abs/2608.29566

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