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arXiv · 2501.16034

Circular dichroism in resonant inelastic x-ray scattering from birefringence in CuO

Abhishek Nag·Gérard Sylvester Perren·Hiroki Ueda·A. T. Boothroyd·D. Prabhakaran·M. García-Fernández·S. Agrestini·Ke-Jin Zhou·Urs Staub
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Abstract

Resonant inelastic x-ray scattering (RIXS) has become a prominent technique to study quasiparticle excitations. With advances in polarization analysis capabilities at different facilities, RIXS offers exceptional potential for investigating symmetry-broken quasiparticles like chiral phonons and magnons. At optical wavelengths birefringence can severely affect polarization states in low-symmetry systems. Here we show its importance for soft x-ray resonances. Given the growing interest in Circular Dichroism (CD) in RIXS, it is important to evaluate how birefringence may affect the RIXS spectra of anisotropic systems. We investigate CuO, a well-known anisotropic material, using Cu $L_3$-edge RIXS and detect significant CD in both magnetic and orbital excitations in the collinear antiferromagnetic phase. We demonstrate that the CD can be modeled by a proper treatment of RIXS scattering amplitudes derived from single-ion calculations with birefringence. Recognizing these effects is crucial for unambiguous identification of subtle dichroic effects induced by symmetry-broken quasiparticles. Furthermore, the combined sensitivity of RIXS and birefringence to local symmetry presents an opportunity to study microscopic changes driven by external perturbations.

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Abhishek Nag, Gérard Sylvester Perren, Hiroki Ueda, A. T. Boothroyd, D. Prabhakaran, M. García-Fernández, S. Agrestini, Ke-Jin Zhou, Urs Staub. 2025-01-27. Circular dichroism in resonant inelastic x-ray scattering from birefringence in CuO. https://doi.org/10.1103/physrevresearch.7.l022047

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