Circular Dichroism in Resonant Inelastic X-ray Scattering: Probing Altermagnetic Domains in MnTe

Abstract

X-ray magnetic circular dichroism provides a means to identify ferromagnetic, chiral, and altermagnetic orders via their time-reversal-symmetry ($\mathcal{T}$) breaking. However, differentiating magnetic domains related by crystallographic symmetries remains a technical challenge. Here we reveal a circular dichroism (CD) in the resonant inelastic x-ray scattering (RIXS) spectra from the altermagnetic MnTe. The azimuthal dependence of the RIXS-CD intensity of the magnon excitations indicates a dominant occupation of a single altermagnetic domain. The RIXS-CD in our scattering geometry is ascribed to the mirror-symmetry breaking associated with the $\mathcal{T}$-broken altermagnetic order. Our results establish RIXS-CD as a domain-sensitive probe of elementary excitations in quantum materials.

Figures (3)

• Figure 1: (a) Altermagnetic order in MnTe and the scattering geometry of the resonant inelastic x-ray scattering (RIXS) experiment. The orange (blue) spiral depicts the incoming (outgoing) circularly polarized x-ray photons. $\theta_i$ denotes the angle between the incoming beam and the sample surface, $2\theta$ is the scattering angle, and the azimuthal angle $\phi$ generates the rotation of the scattering plane about the sample normal. A small magnetic field of $B=$ 0.25 T is applied along the c axis to stabilize the depicted altermagnetic domain. (b) Possible six altermagnetic domains. Domains 1-3 are $\mathcal{T}$-equivalent domains related by the $C_3$ rotation, and domains 4-6 are their $\mathcal{T}$-counterparts. The dotted lines on domain 1 indicate the mirror planes ($\mathcal{M}$) of the normal state. (c) Mn $L_{2,3}$-edge x-ray absorption (XAS) spectra collected with total fluorescence yield (TFY) mode using the right (CR) and left (CL) circularly-polarized light. The blue curve shows the x-ray magnetic circular dichroism (XMCD) signal. The green curve shows the theoretical XMCD spectrum Hariki.A_etal.Phys.-Rev.-Lett.2024.
• Figure 2: (a), (b) Low-energy RIXS spectra of MnTe collected along the ${\bm q}=(H, 0, -0.5)$ and ${\bm q}=(0, 0, L)$ directions. The data were collected with $\pi$-polarized photons with $h\nu=$ 641.1 eV. Three Voigt profiles represent the elastic, magnon (red), and two-magnon excitations. (c), (d) Transverse component of the spin dynamical structure factor $S({\bm q}, \omega)=(S^{yy}+S^{zz})({\bm q}, \omega)$. The experimental magnon peak energies are plotted as red circles.
• Figure 3: (a)-(c) RIXS spectra collected with right and left circularly polarized light, at the azimuthal angles $\phi=0^\circ$, $30^\circ$, and $60^\circ$, respectively. RIXS-CD intensity defined as their difference is also shown. The curves in the second and third rows are the corresponding theoretical RIXS and RIXS-CD spectra for the domain 1 computed with the spin wave and Anderson impurity model (AIM) methods. The bottom curves show the fit of the experimental curves as superpositions of the theoretical AIM spectra for the domains 1-3.