Magnon-phonon coupling effects on the indirect K -edge resonant inelastic x-ray scattering spectrum of a two-dimensional Heisenberg antiferromagnet

Abstract

We compute the effects of magnon-phonon coupling on the indirect K-edge bimagnon resonant inelastic x-ray scattering (RIXS) intensity spectrum of a square lattice Heisenberg antiferromagnet. We analyze the effects of competing nearest and next-nearest magnetic and magnon-phonon coupling interaction in the RIXS spectrum, for both the antiferromagnetic (AF) and the collinear antiferromagnetic (CAF) phases of the model. Utilizing the Dyson-Maleev representation of spin operators, the Bethe-Salpeter ladder approximation scheme for the bimagnon interacting channel, and considering the lowest order magnon-phonon-magnon scattering interaction we highlight distinct features in the X-ray spectrum. Considering damping effects, arising due to the presence of phonons, we find that in the AF phase the RIXS intensity spectrum attains a maximum value primarily localized around the K ± π 2 , ± π 2 -point. For the CAF phase the intensity is broadly distributed with a significant scattering intensity located around the Y ± π 2 , 0 -point. Furthermore, in the CAF phase for suitable anisotropy, nearest-, and next-nearest neighbor interaction parameters the phonon effects can manifest itself as a distinct peak both below and above the bimagnon peak. Such a feature is in contrast to the antiferromagnetic spectrum where the effect due to the phonon peak was located consistently beyond the bimagnon peak in the high energy end of the spectrum. Additionally, in the CAF phase we find the RIXS bimagnon-phonon spectrum to be more sensitive to anisotropy compared to its antiferromagnetic counterpart. We conclude that the ultimate effect of magnon-phonon effects in the indirect K-edge RIXS spectrum, in both the antiferromagnetic and the collinear antiferromagnetic phase, is an observable effect. PACS number(s): 78.70.Ck, 75.25.-j, 75.10.Jm cal vibrations) affect the magnetic RIXS spectrum? How can a multimagnon RIXS excitation spectrum, such as that of a bimagnon, be affected by phonons? The interplay of phonons with bimagnons offer the potential to uncover physical phenomena which has been overlooked till date. With next generation beamlines being constructed globally and experimental initiatives likely to probe phonon effects in correlated materials, answers to the above questions are imperative and timely. The theoretical study in this article offers insight on the key experimentally observable signatures which delineate magnon-magnon and magnon-phonon interaction effects in the indirect K-edge RIXS spectrum.Past investigation on spatial anisotropy and significant frustration within the square lattice Heisenberg magnet has led to the prediction of a two-peak bimagnon structure [24]. The proposed two-peak structure was a consequence of the bimagnon spectrum's sensitivity to microscopic magnetic interactions. But, in real materials lattice vibrations do matter. Thus, a realistic theoretical model which provides a true depiction of the materials under investigation with a comprehensive account of magnon-phonon coupling is called for.The coupli...

Dynamic Spin-Lattice Coupling and Nematic Fluctuations in NaFeAs

“…[51], section IV). Similar to the recent calculations on the effect of one-phonon-two-magnon to the indirect K-edge resonant inelastic x-ray scattering spectrum of a 2D Heisenberg antiferromagnet [61], we find that spin waves in 1D chain are also affected by the lattice distortion. In particular, the periodic lattice distortion affect spin waves, which in turn leads to the phonon softening at small q similar to our observation in NaFeAs (Fig.…”

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Detecting Crystallographic Lattice Chirality using Resonant Inelastic X-ray Scattering

“…Experimental [30][31][32][33][34][35][36][37] , theoretical [38][39][40][41][42][43][44][45][46] , and computational [47][48][49][50] investigations have demonstrated that resonant inelastic x-ray scattering (RIXS) spectroscopy can provide a rich source of physics information. Theoretical studies detailing the effects of magnetic frustration 51 , triangular lattice geometry 52 , magnon-phonon coupling 53 , and multi-band excitation 54 of the bimagnon excitation at the K -edge indirect RIXS have been reported. Motivated by the conceptual underpinnings of the aforementioned RIXS studies and the occurence of the chiral 245 class of chalcogenides we investigate the following question -"Can indirect K -edge RIXS spectrosocpy assist with the detection of lattice chirality?"…”

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