Abstract
Spin-phonon coupling (SPC) plays a critical role in numerous intriguing phenomena of transition metal oxides (TMOs). In 3d and 4d TMOs, the coupling between spin and lattice degrees of freedom is known to originate from the exchange interaction. On the other hand, the origin of SPC in 5d TMOs remains to be elucidated. To address this issue, we measured the phonon spectra of the 5d pyrochlore iridate Y2Ir2O7 using optical spectroscopy. Three infrared-active phonons soften below the Néel temperature of TN ≈ 170 K, indicating the existence of strong SPC. Simulations using density functional theory showed that the coupling is closely related to the Ir–O–Ir bond angle. A tight-binding model analysis reveals that this SPC is mainly mediated by the Dzyaloshinskii–Moriya interaction rather than the usual exchange interaction. We suggest that such unconventional SPC may be realized in other 5d TMOs with non-collinear magnetic order.
Highlights
The coupling between various degrees of freedom is an important paradigm in condensed matter physics
To investigate spin-phonon coupling (SPC) with the AIAO magnetic order, we focused on polycrystalline samples of Y2Ir2O7
The experimental σ1(ω) spectra showed several weak peaks, possibly due to impurities,[42] but they did not influence our phonon analysis of Y2Ir2O7
Summary
The coupling between various degrees of freedom (spin, charge, lattice, and orbital) is an important paradigm in condensed matter physics. Such couplings are known to give rise to novel ground states and various emergent phenomena,[1,2,3,4,5] including high TC superconductivity,[2,3] colossal magnetoresistance,[4] etc. It is possible to stabilize a specific magnetic ground state with epitaxial strain[10] or generate magnetoelastic effects by changing the magnetic easy-axis.[7] In this context, it has become increasingly important to develop a detailed understanding of SPC
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