Far-infrared spectroscopy of spin excitations and Dzyaloshinskii-Moriya interactions in a Shastry-Sutherland compound SrCu${}_2$(BO${}_3$)$_2

Abstract

We have studied spin excitation spectra in the Shastry-Sutherland model compound SrCu${}_2$(BO${}_3$)${}_2$ in magnetic fields using far-infrared Fourier spectroscopy. The transitions from the ground singlet state to the triplet state at 24 cm${}^{-1}$ and to several bound triplet states are induced by the electric field component of the far-infrared light. To explain the light absorption in the spin system we invoke a dynamic Dzyaloshinskii-Moriya (DM) mechanism where light couples to a phonon mode, allowing the DM interaction. Two optical phonons couple light to the singlet to triplet transition in SrCu${}_2$(BO${}_3$)${}_2$. One is $a$-polarized and creates an intra-dimer dynamic DM along the c axis. The other is $c$-polarized and creates an intra-dimer dynamic DM interaction, it is in the $(ab)$ plane and perpendicular to the dimer axis. Singlet levels at 21.5 and 28.6 cm${}^{-1}$ anti-cross with the first triplet as is seen in far-infrared spectra. We used a cluster of two dimers with a periodic boundary condition to perform a model calculation with scaled intra- and inter-dimer exchange interactions. Two static DM interactions are sufficient to describe the observed triplet state spectra. The static inter-dimer DM in the c-direction $d_1=0.7$ cm${}^{-1}$ splits the triplet state sub-levels in zero field [Cépas et al., Phys. Rev. Lett. \textbf{87}, 167205 (2001)]. The static intra-dimer DM in the $(ab)$ plane (perpendicular to the dimer axis) $d_2=1.8$ cm${}^{-1}$, allowed by the buckling of CuBO${}_3$ planes, couples the triplet state to the 28.6 cm${}^{-1}$ singlet as is seen from the avoided crossing.

12 pages with 7 figures, some references corrected

References in corpus (17)

• Magnetic Superstructure in the Two-Dimensional Quantum Antiferromagnet SrCu2(BO3)2
• Quantum Phase Transitions in the Shastry-Sutherland Model for $\mathbf{SrC}{\mathbf{u}}_2(\mathbf{B}{\mathbf{O}}_3{)}_2$
• Direct Evidence for the Localized Single-Triplet Excitations and the Dispersive Multi-Triplets Excitations in SrCu2(BO3)2
• Dispersion and Symmetry of Bound States in the Shastry-Sutherland Model
• Direct observation of the multiple spin gap excitations in two-dimensional dimer system SrCu2(BO3)2
• Dzyaloshinski-Moriya Interaction in the 2D Spin Gap System SrCu2(BO3)2
• Phase Diagram of the quadrumerized Shastry-Sutherland Model
• Quantum Phases of the Shastry-Sutherland Antiferromagnet
• Collective Singlet Excitations and Evolution of Raman Spectral Weights in the 2D Spin Dimer Compound SrCu2(BO3)2
• ESR study on the excited state energy spectrum of SrCu${}_2$(BO${}_3$)${}_2$ -a central role of multiple-triplet bound states
• Dynamic Structure Factor of the Two-Dimensional Shastry-Sutherland Model
• X-Band ESR Determination of Dzyaloshinsky-Moriya Interaction in 2D SrCu${}_2$(BO${}_3$)${}_2$ System
• Structural Phase Transition in the 2D Spin Dimer Compound SrCu2(BO3)2
• Far infrared study of the two dimensional dimer spin system SrCu_2(BO_3)_2
• Low energy excitations and dynamic Dzyaloshinskii-Moriya interaction in ${\alpha }^{\prime }$-NaV${}_2$O${}_5$ studied by far infrared spectroscopy
• Theory of phonon-assisted "forbidden" optical transitions in spin-gapped systems
• The Stochastic State Selection Method for Energy Eigenvalues in the Shastry-Sutherland Model

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• Microscopic mechanisms of spin-dependent electric polarization in 3d oxides
• Dzyaloshinsky-Moriya antisymmetric exchange coupling in cuprates: Oxygen effects
• Magnon Dispersion and Anisotropies in SrCu${}_2$(BO${}_3$)${}_2$
• Symmetry and light coupling to phononic and collective magnetic excitations in SrCu_2(BO_3)_2
• High-field spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8
• Quantum criticality with emergent symmetry in the extended Shastry-Sutherland model
• Fractional magnetization plateaux of a spin-1/2 Heisenberg model on the Shastry-Sutherland lattice: effect of quantum XY interdimer coupling
• Effects of staggered Dzyaloshinskii-Moriya interactions in a quasi-two-dimensional Shastry-Sutherland model
• Magneto-optic far-infrared study of Sr${}_{14}$Cu${}_{24}$O${}_{41}$: triplet excitations in chains
• Triplons, triplon pairs and dynamical symmetries in laser-driven Shastry-Sutherland magnets
• Triplet excitations in the frustrated spin ladder Li${}_2$Cu${}_2$O(SO${}_4$)${}_2$
• Anomalous magnetic exchange in a dimerized quantum-magnet composed of unlike spin species
• Effects of Ca substitution on quasi-acoustic sliding modes in Sr${}_{14-x}$Ca${}_x$Cu${}_{24}$O${}_{41}$