An unified picture for the Raman response of magnetic excitations in cuprate spin-ladder compounds is obtained by comparing calculated two-triplon Raman line-shapes with those of the prototypical compounds SrCu2O3 (Sr123), Sr14Cu24O41 (Sr14), and La6Ca8Cu24O41 (La6Ca8). The theoretical model for the two-leg ladder contains Heisenberg exchange couplings J and J ⊥ plus an additional four-spin interaction Jcyc. Within this model Sr123 and Sr14 can be described by x := J /J ⊥ = 1.5, xcyc := Jcyc/J ⊥ = 0.2, J Sr123 ⊥ = 1130 cm −1 and J Sr14 ⊥ = 1080 cm −1 . The couplings found for La6Ca8 are x = 1.2, xcyc = 0.2, and J La6Ca8 ⊥ = 1130 cm −1 . The unexpected sharp two-triplon peak in the ladder materials compared to the undoped two-dimensional cuprates can be traced back to the anisotropy of the magnetic exchange in rung and leg direction. With the results obtained for the isotropic ladder we calculate the Raman line-shape of a two-dimensional square lattice using a toy model consisting of a vertical and a horizontal ladder. A direct comparison of these results with Raman experiments for the two-dimensional cuprates R2CuO4 (R=La,Nd), Sr2CuO2Cl2, and YBa2Cu3O 6+δ yields a good agreement for the dominating two-triplon peak. We conclude that short range quantum fluctuations are dominating the magnetic Raman response in both, ladders and planes. We discuss possible scenarios responsible for the high-energy spectral weight of the Raman line-shape, i.e. phonons, the triple-resonance and multi-particle contributions.

We investigated temperature dependent Raman spectra of the one-dimensional spin-ladder compound SrCu2O3. At low temperatures a two-magnon peak is identified at 3160 ± 10 cm −1 and its temperature dependence analyzed in terms of a thermal expansion model. We find that the two-magnon peak position must include a cyclic ring exchange of J cycl /J ⊥ = 0.09 − 0.25 with a coupling constant along the rungs of J ⊥ ≈ 1215 cm −1 (1750 K) in order to be consistent with other experiments and theoretical results. PACS numbers: 78.30.-j, 75.50.Ee O (p x ) Cu (d x²-y² ) J ¡ J J cycl A

This work presents room temperature single crystal X-ray diffraction measurements of the spin ladder compounds SrCu 2 O 3 (Cmmm, a ¼ 3:948ð2Þ A, b ¼ 11:626ð4Þ A, c ¼ 3:509ð1Þ A, Z ¼ 2) and Sr 2 Cu 3 O 5 (Immm, a ¼ 3:395ð2Þ A, b ¼ 3:941ð1Þ A, c ¼ 18:662ð5Þ A, Z ¼ 2), and the evolution of their structures from room temperature down to 100 K. We confirm the structure of SrCu 2 O 3 previously described in the literature from X-ray powder and electron diffraction measurements, and report a new modification for Sr 2 Cu 3 O 5 with an unusual CuO 5 trigonal bipyramidal coordination.

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