Highly dispersive magnons with spin-gap-like features in the frustrated ferromagnetic $S=\frac{1}{2}$ chain compound ${\mathrm{Ca}}_2{\mathrm{Y}}_2{\mathrm{Cu}}_5{\mathrm{O}}_{10}$ detected by inelastic neutron scattering

Journal Article · 11 September 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.100.104415 · OSTI ID:1561674

Matsuda, Masaaki  ^[1]; Ma, Jie ^[1]; Garlea, Vasile O.  ^[1]; Ito, T. ^[2]; Yamaguchi, H. ^[2]; Oka, K. ^[2]; Drechsler, S.-L. ^[3]; Yadav, R. ^[3]; Hozoi, L. ^[3]; Rosner, H. ^[4]; Schumann, R. ^[5]; Kuzian, R. O. ^[6]; Nishimoto, S. ^[7]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan)
3. Inst. of Theoretical Solid State Physics, IFW Dresden (Germany)
4. Max-Planck Inst. of Chemical Physics, Dresden (Germany)
5. Inst.of Theoretical Physics, TU Dresden (Germany)
6. Inst. for Problems of Materials Science, NASU, Kiev (Ukraine); Donostia International Physics Center (DIPC), San Sebastian/Donostia (Spain)
7. Inst. of Theoretical Solid State Physics, IFW Dresden (Germany); Inst.of Theoretical Physics, TU Dresden (Germany)

In this paper, we report inelastic neutron scattering experiments in Ca₂Y₂Cu₅O₁₀ and map out the full one-magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO₂ chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio α=|J_a2/J_a1| of the FM NN and the AFM NNN couplings is found as ~0.23, close to the critical point α_c=1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas α_c>0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at ~11.5 and ~28 meV. The gaplike feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on density matrix renormalization group simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution to that gap is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO₂ ones. It gives rise to nonequivalent CuO₄ units and Cu-O-Cu bond angles Φ and a resulting distribution of all exchange integrals. The J's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J₁=24 meV among FFESC cuprates can be explained by a nonuniversal Φ(≠90°) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange $$\overline{K}_{pd}$$~120 meV, similar to a value of 105 meV for Li₂CuO₂, in accord with larger values for La₂CuO₄ and CuGeO₃ (~110 meV) reported by Braden et al. [Phys. Rev. B 54, 1105 (1996)] phenomenologically. Lastly, enhanced $$K_{pd}$$ values are also needed to compensate a significant AFM J_dd ≥ 6 meV from the dd channel, generic for FFESC cuprates but ignored so far.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1561674
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 10 Vol. 100; ISSN 2469-9950; ISSN PRBMDO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English