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Bridging frustrated-spin-chain and spin-ladder physics: Quasi-one-dimensional magnetism of BiCu2PO6

Alexander A. Tsirlin, Ioannis Rousochatzakis, Deepa Kasinathan, Oleg Janson, Ramesh Nath, Franziska Weickert, Christoph Geibel, Andreas M. Läuchli, and Helge Rosner
Phys. Rev. B 82, 144426 – Published 18 October 2010


We derive and investigate the microscopic model of the quantum magnet BiCu2PO6 using band-structure calculations, magnetic susceptibility and high-field magnetization measurements, as well as exact diagonalization (ED) and density-matrix renormalization group (DMRG) techniques. The resulting quasi-one-dimensional spin model is a two-leg antiferromagnetic ladder with frustrating next-nearest-neighbor couplings along the legs. The individual couplings are estimated from band-structure calculations and by fitting the magnetic susceptibility with theoretical predictions, obtained using full diagonalizations. The nearest-neighbor leg coupling J1, the rung coupling J4, and one of the next-nearest-neighbor couplings J2 amount to 120–150 K while the second next-nearest-neighbor coupling is J2J2/2. The spin ladders do not match the structural chains, and although the next-nearest-neighbor interactions J2 and J2 have very similar superexchange pathways, they differ substantially in magnitude due to a tiny difference in the O-O distances and in the arrangement of nonmagnetic PO4 tetrahedra. An extensive ED study of the proposed model provides the low-energy excitation spectrum and shows that the system is in the strong rung coupling regime. The strong frustration by the next-nearest-neighbor couplings leads to a triplon branch with an incommensurate minimum. This is further corroborated by a strong-coupling expansion up to second order in the inter-rung coupling. Based on high-field magnetization measurements, we estimate the spin gap of Δ32K and suggest the likely presence of antisymmetric Dzyaloshinskii-Moriya anisotropy and interladder coupling J3. We also provide a tentative description of the physics of BiCu2PO6 in magnetic field, in the light of the low-energy excitation spectra and numerical calculations based on ED and DMRG. In particular, we raise the possibility for a rich interplay between one- and two-component Luttinger liquid phases and a magnetization plateau at 1/2 of the saturation value.

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  • Received 12 July 2010


©2010 American Physical Society

Authors & Affiliations

Alexander A. Tsirlin1,*, Ioannis Rousochatzakis2,†, Deepa Kasinathan1, Oleg Janson1, Ramesh Nath1,3, Franziska Weickert1,4, Christoph Geibel1, Andreas M. Läuchli2,‡, and Helge Rosner1

  • 1Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
  • 2Max-Planck-Institut für Physik komplexer Systeme, 01187 Dresden, Germany
  • 3Indian Institute of Science Education and Research, Trivandrum 695016, Kerala, India
  • 4Dresden High Magnetic Field Laboratory, Forschungszentrum Dresden-Rossendorf, 01314 Dresden, Germany

  • *altsirlin@gmail.com
  • rousocha@pks.mpg.de
  • aml@pks.mpg.de

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Vol. 82, Iss. 14 — 1 October 2010

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