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Ferromagnetically-coupled dimers on the distorted Shastry-Sutherland lattice: Application to (CuCl)LaNb2O7 | | Shunsuke Furukawa
; Tyler Dodds
; Yong Baek Kim
; | | Date: |
26 Apr 2011 | | Abstract: | A recent study [Tassel et al., Phys. Rev. Lett. 105, 167205 (2010)] has
proposed a remarkable spin model for (CuCl)LaNb2O7, in which dimers are
ferromagnetically coupled to each other on the distorted Shastry-Sutherland
lattice. Here, the intra-dimer exchange coupling J>0 is antiferromagnetic,
while the inter-dimer exchange couplings are ferromagnetic and take different
values, J_x,J_y<0, in the two bond directions. Anticipating that the highly
frustrated character of this model may lead to a wide range of behaviors in
(CuCl)LaNb2O7 and related material, we theoretically investigate the ground
state phase diagram of this model in detail using the following three
approaches: a strong-coupling expansion for small J_x and J_y, exact
diagonalization for finite clusters, and a Schwinger boson mean field theory.
When |J_x|, |J_y| <~ J, the system stays in a dimer singlet phase with a finite
spin gap, which is adiabatically connected to the decoupled dimer limit
J_x=J_y=0. We show that the magnetization process of this phase depends
crucially on the spatial anisotropy of the inter-dimer couplings. The
magnetization shows a jump or a smooth increase for weak and strong anisotropy,
respectively, after the spin gap closes at a certain magnetic field. When |J_x|
or |J_y| >~ J, quantum phase transitions to various magnetically ordered phases
(ferromagnetic, collinear stripe, and spiral phases) occur. The Schwinger boson
analysis demonstrates that quantum fluctuations split the classical degeneracy
of different spiral ground states. Implications for (CuCl)LaNb2O7 and related
compounds are discussed in light of our theoretical results and existing
experimental data. | | Source: | arXiv, 1104.5017 | | Services: | Forum | Review | PDF | Favorites | |
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