arXiv:cond-mat/0009402 · Journal of Physics Condensed Matter

Symmetries and triplet dispersion in a modified Shastry-Sutherland model for SrCu2(BO3)2

Christian Knetter, Erwin Müller-Hartmann, Götz Silvester Uhrig, Erwin Müller-Hartmann

Published Oct 5, 2000• 15 citations

Abstract

We investigate the one-triplet dispersion in a modified Shastry-Sutherland model for SrCu 2 (BO 3 ) 2 by means of a series expansion about the limit of strong dimerization. Our perturbative method is based on a continuous unitary transformation that maps the original Hamiltonian to an effective, energy-quanta-conserving block diagonal Hamiltonian eff . The dispersion splits into two branches which are nearly degenerate. We analyse the symmetries of the model and show that space group operations are necessary to explain the degeneracy of the dispersion at k = 0 and at the border of the magnetic Brillouin zone. Moreover, we investigate the behaviour of the dispersion for small | k | and compare our results to inelastic neutron scattering data.

DOI: 10.1088/0953-8984/12/42/312

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arXiv:cond-mat/0009402 · Journal of Physics Condensed Matter

Symmetries and triplet dispersion in a modified Shastry-Sutherland model for SrCu2(BO3)2

Christian Knetter, Erwin Müller-Hartmann, Götz Silvester Uhrig, Erwin Müller-Hartmann

Published Oct 5, 2000• 15 citations

arXiv HTML PDF

Abstract

DOI: 10.1088/0953-8984/12/42/312

Related papers

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({J}_{2}/{J}_{1}{)}^{14}

] permit one to fix the parameters of

{\mathrm{SrCu}}_{2}({\mathrm{BO}}_{3}{)}_{2}

precisely:

{J}_{1}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}6.16(10)\mathrm{meV}

, $x\ensuremath{\mathrel{:=}}{J}_{2}/{J}_{1}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.603(3)$, ${J}_{\ensuremath{\perp}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.3(2)\mathrm{meV}$. At the border of the magnetic Brillouin zone a general double degeneracy is derived. An unexpected instability in the triplet channel at

x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.63

indicates a transition towards another phase. The possible nature of this phase is discussed.

Magnetization plateaus in the Shastry-Sutherland model for

{\rm SrCu_2(BO_3)_2}

are studied by the perturbation expansion method. The fourth-order effective Hamiltonian which describes the dynamics of triplet dimers (TD's) with

S^{\rm tot}_z=1

in the singlet sea is derived and then partially diagonalized for the space that consists of the TD configurations with the lowest second-order energy. The fourth-order terms are treated within a low-density approximation. Our procedure makes clear how TD interactions are responsible for the formation of magnetization plateaus. Particularly, the 1/4-plateau is obtained by the fourth-neighbor TD repulsion in the fourth-order perturbation, and a diagonal stripe arrangement of TD's appears at this plateau.