Louk Rademaker, Kai Wu, Jan Zaanen
We formulated an effective theory for a single interlayer exciton in a
bilayer quantum antiferro- magnet, in the limit that the holon and doublon are
strongly bound onto one interlayer rung by the Coulomb force. Upon developing a
new linear spin wave approximation of the bilayer Heisenberg model, we
calculated the spectral function of the exciton for a wide range of the
interlayer Heisenberg coupling \alpha=J_{\perp}/Jz. In the disordered phase at
large \alpha, a coherent quasiparticle peak appears representing free motion of
the exciton in a spin singlet background. In the N\'{e}el phase, which applies
to more realistic model parameters, a ladder spectrum arises due to Ising
confinement of the exciton. The exciton spectrum is visible in measurements of
the dielectric function, such as c-axis optical conductivity measurements.
View original:
http://arxiv.org/abs/1202.3616
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