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| Paper IPM / Physic / 12026 |
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| Abstract: | |||||
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The effects of a magnetic field (h) and a space modulation
(δ) on the magnetic properties of a one-dimensional
antiferromagnetic-ferromagnetic Heisenberg spin-1/2 model have been
studied by means of numerical exact diagonalization of finite size
systems, the nonlinear σ model, and a bosonization approach.
The space modulation is considered on the antiferromagnetic
couplings. At δ = 0, the model is mapped to a gapless
Lüttinger liquid phase by increasing the magnetic field.
However, the space modulation induces a new gap in the spectrum of
the system and the system experiences different quantum phases which
are separated by four critical fields. By opening the new gap, a
magnetization plateau appears at [1/2]Msat. The effects
of the space modulation are reflected in the emergence of a plateau
in other physical functions such as the F-dimer and the bond-dimer
order parameters, and the pair-wise entanglement.
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