Each article includes problems for further study.

M. Karbach and G. Müller

**Introduction to the Bethe ansatz I.**

Computers in Physics 11 (1997), 36-43.
[cond-mat/9809162]

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The Bethe ansatz for the one-dimensional s=1/2
Heisenberg
ferromagnet is introduced at an elementary level. The presentation
follows
Bethe's original work very closely. A detailed description and a
complete
classification of all two-magnon scattering states and two-magnon bound
states are given for finite and infinite chains.

M. Karbach, K. Hu, and G. Müller

**Introduction to the Bethe ansatz II.**

Computers in Physics 12 (1998), 565-573. [cond-mat/
9809163]

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Building on the fundamentals introduced in part I,
we
employ the Bethe ansatz to study some ground-state properties (energy,
magnetization, susceptibility) of the one-dimensional s=1/2 Heisenberg
antiferromagnet in zero and nonzero magnetic field. The 2-spinon
triplet
and singlet excitations from the zero-field ground state are discussed
in detail, and their energies are calculated for finite and infinite
chains.
Procedures for the numerical calculation of real and complex solutions
of the Bethe ansatz equations are discussed and applied.

M. Karbach, K. Hu, and G. Müller

**Introduction to the Bethe ansatz III.**

[cond-mat/ 0008018]

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Having introduced the magnon in part I and the spinon in part II as the relevant quasi-particles for the interpretation of the spectrum of low-lying excitations in the one-dimensional (1D) s=1/2 Heisenberg ferromagnet and antiferromagnet, respectively, we now study the low-lying excitations of the Heisenberg antiferromagnet in a magnetic field and interpret these collective states as composites of quasi-particles from a different species. We employ the Bethe ansatz to calculate matrix elements and show how the results of such a calculation can be used to predict lineshapes for neutron scattering experiments on quasi-1D antiferromagnetic compounds.