Squeezed strings and Yangian symmetry of the Heisenberg chain with long-range interaction

The exact and complete set of highest-weight eigenstates of the finite-size SU(n) Heisenberg chain with inverse-square exchange (ISE) are constructed using the occupation-number representation of the ''strings,'' which can be considered as the unbroken resonating-valence bonds. The string description, which is believed to be exact only in the thermodynamic limit for the Bethe ansatz solvable models, becomes exact for any size ISE model due to the squeezing effect of the strings in the ISE limit. This feature provides a basis for the realization of the Yangian symmetry in the ISE model.