Dynamics of an SO(5)-symmetric ladder model

We discuss properties of a recently proposed exactly SO(5)-symmetric ladder model. In the strong coupling limit we demonstrate how the SO(3)-symmetric description of spin ladders in terms of bond bosons can be upgraded to an SO(5)-symmetric bond-boson model, which provides a particularly simple exam ple for the concept of SO(5) symmetry. Based on this representation we show that antiferromagnetism and superconductivity can be understood as condens ation of either magnetic or charged bosons into a resonating-valence-bond v acuum. We identify exact eigenstates of a finite cluster with general multi plets of the SO(5) group, and present numerical results for the single part icle, spin and charge spectra of the SO(5)-symmetric model and identify "fi ngerprints" of SO(5) symmetry in these. In particular we show that SO(5) sy mmetry implies a "generalized rigid band behavior" of the photoemission spe ctrum, i.e., spectra for the doped case are rigorously identical to spectra for spin-polarized states at half filling. [S0163-1829(98)06945-8].