PHOTOEMISSION SPECTRA OF THE T-J MODEL IN ONE AND 2 DIMENSIONS - SIMILARITIES AND DIFFERENCES

We present an exact diagonalization study of the single-particle spect ral function in the one-dimensional (1D) and two-dimensional (2D) t-J model. By studying the scaling properties with J and t we find a simpl e building pattern in 1D and show that every spectral feature can be u niquely assigned by a spinon and holon momentum. We find two types of low-energy excitations: A band with energy scale J and high spectral w eight disperses upwards in the interior part of the Brillouin zone and reaches E-F at k(F), and a band with energy scale t and low spectral weight disperses downwards in the outer part of the zone, touching E-F at 3k(F). An analogous analysis of the 2D case at half-filling shows that the r band exists also in this case, but is diffuse and never rea ches the Fermi energy. For the doped case in 2D the picture is mon rem iniscent of 1D; in particular, the ''main band'' with a dispersion pro portional to J and the ''shadow band'' with energy scale t can be iden tified also in this case. This leads us to propose that the shadow ban ds discovered by Aebi et al. in Bi2212 are the 2D analog of the 3k(F) singularity in 1D systems and unrelated to antiferromagnetic spin fluc tuations.