Effect of spin gap on single-hole excitation spectrum in the one-dimensional t-J-J ' model

We examine the effect of spin gap on single-hole spectral function in the o ne-dimensional t-J-J' model. At J'/J = 1/2, where a dimer state is the grou nd state, an analytic expression is derived for J/t --> 0. At finite values of J/t, the numerical diagonalizations for finite-size clusters are perfor med. In contrast to the gapless case, we find that (i) the dispersion becom es symmetric around k = pi/2, (ii) the singularity of the holon band is str ongly suppressed, and (iii) the quasi-particle weight Z(h) becomes finite a t finite J/t. The feature (iii) is related to the presence of a bound state of the doped hole and an unpaired spin. (C) 1998 Elsevier Science Ltd. All rights reserved.