Critical properties of a spin-(1/2 chain with competing interactions

The crossover between 2${\mathrm{k}}_{\mathrm{F}}$ and 4${\mathrm{k}}_{\mathrm{F}}$ charge-density waves in an extended one-dimensional Hubbard model is studied in the U→∞ limit by mapping onto a Heisenberg antiferromagnet with a competing second-neighbor Ising interaction. The phase diagram is obtained by a combination of field theory techniques and numerical solution of finite chains. Regions of staggered spin order (4${\mathrm{k}}_{\mathrm{F}}$ site or bond order) and (2,2) spin order (2${\mathrm{k}}_{\mathrm{F}}$ site order) are mapped out. Critical exponents in the algebraic phase are obtained.