Vacancy-induced spin texture in a one-dimensional S=1/2 Heisenberg antiferromagnet

We study the effect of a missing spin in a one-dimensional S = 1/2 antiferromagnet with nearest-neighbor Heisenberg exchange J and six-spin coupling Q = 4qJ using quantum Monte-Carlo (QMC) and bosonization techniques. For q < q(c) approximate to 0.04, the system is in a quasilong range ordered power-law antiferromagnetic phase, which gives way to a valence-bond solid state that spontaneously breaks lattice translation symmetry for q > q(c). We study the ground-state spin texture Phi (r) = < G(up arrow)vertical bar S(z)(r)vertical bar G(up arrow)> in the the S(tot)(z) = 1/2 ground state vertical bar G(up arrow)vertical bar of the system with a missing spin, focusing on the alternating part N(z) (r). We find that our QMC results for N(z) at q = q(c) take on the scaling form expected from bosonization considerations, but violate scaling for q < q(c). Within the bosonization approach, such violations of scaling arise from the presence of a marginally irrelevant sine-Gordon interaction, whose effects we calculate using renormalization group (RG) improved perturbation theory. Our field-theoretical predictions are found to agree well with the QMC data for q < q(c).