Continuous phase transition between Neel and valence bond solid phases in a J-Q-like spin ladder system

We investigate a quantum phase transition between a Neel phase and a valence bond solid (VBS) phase, each of which breaks a different Z(2) symmetry, in a spin-1/2 two-leg XXZ ladder with a four-spin interaction. The model can be viewed as a one-dimensional variant of the celebrated J-Q model on a square lattice. By means of variational uniform matrix product state calculations and an effective field theory, we determine the phase diagram of the model and present evidence that the Neel-VBS transition is continuous and belongs to the Gaussian universality class with the central charge c = 1. In particular, the critical exponents p, n, and, v are found to satisfy the constraints expected for a Gaussian transition within numerical accuracy. These exponents do not detectably change along the phase boundary while they are in general allowed to do so for the Gaussian class.

Automated summary

The study investigates a quantum phase transition between a Neel phase and a valence bond solid (VBS) phase in a spin-1/2 two-leg XXZ ladder with a four-spin interaction. The Neel-VBS transition is found to be continuous and belong to the Gaussian universality class, with critical exponents satisfying expected constraints. These critical exponents do not significantly change along the phase boundary as generally allowed for the Gaussian class.