Quantum magnet with a helical bond order adjacent to deconfined quantum criticality*

We have numerically discovered that a perturbation preserving the four-fold degeneracy of the VBS order in the JQ model, a 2+1D quantum magnet, creates an intermediate helical phase between the Néel and VBS phases [1]. By weakening the perturbation, the phase shrinks to a deconfined quantum critical (DQC) point [2]. Reconsidering the conventional DQC point as a multicritical point may explain previously observed irregular scalings in DQC [3].
We will introduce methods to characterize the helical phase, e.g., diagonal cylinder boundary conditions to control topological effects, and investigate the possibility of (in-)commensurate transitions within the phase. The helical–VBS transition resembles a chiral helimagnetic transition proposed by Dzyaloshinskii long ago [4], but has only been analyzed beyond mean-field theory recently [5].

[1] B. Zhao, J. Takahashi, and A. W. Sandvik, arXiv: 2005.10184 (2020).
[2] T. Senthil, A. Vishwanath, L. Balents, S. Sachdev, and M. Fisher, Science 303, 1490 (2004).
[3] H. Shao, W. Guo, and A. W. Sandvik, Science 352, 213 (2016).
[4] I. E. Dzyaloshinskii, Sov. Phys. JETP 20, 665 (1965).
[5] Y. Nishikawa and K. Hukushima, Phys. Rev. B 94, 064428 (2016).