The recent progress in the optimization of two-dimensional tensor
networks [H.-J. Liao, J.-G. Liu, L. Wang, and T. Xiang, Phys. Rev. X 9,
031041 (2019)] based on automatic differentiation opened the way towards
precise and fast optimization of such states and, in particular,
infinite projected entangled-pair states (iPEPS) that constitute a
generic-purpose Ansatz for lattice problems governed by local Hamiltonians.
In this work, we perform an extensive study of a paradigmatic model of
frustrated magnetism, the J_1-J_2J1−J2
Heisenberg antiferromagnet on the square lattice. By using advances in
both optimization and subsequent data analysis, through finite
correlation-length scaling, we report accurate estimations of the
magnetization curve in the N'eel phase for
J_2/J_1 \le 0.45J2/J1≤0.45.
The unrestricted iPEPS simulations reveal an
U(1)U(1)
symmetric structure, which we identify and impose on tensors, resulting
in a clean and consistent picture of antiferromagnetic order vanishing
at the phase transition with a quantum paramagnet at
J_2/J_1 \approx 0.46(1)J2/J1≈0.46(1).
The present methodology can be extended beyond this model to study
generic order-to-disorder transitions in magnetic systems.