@article{aktersky_syromyatnikov_2016,
title={Low-energy singlet sector in spin-1/2 J_1--J_2 Heisenberg
model on square lattice},
abstractNote={Based on a special variant of plaquette expansion, an operator is constructed
whose eigenvalues give the low-energy singlet spectrum of spin-$\frac12$
Heisenberg antiferromagnet on square lattice with nearest- and frustrating
next-nearest-neighbor exchange couplings $J_1$ and $J_2$. It is well known that
a non-magnetic phase arises in this model at $0.4\lesssim J_2/J_1\lesssim 0.6$
sandwiched by two N\'eel ordered phases. In agreement with previous results, we
observe a first-order quantum phase transition (QPT) at $J_2\approx 0.64J_1$
from the non-magnetic phase to the N\'eel one. Large gap ($\gtrsim0.4J_1$) is
found in the singlet spectrum at $J_2<0.64J_1$ that excludes a gapless
spin-liquid state at $0.4\lesssim J_2/J_1\lesssim 0.6$ and the deconfined
quantum criticality scenario for the QPT to another N\'eel phase. We observe a
first-order QPT at $J_2\approx 0.55J_1$ presumably between two non-magnetic
phases.},
author={Aktersky and Syromyatnikov},
year={2016},
month={May}
}