We have studied the anisotropic three-dimensional nearest-neighbor Ising model with competitive interactions in an uniform longitudinal magnetic field
H. The model consists of ferromagnetic interaction
Jx(Jz) in the
x(z) direction and antiferromagnetic interaction
Jy in the
y direction. We have compared our calculations within a effective-field theory in clusters with four spins (EFT-4) in the simple cubic (sc) lattice with traditional Monte Carlo (MC) simulations. The phase diagrams in the
h−kBT/Jx plane (
h=H/Jx) were obtained for the particular case
λ1=Jy/Jx(λ2=Jz/Jx)=1 (anisotropic sc). Our results indicate second-order frontiers for all values of
H for the particular case
λ2=0 (square lattice), while in case
λ1=λ2=1, we observe first- and second-order phase transitions in the low and high temperature limits, respectively, with presence of a tricritical point. Using EFT-4, a reentrant behavior at low temperature was observed in contrast with results of MC.
Motivated by recent experiments with Rydberg atoms in an optical tweezer array, we accurately map out the ground-state phase diagram of the antiferromagnetic Ising model on a square lattice with longitudinal and transverse magnetic fields using the quantum Monte Carlo method. For a small but nonzero transverse field, the transition longitudinal field is found to remain nearly constant. By scrutinizing the phase diagram, we uncover a narrow region where the system exhibits reentrant transitions between the disordered and antiferromagnetic phases with increasing transverse field. Our phase diagram provides a useful benchmark for quantum simulation of a Rydberg atom system.