Two-dimensional quantum antiferromagnet in a strong magnetic field

Subhankar Khatua, Marcin Raczkowski, Jeroen van den Brink +1 more

Low dimensionality enhances quantum fluctuations, triggering novel states of quantum matter to emerge. In real materials, low dimensionality usually arises from spatially strongly anisotropic couplings. Here, we demonstrate a different mechanism: in two-dimensional systems with coupled alternating ferromagnetic (FM) and antiferromagnetic (AFM) spin-$1/2$ chains, an applied magnetic field may drive a dimensional reduction. Under magnetic field, the FM chains polarize and stiffen, suppressing the propagation of transverse AFM fluctuations from one chain to another, and effectively induce one-dimensional behavior at low energies. For a model describing botallackite, Cu$_2$(OH)$_3$Br, quantum Monte Carlo dynamics show that beyond a critical magnetic field, the low-energy spectrum reduces to that of a one-dimensional AFM Heisenberg spin-$1/2$ chain with field-dependent incommensurate two-spinon fluctuations, providing clear signatures for inelastic neutron scattering.

Subir Sachdev A

Jingyao Meng, Lufeng Zhang, Tianxing Ma +1 more

Using the determinant quantum Monte Carlo method, we investigate the antiferromagnetic phase transition that is induced by the Zeeman field in a disordered interacting two-dimensional Dirac fermion system. At a fixed interaction strength $U$, the antiferromagnetic correlation is enhanced as the magnetic field increases and, when the magnetic field is larger than a ${B}_{c}(U)$, the antiferromagnetic correlation shall be suppressed by the increased magnetic field. The impact of Zeeman field $B$, Coulomb repulsion $U$, and disorder $\mathrm{\ensuremath{\Delta}}$ is not isolated. The intensity of magnetic field effect on the antiferromagnetic correlation shall be strongly suppressed by disorder. Differently, it will be promoted by weak interaction, but, when $U$ becomes larger than ${U}_{c}=4.5$, the increased interaction will suppress the intensity of this effect and here ${U}_{c}=4.5$ coincides with the critical strength inducing the metal-Mott insulator transition in a clean system. Moreover, at a fixed magnetic field $B$, strong interaction shall suppress the antiferromagnetic phase rather than promote it.

Grégoire Misguich, C. Lhuillier

Grégoire Misguich, C. Lhuillier

S. Gluzman

The properties of the one-dimensional antiferromagnet of spin 1/2 in a strong magnetic field h with nearest- and next-nearest-neighbor interactions are studied in terms of the equivalent Bose-gas problem. We find that below the first critical field ${\mathit{h}}_{\mathit{c}\mathit{u}}$ the phase with a gap in the elementary excitations spectrum and corresponding plateau in the magnetization curve should exist due to the two-particle attraction in the vicinity of the commensurate wave number ${\mathit{p}}_{0\mathit{u}}$=\ensuremath{\pi}. In the interval between the first and second critical fields ${\mathit{h}}_{\mathit{c}\mathit{u}}$h${\mathit{h}}_{\mathit{c}\mathit{f}}$, the system behaves as the one-dimensional Bose gas with particle repulsion and the magnetization has a typical square-root dependence on field.