Singlet quantum phases and magnetization of the frustrated spin-1/2 ladder with ferromagnetic (F) exchange in legs and alternating F-AF exchange in rungs

TL;DR

This paper investigates the quantum phases and magnetization behavior of a frustrated spin-1/2 ladder with specific ferromagnetic and antiferromagnetic exchanges, revealing three distinct singlet phases with unique magnetic transitions.

Contribution

It characterizes three singlet quantum phases in a frustrated spin ladder with ferromagnetic and alternating exchanges, detailing their magnetization properties and phase connections.

Findings

Identified three singlet quantum phases with distinct magnetization behaviors.

Discovered a first-order transition at saturation field in the Dimer phase.

Established adiabatic connections to known spin chain models.

Abstract

The magnetization $M(h)$ is used to identify three singlet quantum phases of the ladder with isotropic exchange interactions. The Dimer phase with frustrated F exchanges in rungs and legs has a first-order $M(h)$ transition at $0$ K from singlet to ferromagnetic at the saturation field $h_s$. The Haldane-DAF phase with strong F exchange in rungs and net AF exchange between rungs has continuous $M(h)$ and is adiabatically connected to the $S = 1$ Heisenberg AF chain. The AF phase with strong F exchange in legs and net AF exchange between legs has continuous $M(h)$ and is adiabatically connected to the spin-1/2 $J_1-J_2$ model with $J_1 > 0$ and $J_2 < 0$. All three singlet phases have finite gaps to the lowest triplet state.