Zero-temperature magnetic-field-induced phase transition between two ordered gapped phases in spin-ladders with ferromagnetic legs

TL;DR

This paper proposes a new magnetic-field-induced phase transition scenario in ferromagnetic-leg spin ladders, where the system transitions directly to a fully polarized phase without passing through an incommensurate phase, with a finite spin gap at the transition.

Contribution

It introduces a novel transition scenario in ferromagnetic-leg spin ladders supported by an exactly solvable model, suggesting a direct transition to a ferromagnetic phase.

Findings

Finite spin gap at the transition point.

Direct transition to ferromagnetic phase without incommensurate phase.

Application to the material (5IAP)_2CuBr_4*H_2O.

Abstract

We suggest that under an increase of a magnetic field a spin-ladder with ferromagnetic legs does not pass without fail through an incommensurate phase but possibly in a straight way turns into a fully polarized ferromagnetic phase. The spin gap remains finite at the transition point. This scenario is demonstrated for the special spin-ladder model with exact singlet-rung ground state. We suppose that this kind of behavior realizes for the spin-ladder material (5IAP)_2CuBr_4*H_2O