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

摘要

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