Journal of Physics Conference Series

Two-step quantum spin flop transition in spin ladders

Tôru Sakai, Kazuki Okamoto, Takashi Tonegawa

Published Mar 1, 2009• 2 citations

Abstract

The magnetization process of the S = 1/2 spin ladder system with ferromagnetic rung exchange interaction is investigated by the numerical exact diagonalization of finite-size clusters. It is found that in the presence of an easy-axis anisotropy the system exhibits a two-step field induced phase transition corresponding to the spin flop. Due to large quantum fluctuation, each step is a second-order transition and the second step occurs between two different Tomonaga-Luttinger liquid phases. Some phase diagrams are also presented.

DOI: 10.1088/1742-6596/150/4/042169

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Journal of Physics Conference Series

Two-step quantum spin flop transition in spin ladders

Tôru Sakai, Kazuki Okamoto, Takashi Tonegawa

Published Mar 1, 2009• 2 citations

Publisher

Abstract

DOI: 10.1088/1742-6596/150/4/042169

Related papers

Field-induced spin nematic Tomonaga-Luttinger liquid of the S=12 spin ladder system with anisotropic ferromagnetic rung interaction

Tôru Sakai, Ryosuke Nakanishi, Takaharu Yamada +5 more

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AIP AdvancesFeb 1, 20260 citations

The

S=\frac{1}{2}

quantum spin ladder system with the anisotropic ferromagnetic exchange interaction on the rung under magnetic field is investigated using the numerical diagonalization and the density matrix renormalization group (DMRG) analyses. It is found that the nematic-spin-correlation-dominant Tomonaga-Luttinger liquid (TLL) appears in some high magnetic field. It is included in the TLL phase where the two-magnon bound state is realized. For some suitable parameters, after the field-induced phase transition from this two-magnon-bound TLL phase to the single-magnon TLL one, the re-entrant transition to the two-magnon-bound TLL phase occurs, which is confirmed by the magnetization curves by the DMRG. Several phase diagrams on the plane of the coupling anisotropy versus the magnetization and the magnetic field are presented. The present result is a proposal of the candidate system which exhibits the spin nematic phase without the biquadratic interaction or the frustration.

Field-Induced Spin Nematic Phase in the

S=1

Anisotropic Spin Ladder

Translational Symmetry Broken Magnetization Plateau of the

S={{1}\over{2}}

Anisotropic Spin Ladder with Ferromagnetic Rung Interaction

The magnetization process of the

S=1/2

anisotropic spin ladder with the ferromagnetic rung interaction is investigated using the numerical diagonalization of finite-size clusters. It is found that the translational symmetry broken magnetization plateau would appear at half the saturation magnetization, when the competing anisotropies are sufficiently large. The phase diagram with respect to the anisotropies and several magnetization curves are presented.

We explore the ground-state phase diagram of the

S=1/2

two-leg ladder with different leg interactions. The

xy

and

z

components of the leg interactions between nearest-neighbor spins in the

a

(

b

) leg are respectively denoted by

J_{{\rm l},a}

and

Δ_{\rm l} J_{{\rm l},a}

(

J_{{\rm l},b}

and

Δ_{\rm l} J_{{\rm l},b}

). On the other hand, the

xy

and

z

components of the uniform rung interactions are respectively denoted by

Γ_{\rm r} J_{\rm r}

and

J_{\rm r}

. In the above,

Δ_{\rm l}

and

Γ_{\rm r}

are the

XXZ

-type anisotropy parameters for the leg and rung interactions, respectively. This system has a frustration when

J_{{\rm l},a} J_{{\rm l},b}<0

irrespective of the sign of

J_{\rm r}

. The phase diagram on the

Δ_{\rm l}

(

|Δ_{\rm l}| \leq 1.0

) versus

J_{{\rm l},b}

(

-2.0\leq J_{{\rm l},b}\leq 3.0

) plane in the case where

J_{{\rm l},a}=0.2

J_{\rm r}=-1.0

, and

Γ_{\rm r} = 0.5

is determined numerically. We employ the physical consideration, and the level spectroscopy and phenomenological renormalization-group analyses of the numerical date obtained by the exact diagonalization method. The resultant phase diagram contains the ferromagnetic, Haldane, N{é}el, nematic Tomonaga-Luttinger liquid (TLL), partial ferrimagnetic, and

XY1

phases. Interestingly enough, the nematic TLL phase appears in the strong-rung unfrustrated region as well as in the strong-rung frustrated one. We perform the first-order perturbational calculations from the strong rung coupling limit to elucidate the characteristic features of the phase diagram. Furthermore, we make the density-matrix renormalization-group calculations for some physical quantities such as the energy gaps, the local magnetization, and the spin correlation functions to supplement the reliability of the phase diagram.