We investigate the low-temperature phase diagram of the exactly solved su (4) two-leg spin ladder as a function of the rung coupling and magnetic field H by means of the thermodynamic Bethe ansatz (TBA). In the absence of a magnetic field the model exhibits three quantum phases, while in the presence of a strong magnetic field there is no singlet ground state for ferromagnetic rung coupling. For antiferromagnetic rung coupling, there is a gapped phase in the regime H < H c1 , a fully polarized gapped phase for H > H c2 and a Luttinger liquid magnetic phase in the regime H c1 < H < H c2 . The critical behaviour derived using the TBA is consistent with the existing experimental, numerical and perturbative results for the strong coupling ladder compounds. This includes the spin excitation gap and the critical fields H c1 and H c2 , which are in excellent agreement with the experimental values for the known strong coupling ladder compounds (5IAP) 2 CuBr 4 ·2H 2 O, Cu 2 (C 5 H 12 N 2 ) 2 Cl 4 and (C 5 H 12 N) 2 CuBr 4 . In addition we predict the spin gap for the weak coupling compounds with , such as (VO) 2 P 2 O 7 , and also show that the gap opens for arbitrary .We investigate the low-temperature phase diagram of the exactly solved su (4) two-leg spin ladder as a function of the rung coupling and magnetic field H by means of the thermodynamic Bethe ansatz (TBA). In the absence of a magnetic field the model exhibits three quantum phases, while in the presence of a strong magnetic field there is no singlet ground state for ferromagnetic rung coupling. For antiferromagnetic rung coupling, there is a gapped phase in the regime H < H c1 , a fully polarized gapped phase for H > H c2 and a Luttinger liquid magnetic phase in the regime H c1 < H < H c2 . The critical behaviour derived using the TBA is consistent with the existing experimental, numerical and perturbative results for the strong coupling ladder compounds. This includes the spin excitation gap and the critical fields H c1 and H c2 , which are in excellent agreement with the experimental values for the known strong coupling ladder compounds (5IAP) 2 CuBr 4 ·2H 2 O, Cu 2 (C 5 H 12 N 2 ) 2 Cl 4 and (C 5 H 12 N) 2 CuBr 4 . In addition we predict the spin gap for the weak coupling compounds with , such as (VO) 2 P 2 O 7 , and also show that the gap opens for arbitrary .

arXiv:cond-mat/0305633New Journal of PhysicsAug 11, 200312 citations

Exact Results for the Thermal and Magnetic Properties of Strong Coupling Ladder Compounds

Murray T. Batchelor, Xi-Wen Guan, N. Oelkers +3 more

We investigate the thermal and magnetic properties of the integrable $su(4)$ ladder model by means of the quantum transfer matrix method. The magnetic susceptibility, specific heat, magnetic entropy, and high field magnetization are evaluated from the free energy derived via the recently proposed method of high temperature expansion for exactly solved models. We show that the integrable model can be used to describe the physics of the strong coupling ladder compounds. Excellent agreement is seen between the theoretical results and the experimental data for the known ladder compounds $(5\mathrm{I}\mathrm{A}\mathrm{P}{)}_{2}{\mathrm{C}\mathrm{u}\mathrm{B}\mathrm{r}}_{4}\ifmmode\cdot\else\textperiodcentered\fi{}2{\mathrm{H}}_{2}\mathrm{O}$, ${\mathrm{C}\mathrm{u}}_{2}({\mathrm{C}}_{5}{\mathrm{H}}_{12}{\mathrm{N}}_{2}{)}_{2}{\mathrm{C}\mathrm{l}}_{4}$ , etc.We investigate the thermal and magnetic properties of the integrable $su(4)$ ladder model by means of the quantum transfer matrix method. The magnetic susceptibility, specific heat, magnetic entropy, and high field magnetization are evaluated from the free energy derived via the recently proposed method of high temperature expansion for exactly solved models. We show that the integrable model can be used to describe the physics of the strong coupling ladder compounds. Excellent agreement is seen between the theoretical results and the experimental data for the known ladder compounds $(5\mathrm{I}\mathrm{A}\mathrm{P}{)}_{2}{\mathrm{C}\mathrm{u}\mathrm{B}\mathrm{r}}_{4}\ifmmode\cdot\else\textperiodcentered\fi{}2{\mathrm{H}}_{2}\mathrm{O}$, ${\mathrm{C}\mathrm{u}}_{2}({\mathrm{C}}_{5}{\mathrm{H}}_{12}{\mathrm{N}}_{2}{)}_{2}{\mathrm{C}\mathrm{l}}_{4}$, etc.

arXiv:cond-mat/0309244Physical Review LettersNov 19, 200325 citations

A generalized spin ladder in a magnetic field

H. Frahm, C. Rödenbeck

arXiv:cond-mat/9812103The European Physical Journal BAug 1, 199918 citations

Spinless Fermionic ladders in a magnetic field

Sam T. Carr, B. N. Narozhny, A. A. Nersesyan

Bulletin of the American Physical SocietyMar 13, 20062 citations

We investigate the thermal and magnetic properties of the integrable

su(4)

ladder model by means of the quantum transfer matrix method. The magnetic susceptibility, specific heat, magnetic entropy, and high field magnetization are evaluated from the free energy derived via the recently proposed method of high temperature expansion for exactly solved models. We show that the integrable model can be used to describe the physics of the strong coupling ladder compounds. Excellent agreement is seen between the theoretical results and the experimental data for the known ladder compounds $(5\mathrm{I}\mathrm{A}\mathrm{P}{)}_{2}{\mathrm{C}\mathrm{u}\mathrm{B}\mathrm{r}}_{4}\ifmmode\cdot\else\textperiodcentered\fi{}2{\mathrm{H}}_{2}\mathrm{O}$,

{\mathrm{C}\mathrm{u}}_{2}({\mathrm{C}}_{5}{\mathrm{H}}_{12}{\mathrm{N}}_{2}{)}_{2}{\mathrm{C}\mathrm{l}}_{4}

, etc.