Thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies

The thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies are investigated via the integrable su(3) model in terms of the quantum transfer matrix method and the recently developed high temperature expansion method for exactly solved models. It is shown that large single-ion anisotropy may result in a singlet gapped phase in the spin-1 chain which is significantly different from the standard Haldane phase. A large in-plane anisotropy may destroy the gapped phase. On the other hand, in the vicinity of the critical point a weak in-plane anisotropy leads to a different phase transition than the Pokrovsky-Talapov transition. The magnetic susceptibility, specific heat and magnetization evaluated from the free energy are in excellent agreement with the experimental data for the compounds NiC_2H_8N_2)_2Ni(CN)_4 and Ni(C_{10}H_8N_2)_2Ni(CN)_4.H_2O.Comment: 18 pages, 6 figures, to appear in PR

Emergent quantum phases in a heteronuclear molecular Bose--Einstein condensate model

We study a three-mode Hamiltonian modelling a heteronuclear molecular Bose--Einstein condensate. Two modes are associated with two distinguishable atomic constituents, which can combine to form a molecule represented by the third mode. Beginning with a semi-classical analogue of the model, we conduct an analysis to determine the phase space fixed points of the system. Bifurcations of the fixed points naturally separate the coupling parameter space into different regions. Two distinct scenarios are found, dependent on whether the imbalance between the number operators for the atomic modes is zero or non-zero. This result suggests the ground-state properties of the model exhibit an unusual sensitivity on the atomic imbalance. We then test this finding for the quantum mechanical model. Specifically we use Bethe ansatz methods, ground-state expectation values, the character of the quantum dynamics, and ground-state wavefunction overlaps to clarify the nature of the ground-state phases. The character of the transition is smoothed due to quantum fluctuations, but we may nonetheless identify the emergence of a quantum phase boundary in the limit of zero atomic imbalance.Comment: 23 pages, 10 figure

Exact results for the thermal and magnetic properties of strong coupling ladder compounds

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 (5IAP)$_2$CuBr$_4$$\cdot$2H$_2$O, Cu$_{2}$(C$_5$H$_{12}$N$_2$)$_2$Cl$_4$ etc.Comment: 10 pages, 5 figure

Ground-state properties of the attractive one-dimensional Bose-Hubbard model

We study the ground state of the attractive one-dimensional Bose-Hubbard model, and in particular the nature of the crossover between the weak interaction and strong interaction regimes for finite system sizes. Indicator properties like the gap between the ground and first excited energy levels, and the incremental ground-state wavefunction overlaps are used to locate different regimes. Using mean-field theory we predict that there are two distinct crossovers connected to spontaneous symmetry breaking of the ground state. The first crossover arises in an analysis valid for large L with finite N, where L is the number of lattice sites and N is the total particle number. An alternative approach valid for large N with finite L yields a second crossover. For small system sizes we numerically investigate the model and observe that there are signatures of both crossovers. We compare with exact results from Bethe ansatz methods in several limiting cases to explore the validity for these numerical and mean-field schemes. The results indicate that for finite attractive systems there are generically three ground-state phases of the model.Comment: 17 pages, 12 figures, Phys.Rev.B(accepted), minor changes and updated reference

Exact Results for the One-Dimensional Mixed Boson-Fermion Interacting Gas

The exact solution of the one-dimensional interacting mixed boson-fermion gas is used to calculate ground-state properties both for finite systems and in the thermodynamic limit. The quasimomentum distribution, ground-state energy, and generalized velocities are obtained as functions of the interaction strength both for polarized and nonpolarized fermions. We do not observe any demixing instability of the system for repulsive interactions

Thermal and Magnetic Properties of Integrable Spin-1 and Spin-3/2 Chains with Applications to Real Compounds

The ground state and thermodynamic properties of spin-1 and spin- 3/2 chains are investigated via exactly solved su(3) and su(4) models with physically motivated chemical potential terms. The analysis involves the thermodynamic Bethe ansatz and the high temperature expansion (HTE) methods. For the spin-1 chain with large single-ion anisotropy, a gapped phase occurs which is significantly different from the valence-bond-solid Haldane phase. The theoretical curves for the magnetization, susceptibility and specific heat are favourably compared with experimental data for a number of spin-1 chain compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at zero external magnetic field. A middle magnetization plateau can be triggered by the single-ion anisotropy term. Overall, our results lend further weight to the applicability of integrable models to the physics of low-dimensional quantum spin systems. They also highlight the utility of the exact HTE method

Exact Results for the 1D Interacting Fermi Gas with Arbitrary Polarization

We investigate the 1D interacting two-component Fermi gas with arbitrary polarization. Exact results for the ground state energy, quasimomentum distribution functions, spin velocity and charge velocity reveal subtle polarization dependent quantum effects

Advances in hormone replacement therapy with drospirenone, a unique progestogen with aldosterone receptor antagonism

Unlike other currently available progestogens, drospirenone (DRSP) has a pharmacological profile, which closely mimics that of endogenous progesterone, most notably potent anti-aldosterone and anti-androgenic effects. Consequently, DRSP, when combined with 17 beta-estradiol (E2) as hormone replacement therapy (HRT), offsets E2-related water and sodium retention by blocking the mineralocorticoid receptor. This review evaluates the potential benefits offered by DRSP as the progestin component of HRT with respect to its anti-aldosterone activity, which translates into positive effects on body weight and blood pressure in clinical trials of continuous, combined E2/DRSP in post-menopausal women. In a 1-year, large-scale, randomised, controlled trial, E2 1 mg/DRSP 2 mg significantly decreased mean body weight by 1.2 kg versus baseline (P = 5.5 meq/L) irrespective of concomitant use of ACE inhibitors, angiotensin II receptor antagonists or non-steroidal anti-inflammatory drugs, and co-morbid diabetes mellitus. In summary, as well as effectively treating climacteric symptoms, DRSP 2 mg combined with E2 I mg has shown positive effects on body weight and blood pressure in clinical trials, most likely due to DRSP's anti-aldosterone properties. This combination may therefore offer an alternative therapeutic option with additional benefits beyond current HRT agents for symptomatic post-menopausal women. (c) 2006 Elsevier Ireland Ltd. All rights reserved