The Doped Two Chain Hubbard Model

The properties of the two-chain Hubbard Model doped away from half-filling are investigated. The charge gap is found to vanish, but a finite spin gap exists over a range of interchain hopping strength $t_\perp$. In this range, there are modified $d_{x^2-y^2}$--like pairing correlations whose strength is correlated with the size of the spin gap. It is found that the pair field correlations are enhanced by the onsite Coulomb interaction U.Comment: 10 pages and 5 postscript figures, RevTeX 3.0, UCI-CMTHE-94-0

On the dimerized phase in the cross-coupled antiferromagnetic spin ladder

We revisit the phase diagram of the frustrated s=1/2 spin ladder with antiferromagnetic rung and diagonal couplings. In particular, we reexamine the evidence for the columnar dimer phase, which has been predicted from analytic treatment of the model and has been claimed to be found in numerical calculations. By considering longer chains and by keeping more states than in previous work using the density-matrix renormalization group, we show that the numerical evidence presented previously for the existence of the dimerized phase is not unambiguous in view of the present more careful analysis. While we cannot completely rule out the possibility of a dimerized phase in the cross-coupled ladder, we do set limits on the maximum possible value of the dimer order parameter that are much smaller than those found previously.Comment: 6 pages, 7 figure

Studying a relativistic field theory at finite chemical potential with the density matrix renormalization group

The density matrix renormalization group is applied to a relativistic complex scalar field at finite chemical potential. The two-point function and various bulk quantities are studied. It is seen that bulk quantities do not change with the chemical potential until it is larger than the minimum excitation energy. The technical limitations of the density matrix renormalization group for treating bosons in relativistic field theories are discussed. Applications to other relativistic models and to nontopological solitons are also suggested.Comment: 9 pages, 5 figures; v2: title changed; references added, conclusions expanded, to be published in PR

The Distribution of CAP Payments - Redistributional Injustice or Spatially Adapted policy?

This paper analyses the distributional equality of individual Scottish Government-administered payments in 2008 under CAP Pillars One (single farm payments) and Two (rural development measures) and in total, in terms of economic, social and spatial factors. The analysis shows that 94% of all payments were paid to claimants in core rural areas (94%) while only a few (5%) claimants resided in urban areas or outside of Scotland (1%). However, in both Pillars, claims made by urban residents were often higher than those made by rural dwellers. The Ordinary Least Squares spatial analysis shows that the level of payments was extremely dependent on the geographical location and natural conditions. Spatial factors describing the economic situation in the area of the claimant were significantly related to the level of the CAP amounts paid. Overall, the level of amounts paid was positively related to the natural, economic and social structures of the area of residence. The discussion tackles the question of whether the current system of farm income support by decoupled payments should be developed into a poverty payment system.Pillar One, Common Agricultural Policy, Gini-Coefficient, Rural-Urban distribution, distributional justice, Land Economics/Use, Q15, R14, R11,

Uniform and staggered magnetizations induced by Dzyaloshinskii-Moriya interactions in isolated and coupled spin 1/2 dimers in a magnetic field

We investigate the interplay of Dzyaloshinskii-Moriya interactions and an external field in spin 1/2 dimers. For isolated dimers and at low field, we derive simple expressions for the staggered and uniform magnetizations which show that the orientation of the uniform magnetization can deviate significantly from that of the external field. In fact, in the limit where the ${\bf D}$ vector of the Dzyaloshinskii-Moriya interaction is parallel to the external field, the uniform magnetization actually becomes {\it perpendicular} to the field. For larger fields, we show that the staggered magnetization of an isolated dimer has a maximum close to one-half the polarization, with a large maximal value of $0.35 g\mu_B$ in the limit of very small Dzyaloshinskii-Moriya interaction. We investigate the effect of inter-dimer coupling in the context of ladders with Density Matrix Renormalization Group (DMRG) calculations and show that, as long as the values of the Dzyaloshinskii-Moriya and of the exchange interaction are compatible with respect to the development of a staggered magnetization, the simple picture that emerges for isolated dimers is also valid for weakly coupled dimers with minor modifications. The results are compared with torque measurements on Cu$_{2}$(C$_{5}$H$_{12}$N$_{2}$)$_{2}$Cl$_{4}$.Comment: 8 pages, 9 figure