Finite-size effects in Luther-Emery phases of Holstein and Hubbard models

The one-dimensional Holstein model and its generalizations have been studied extensively to understand the effects of electron-phonon interaction. The half-filled case is of particular interest, as it describes a transition from a metallic phase with a spin gap due to attractive backscattering to a Peierls insulator with charge-density-wave (CDW) order. Our quantum Monte Carlo results support the existence of a metallic phase with dominant power-law charge correlations, as described by the Luther-Emery fixed point. We demonstrate that for Holstein and also for purely fermionic models the spin gap significantly complicates finite-size numerical studies, and explains inconsistent previous results for Luttinger parameters and phase boundaries. On the other hand, no such complications arise in spinless models. The correct low-energy theory of the spinful Holstein model is argued to be that of singlet bipolarons with a repulsive, mutual interaction. This picture naturally explains the existence of a metallic phase, but also implies that gapless Luttinger liquid theory is not applicable.Comment: 17 pages, 18 figures, final versio

Hilfsmittel in der Rheumatologie

Due to the frequent presence of comorbidities in patients suffering from rheumatism with increased perioperative risk factors, conservative treatment is often needed. Besides pharmacological treatment, physiotherapy and occupational therapy, a variety of orthoses are available depending on the individual indications. They can be used to stabilize or support joints, limit the range of motion, prevent unphysiological movements or provide relief for affected limbs. In order to choose the right kind of orthosis, the physician should know the underlying cause of disease. Furthermore, for patients with rheumatism many devices are available for daily living that use ergonomic handles or improved leverage effects to compensate for the often severe limitations and to improve the quality of life