arXiv subjects

E. Orignac

Publications and source records attributed to E. Orignac.

58 records · Page 4Linked to original sources

arXiv1998

Vortices in coupled planes with columnar disorder and bosonic ladders

We consider two coupled strongly correlated bosonic chains. We derive the phase diagram of the pure system and obtain an antisymmetric charge density wave, a 4k_F charge density wave, a superfluid phase and a second superfluid phase which is a condensate of boson pairs. We consider the effect of a weak disorder on that system and show that the superfluid phase is less localized than in the one chain case. On the other hand, the pinning length of the antisymmetric charge density wave is shorter than in the one chain case. We discuss the consequences of these results for two coupled vortex planes with columnar disorder. We show that in the vortex system there is a conventional pinned solid phase for 0 T_L. We obtain the critical currents by a modified Larkin-Ovchinnikov argument and prove that there is a strong reduction of critical current for T=T_m.

cond-mat.str-el↗

arXiv1997

Weakly disordered spin ladders

We analyze an anisotropic spin 1/2 two legs ladder in the presence of various type of random perturbations. The generic phase diagram for the pure system, in a way similar to spin one chains, consists of four phases: an Antiferromagnet, a Haldane gap or a Singlet phase (depending on the sign of interchain coupling) and two XY phases designated by XY1 and XY2. The effects of disorder depend crucially on whether it preserves XY symmetry (random field along z and random exchange) or not (random anisotropy or random XY fields). The singlet phases and the massless XY1 phase are totally unaffected by disorder in stark contrast with the single chain case. On the other hand the XY2 phase is very strongly suppressed. Disorder breaking XY symmetry has much stronger effects and most of the phases at the exception of the singlet one are destroyed. Interestingly, the disordered XY1 phase has a much shorter correlation length than the disordered XY2 phase contrarily with the case of perturbations preserving the rotation symmetry around the z axis.

cond-mat.str-el↗

arXiv1997

Effects of disorder on two strongly correlated coupled chains

We study the effects of disorder on a system of two coupled chain of strongly correlated fermions (ladder system), using renormalization group. The stability of the phases of the pure system is investigated as a function of interactions both for fermions with spin and spinless fermions. For spinless fermions the repulsive side is strongly localized whereas the system with attractive interactions is stable with respect to disorder, at variance with the single chain case. For fermions with spins, the repulsive side is also localized, and in particular the d-wave superconducting phase found for the pure system is totally destroyed by an arbitrarily small amount of disorder. On the other hand the attractive side is again remarkably stable with respect to localization. We have also computed the charge stiffness, the localization length and the temperature dependence of the conductivity for the various phases. In the range of parameter where d-wave superconductivity would occur for the pure system the conductivity is found to decrease monotonically with temperature, even at high temperature, and we discuss this surprising result. For a model with one site repulsion and nearest neighbor attraction, the most stable phase is an orbital antiferromagnet . Although this phase has no divergent superconducting fluctuation it can have a divergent conductivity at low temperature. We argue based on our results that the superconductivity observed in some two chain compounds cannot be a simple stabilization of the d-wave phase found for a pure single ladder. Applications to quantum wires are discussed.

cond-mat.str-el↗

arXiv1995

Effects of a weak disorder on two coupled Hubbard chains

We consider the effect of weak nonmagnetic disorder on two chains of interacting fermions (with and without spins) coupled by interchain hopping. For the spinless case, interchain hopping increases localization for repulsive interactions but {\it stabilizes} the s-wave superconducting phase for attractive interactions. For the case with spin, the d-wave phase arising from purely repulsive interactions in the clean system is destroyed by an infinitesimal disorder while for attractive interactions, the s-wave superconductivity is more resistant to disorder than in the one-chain case.

cond-mat↗