Rapid magnetic oscillations and magnetic breakdown in quasi-1D conductors

We review the physics of magnetic quantum oscillations in quasi-one dimensional conductors with an open Fermi surface, in the presence of modulated order. We emphasize the difference between situations where a modulation couples states on the same side of the Fermi surface and a modulation couples states on opposite sides of the Fermi surface. We also consider cases where several modulations coexist, which may lead to a complex reorganization of the Fermi surface. The interplay between nesting effects and magnetic breakdown is discussed. The experimental situation is reviewed.Comment: 10 pages, 8 figures, Contribution to the memorial issue in honor of J. Friedel, C. R. Acad. Sci. Pari

Towards a consistent picture for quasi-1D organic superconductors

The electrical resistivity of the quasi-1D organic superconductor (TMTSF)2PF6 was recently measured at low temperature from the critical pressure needed to suppress the spin-density-wave state up to a pressure where superconductivity has almost disappeared. This data revealed a direct correlation between the onset of superconductivity at Tc and the strength of a non-Fermi-liquid linear term in the normal-state resistivity, going as r(T) = r0 + AT + BT2 at low temperature, so that A goes to 0 as Tc goes to 0. Here we show that the contribution of low-frequency antiferromagnetic fluctuations to the spin-lattice relaxation rate is also correlated with this non-Fermi-liquid term AT in the resistivity. These correlations suggest that anomalous scattering and pairing have a common origin, both rooted in the low-frequency antiferromagnetic fluctuations measured by NMR. A similar situation may also prevail in the recently-discovered iron-pnictide superconductors.Comment: ISCOM'09 proceedings to be published in Physica

Study of the charge correlation function in one-dimensional Hubbard heterostructures

We study inhomogeneous one-dimensional Hubbard systems using the density matrix renormalization group method. Different heterostructures are investigated whose configuration is modeled varying parameters like the on-site Coulomb potential and introducing local confining potentials. We investigate their Luttinger liquid properties through the parameter K_rho, which characterizes the decay of the density-density correlation function at large distances. Our main goal is the investigation of possible realization of engineered materials and the ability to manipulate physical properties by choosing an appropriate spatial and/or chemical modulation.Comment: 6 pages, 7 figure

New possibility of the ground state of quarter-filled one-dimensional strongly correlated electronic system interacting with localized spins

We study numerically the ground state properties of the one-dimensional quarter-filled strongly correlated electronic system interacting antiferromagnetically with localized $S=1/2$ spins. It is shown that the charge-ordered state is significantly stabilized by the introduction of relatively small coupling with the localized spins. When the coupling becomes large the spin and charge degrees of freedom behave quite independently and the ferromagnetism is realized. Moreover, the coexistence of ferromagnetism with charge order is seen under strong electronic interaction. Our results suggest that such charge order can be easily controlled by the magnetic field, which possibly give rise to the giant negative magnetoresistance, and its relation to phthalocyanine compounds is discussed.Comment: 5pages, 4figure

Collective Spin-Density-Wave Response Perpendicular to the Chains of the Quasi One-Dimensional Conductor (TMTSF)2PF6

Microwave experiments along all three directions of the spin-density-wave model compound (TMTSF)$_2$PF$_6$ reveal that the pinned mode resonance is present along the $a$ and $b^{\prime}$ axes. The collective transport is considered to be the fingerprint of the condensate. In contrast to common quasi one-dimensional models, the density wave also slides in the perpendicular $b^{\prime}$ direction. The collective response is absent along the least conducting $c^*$ direction.Comment: 3 pages, 4 figure

Diamagnetism of doped two-leg ladders and probing the nature of their commensurate phases

We study the magnetic orbital effect of a doped two-leg ladder in the presence of a magnetic field component perpendicular to the ladder plane. Combining both low-energy approach (bosonization) and numerical simulations (density-matrix renormalization group) on the strong coupling limit (t-J model), a rich phase diagram is established as a function of hole doping and magnetic flux. Above a critical flux, the spin gap is destroyed and a Luttinger liquid phase is stabilized. Above a second critical flux, a reentrance of the spin gap at high magnetic flux is found. Interestingly, the phase transitions are associated with a change of sign of the orbital susceptibility. Focusing on the small magnetic field regime, the spin-gapped superconducting phase is robust but immediately acquires algebraic transverse (i.e. along rungs) current correlations which are commensurate with the 4k_F density correlations. In addition, we have computed the zero-field orbital susceptibility for a large range of doping and interactions ratio J/t : we found strong anomalies at low J/t only in the vicinity of the commensurate fillings corresponding to delta = 1/4 and 1/2. Furthermore, the behavior of the orbital susceptibility reveals that the nature of these insulating phases is different: while for delta = 1/4 a 4k_F charge density wave is confirmed, the delta = 1/2 phase is shown to be a bond order wave.Comment: 15 pages, 17 figure

SO(4) Theory of Competition between Triplet Superconductivity and Antiferromagnetism in Bechgaard Salts

Motivated by recent experiments with Bechgaard salts, we investigate the competition between antiferromagnetism and triplet superconductivity in quasi one-dimensional electron systems. We unify the two orders in an SO(4) symmetric framework, and demonstrate the existence of such symmetry in one-dimensional Luttinger liquids. SO(4) symmetry, which strongly constrains the phase diagram, can explain coexistence regions between antiferromagnetic, superconducting, and normal phases, as observed in (TMTSF)$_2$PF$_6$. We predict a sharp neutron scattering resonance in superconducting samples.Comment: 5 pages, 3 figures; Added discussion of applicability of SO(4) symmetry for strongly anisotropic Fermi liquids; Added reference