Ground-state phase diagram of a half-filled one-dimensional extended Hubbard model

The density-matrix renormalization group is used to study the phase diagram of the one-dimensional half-filled Hubbard model with on-site (U) and nearest-neighbor (V) repulsion, and hopping t. A critical line V_c(U) approximately equal to U/2 separates a Mott insulating phase from a charge-density-wave phase. The formation of bound charge excitations for V > 2t changes the phase transition from continuous to first order at a tricritical point U_t = 3.7t, V_t=2t. A frustrating effective antiferromagnetic spin coupling induces a bond-order-wave phase on the critical line V_c(U) for U_t < U < 7-8 t.Comment: 4 pages (REVTEX 4), 3 EPS figures, shorter abstract, text and references modifie

Superconducting pairing and density-wave instabilities in quasi-one-dimensional conductors

Using a renormalization group approach, we determine the phase diagram of an extended quasi-one-dimensional electron gas model that includes interchain hopping, nesting deviations and both intrachain and interchain repulsive interactions. d-wave superconductivity, which dominates over the spin-density-wave (SDW) phase at large nesting deviations, becomes unstable to the benefit of a triplet $f$-wave phase for a weak repulsive interchain backscattering term $g_1^\perp>0$, despite the persistence of dominant SDW correlations in the normal state. Antiferromagnetism becomes unstable against the formation of a charge-density-wave state when $g_1^\perp$ exceeds some critical value. While these features persist when both Umklapp processes and interchain forward scattering ($g_2^\perp$) are taken into account, the effect of $g_2^\perp$ alone is found to frustrate nearest-neighbor interchain $d$- and $f$-wave pairing and instead favor next-nearest-neighbor interchain singlet or triplet pairing. We argue that the close proximity of SDW and charge-density-wave phases, singlet d-wave and triplet $f$-wave superconducting phases in the theoretical phase diagram provides a possible explanation for recent puzzling experimental findings in the Bechgaard salts, including the coexistence of SDW and charge-density-wave phases and the possibility of a triplet pairing in the superconducting phase.Comment: 19 pages, 13 figure

Influence of carrier lifetime on quantum criticality and superconducting Tc of (TMTSF)_2ClO_4

This work presents and analyzes electrical resistivity data on the organic superconductor (TMTSF)$_2$ClO$_4$ and their anion substituted alloys (TMTSF)$_2$(ClO$_4$)$_{1-x}$(ReO$_4$)$_x$ along the least conducting $c^\star$ axis. Nonmagnetic disorder introduced by finite size domains of anion ordering on non Fermi liquid character of resistivity is investigated near the conditions of quantum criticality. The evolution of the $T$-linear resistivity term with anion disorder shows a limited decrease in contrast with the complete suppression of the critical temperature $T_c$ as expected for unconventional superconductivity beyond a threshold value of $x$. The resulting breakdown of scaling between both quantities is compared to the theoretical predictions of a linearized Boltzmann equation combined to the scaling theory of umklapp scattering in the presence of disorder induced pair-breaking for the carriers.Comment: 13 pages, 8 figure

Renormalization Group calculations with k|| dependent couplings in a ladder

We calculate the phase diagram of a ladder system, with a Hubbard interaction and an interchain coupling $t_\perp$. We use a Renormalization Group method, in a one loop expansion, introducing an original method to include $k_{||}$ dependence of couplings. We also classify the order parameters corresponding to ladder instabilities. We obtain different results, depending on whether we include $k_{||}$ dependence or not. When we do so, we observe a region with large antiferromagnetic fluctuations, in the vicinity of small $t_\perp$, followed by a superconducting region with a simultaneous divergence of the Spin Density Waves channel. We also investigate the effect of a non local backward interchain scattering : we observe, on one hand, the suppression of singlet superconductivity and of Spin Density Waves, and, on the other hand, the increase of Charge Density Waves and, for some values of $t_\perp$, of triplet superconductivity. Our results eventually show that $k_{||}$ is an influential variable in the Renormalization Group flow, for this kind of systems.Comment: 20 pages, 19 figures, accepted in Phys. Rev. B 71 v. 2

CDW Ordering in Stripe Phase of Underdoped Cuprates

The in-plane resistivity and out-of-plane resistivity of non-superconducting RBCO (R = Y, Tm) and Fe-doped Bi2212 single crystals are discussed. The comparison of electrical transport properties of the cuprates and quasi-one dimensional (1D) (TMTSF)2PF6 organic conductor suggests that RBCO and Bi2212 exhibit 1D transport properties, and the step rise at low temperatures in the resistivities of the cuprates and quasi-1D organic conductor is due to charge-density-wave ordering. We discuss also phonon-electron interactions in cuprates at low temperatures.Comment: 10 pages including 4 figure

A Renormalization group approach for highly anisotropic 2D Fermion systems: application to coupled Hubbard chains

I apply a two-step density-matrix renormalization group method to the anisotropic two-dimensional Hubbard model. As a prelude to this study, I compare the numerical results to the exact one for the tight-binding model. I find a ground-state energy which agrees with the exact value up to four digits for systems as large as $24 \times 25$. I then apply the method to the interacting case. I find that for strong Hubbard interaction, the ground-state is dominated by magnetic correlations. These correlations are robust even in the presence of strong frustration. Interchain pair tunneling is negligible in the singlet and triplet channels and it is not enhanced by frustration. For weak Hubbard couplings, interchain non-local singlet pair tunneling is enhanced and magnetic correlations are strongly reduced. This suggests a possible superconductive ground state.Comment: 8 pages, 11 figures, expanded version of cond-mat/060856

Triplet superconducting pairing and density-wave instabilities in organic conductors

Using a renormalization group approach, we determine the phase diagram of an extended quasi-one-dimensional electron gas model that includes interchain hopping, nesting deviations and both intrachain and interchain repulsive interactions. We find a close proximity of spin-density- and charge-density-wave phases, singlet d-wave and triplet f-wave superconducting phases. There is a striking correspondence between our results and recent puzzling experimental findings in the Bechgaard salts, including the coexistence of spin-density-wave and charge-density-wave phases and the possibility of a triplet pairing in the superconducting phase.Comment: 4 pages, 5 eps figure