493 research outputs found
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 -wave phase for a weak repulsive interchain
backscattering term , despite the persistence of dominant SDW
correlations in the normal state. Antiferromagnetism becomes unstable against
the formation of a charge-density-wave state when exceeds some
critical value. While these features persist when both Umklapp processes and
interchain forward scattering () are taken into account, the effect
of alone is found to frustrate nearest-neighbor interchain - and
-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 -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)ClO and their anion substituted alloys
(TMTSF)(ClO)(ReO) along the least conducting
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 -linear resistivity
term with anion disorder shows a limited decrease in contrast with the complete
suppression of the critical temperature as expected for unconventional
superconductivity beyond a threshold value of . 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 . We use a Renormalization Group method, in
a one loop expansion, introducing an original method to include
dependence of couplings. We also classify the order parameters corresponding to
ladder instabilities. We obtain different results, depending on whether we
include dependence or not. When we do so, we observe a region with
large antiferromagnetic fluctuations, in the vicinity of small ,
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 , of triplet
superconductivity. Our results eventually show that 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 . 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
- …