665 research outputs found
Two-loop renormalization-group theory for the quasi-one-dimensional Hubbard model at half filling
We derive two-loop renormalization-group equations for the half-filled
one-dimensional Hubbard chains coupled by the interchain hopping. Our
renormalization-group scheme for the quasi-one-dimensional electron system is a
natural extension of that for the purely one-dimensional systems in the sense
that transverse-momentum dependences are introduced in the g-ological coupling
constants and we regard the transverse momentum as a patch index. We develop
symmetry arguments for the particle-hole symmetric half-filled Hubbard model
and obtain constraints on the g-ological coupling constants by which resultant
renormalization equations are given in a compact form. By solving the
renormalization-group equations numerically, we estimate the magnitude of
excitation gaps and clarify that the charge gap is suppressed due to the
interchain hopping but is always finite even for the relevant interchain
hopping. To show the validity of the present analysis, we also apply this to
the two-leg ladder system. By utilizing the field-theoretical bosonization and
fermionization method, we derive low-energy effective theory and analyze the
magnitude of all the excitation gaps in detail. It is shown that the low-energy
excitations in the two-leg Hubbard ladder have SO(3) x SO(3) x U(1) symmetry
when the interchain hopping exceeds the magnitude of the charge gap.Comment: 18 pages, 9 figures; Two appendices and one figure adde
Superconductor-to-Spin-Density-Wave Transition in Quasi-One-Dimensional Metals with Ising Anisotropy
We study a mechanism for superconductivity in quasi-one-dimensional materials
with Ising anisotropy. In an isolated chain Ising anisotropy opens a spin gap;
if inter-chain coupling is sufficiently weak, single particle hopping is
suppressed and the physics of coupled chains is controlled by a competition
between pair hopping and exchange interaction. Spin density wave and triplet
superconductivity phases are found separated by a first order phase transition.
For particular parameter values a second order transition described by SO(4)
symmetry is found.Comment: 18 pages, 1 figur
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
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
N-loss stoichiometry in a Peru ODZ eddy
Assuming heterotrophic denitrification as the dominant microbial process, Richards (1965) formulated a stoichiometry governing nitrogen loss in open-ocean oxygen deficient zones (ODZs). It prescribes the quantitative coupling between the oxidation of organic matter by NO–3 in the absence of O2 and the corresponding production of CO2, N2, and PO–34. Applied globally, this relationship defines key linkages between the C, N, and P cycles. However, the validity of Richards\u27s stoichiometry is challenged by recognition of complex microbial N processing in ODZs including anammox as an important pathway and nitrite reoxidation. Whereas Richards\u27s stoichiometry would result in N2-N production to NO–3 removal rates of 1.17, dominance by anammox with respect to biogenic N2 production could in theory result in a ratio as high as 2. Ratios with PO–34 production provide an additional constraint on the quantity and composition of respired organic matter. Here we use a mesoscale eddy with extreme N-loss in the Peru ODZ as a natural laboratory to examine N-loss stoichiometry. Its intense biogeochemical signatures, relatively well-defined timescales, and simplified hydrography allowed for the development of strong co-occurring gradients in NO–3, NO–2, biogenic N2, and PO–34. The production of biogenic N2 as compared with the removal of NO–3 (analyzed either directly or as N deficits) was slightly less than predicted by Richards\u27s stoichiometry and did not at all support any excess biogenic N2. PO–34 production, however, was twice the expectation from Richards\u27s stoichiometry suggesting that respired organic matter was P-rich as compared with C:N:P Redfield composition. These results suggest major gaps remain between current understanding of microbial N pathways in ODZs and their net biogeochemical output
- …