494 research outputs found

### Angle-Resolved Loss of Landau Quasiparticles in 2D Hubbard Model

The problem of weakly correlated electrons on a square lattice is studied
theoretically. A simple renormalization group scheme for the angle-resolved
weight Z of the quasiparticles at the Fermi surface is presented and applied to
the Hubbard model.
Upon reduction of the cutoff the Fermi surface is progressively destroyed
from the van Hove points toward the zone diagonals. Due to the renormalized Z,
divergences of both antiferromagnetic and superconducting correlation functions
are suppressed at the critical scale, where the interactions diverge.Comment: 13 pages, 2 figures, submitted to Europhysics Letter

### Angle-resolved study of density-waves, superconductivity and pseudogap in two dimensions

Weakly correlated electrons on a square lattice are studied by angle-resolved
functional renormalization group. Upon renormalization the interaction starts
to depend on momenta and has pole-like solutions near a doping-dependent
characteristic critical energy scale. Near half-filling this scale is the
pseudogap temperature T*. In the overdoped regime the critical scale is the
mean-field like critical temperature for d-wave superconductivity.Comment: 4 pages, 2 figure

### New SDW phases in quasi-one-dimensional systems dimerized in the transverse direction

The spin density wave instabilities in the quasi-one-dimensional metal
(TMTSF)_2ClO_4 are studied in the framework a matrix random phase approximation
for intra-band and inter-band order parameters. Depending on the anion ordering
potential V which measures the lattice doubling in the transverse direction,
two different instabilities are possible. The SDW_0 state at low values of V is
antiferromagnetic in b direction and has the critical temperature that
decreases rapidly with V. The degenerated states SDW_(+-), stable at higher
values of V, are superpositions of two magnetic orders, each one on its
subfamily of chains. As V increases the ratio between two components of
SDW_(+-) tends to zero and the critical temperature increases asymptotically
towards that of SDW instability for a system having perfect nesting and no
anion order. At intermediate V the metallic state can persist down to T=0.Comment: Submitted to Europhysics Letter

### Magnetic oscillations and field induced spin density waves in (TMTSF)_2ClO_4

We report an analysis of the effects of magnetic field on a
quasi-one-dimensional band of interacting electrons with a transverse
dimerizing potential. One-particle problem in bond-antibond representation is
solved exactly. The resulting propagator is used to calculate the
spin-density-wave (SDW) response of the interacting system within the matrix
RPA for the SDW susceptibility. We predict the magnetic field induced
transition of the first order between interband SDW_0 and intraband SDW_(+-)
phases. We reproduce the rapid oscillations with a period of 260 Tesla and the
overal profile of the TMTSF_2ClO_4 phase diagram.Comment: 6 pages, 3 figure

### Colloidal stability of tannins: astringency, wine tasting and beyond

Tannin-tannin and tannin-protein interactions in water-ethanol solvent
mixtures are studied in the context of red wine tasting. While tannin
self-aggregation is relevant for visual aspect of wine tasting (limpidity and
related colloidal phenomena), tannin affinities for salivary proline-rich
proteins is fundamental for a wide spectrum of organoleptic properties related
to astringency. Tannin-tannin interactions are analyzed in water-ethanol
wine-like solvents and the precipitation map is constructed for a typical grape
tannin. The interaction between tannins and human salivary proline-rich
proteins (PRP) are investigated in the framework of the shell model for
micellization, known for describing tannin-induced aggregation of beta-casein.
Tannin-assisted micellization and compaction of proteins observed by SAXS are
described quantitatively and discussed in the case of astringency

### Pauli and orbital effects of magnetic field on charge density waves

Taking into account both Pauli and orbital effects of external magnetic field
we compute the mean field phase diagram for charge density waves in
quasi-one-dimensional electronic systems. The magnetic field can cause
transitions to CDW states with two types of the shifts of wave vector from its
zero-field value. It can also stabilize the field-induced charge density wave.
Furthermore, the critical temperature shows peaks at a new kind of magic
angles.Comment: 3 pages, 1 figure include

### U-J Synergy Effect for the High Tc Superconductors

Using renormalization group and exact diagonalization of small clusters we
investigate the ground state phase diagram of a two-dimensional extended
Hubbard model with nearest-neighbor exchange interaction J, in addition to the
local Coulomb repulsion U. The main instabilities are antiferromagnetism close
to half-filling and d-wave superconductivity in the doped system. Our results
suggest that the combined action of J and U interactions provide a remarkably
efficient mechanism to enhance both d-wave superconducting and
antiferromagnetic correlations.Comment: Final version, to appear in PR

### Weakly correlated electrons on a square lattice: a renormalization group theory

We study the weakly interacting Hubbard model on the square lattice using a
one-loop renormalization group approach. The transition temperature T_c between
the metallic and (nearly) ordered states is found. In the parquet regime, (T_c
>> |mu|), the dominant correlations at temperatures below T_c are
antiferromagnetic while in the BCS regime (T_c << |mu|) at T_c the d-wave
singlet pairing susceptibility is most divergent.Comment: 12 pages, REVTEX, 3 figures included, submitted to Phys. Rev. Let

### Pauli coupling of the external magnetic field to spin-density waves

The effects of the external magnetic field on the spin-density-wave (SDW) order and on accompanying fluctuations are calculated within the random-phase approximation for the extended Hubbard model with imperfectly nested quasi-one-dimenisonal Fermi surfaces. Both Pauli and orbital mechanisms are treated in parallel. It is shown that the Pauli coupling leads to a finite hybridization of the SDW component in the direction of the external field and the charge-density wave. The mean value of this SDW component remains zero below the critical temperature in the isotropic system, but may be activated in systems with an internal spin anisotropy. The mean-field expression for the corresponding spin-flop field is derived. Furthermore, the Pauli coupling renormalizes two of six fluctuative SDW modes. In order to establish ways of qualitative and quantitative comparison between effects belonging to the Pauli and orbital couplings, we analyze the characteristic parameters for these two modes as well as for the other four modes affected only by the orbital coupling. In particular we evaluate the field dependence of longwavelength gaps, correlation lengths, and attenuation coefficients

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