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1.
C. Honerkamp M. Salmhofer T.M. Rice 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):127-134
We extend the analysis of the renormalization group flow in the two-dimensional Hubbard model close to half-filling using
the recently developed temperature flow formalism. We investigate the interplay of d-density wave and Fermi surface deformation tendencies with those towards d-wave pairing and antiferromagnetism. For a ratio of next nearest to nearest neighbor hoppings, t'/t = - 0.25, and band fillings where the Fermi surface is inside the Umklapp surface, only the d-pairing susceptibility diverges at low temperatures. When the Fermi surface intersects the Umklapp surface close to the saddle
points, d-wave pairing, d-density wave, antiferromagnetic and, to a weaker extent, d-wave Fermi surface deformation susceptibilities grow together when the interactions flow to strong coupling. We interpret
these findings as indications for a non-trivial strongly coupled phase with short-ranged superconducting and antiferromagnetic
correlations, in close analogy with the spin liquid ground state in the well-understood two-leg Hubbard ladder.
Received 23 January 2002 相似文献
2.
Z.Á. Németh J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):87-101
In this second paper, using N = 3 polarized electrons (spinless fermions) interacting via a U/r Coulomb repulsion on a two dimensional L×L square lattice with periodic boundary conditions and nearest neighbor hopping t, we show that a single unpaired fermion can co-exist with a correlated two particle Wigner molecule for intermediate values
of the Coulomb energy to kinetic energy ratio r
s = UL/(2t
). This supports in an ultimate mesoscopic limit a possibility proposed by Andreev and Lifshitz for the thermodynamic limit:
a quantum crystal may have delocalized defects without melting, the number of sites of the crystalline array being smaller
than the total number of particles. When L = 6, the ground state exhibits four regimes as rs increases: a Hartree-Fock regime, a first supersolid regime where a correlated pair co-exists with a third fully delocalized
particle, a second supersolid regime where the third particle is partly delocalized, and eventually a correlated lattice regime.
Received 22 October 2002 Published online 23 May 2003
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ID="a"e-mail: jpichard@cea.fr 相似文献
3.
V. Hankevych F. Wegner 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):333-342
We present a stability analysis of the 2D t
-
t' Hubbard model on a square lattice for various values of the next-nearest-neighbor hopping t' and electron concentration. Using the free energy expression, derived by means of the flow equations method, we have performed
numerical calculation for the various representations under the point group C
4ν
in order to determine at which temperature symmetry broken phases become more favorable than the symmetric phase. A surprisingly
large number of phases has been observed. Some of them have an order parameter with many nodes in -space. Commonly discussed types of order found by us are antiferromagnetism, d
x2 - y2
-wave singlet superconductivity, d-wave Pomeranchuk instability and flux phase. A few instabilities newly observed are a triplet analog of the flux phase, a
particle-hole instability of p-type symmetry in the triplet channel which gives rise to a phase of magnetic currents, an s*-magnetic phase, a g-wave Pomeranchuk instability and the band splitting phase with p-wave character. Other weaker instabilities are found also. A comparison with experiments is made.
Received 25 July 2002 / Received in final form 28 November 2002 Published online 14 February 2003
RID="a"
ID="a"Current address: Département de physique and Centre de recherche sur les propriétés électroniques de matériaux avancés, Université de Sherbrooke,
Sherbrooke, Québec, Canada J1K 2R1 e-mail: vaha@physique.usherb.ca 相似文献
4.
We consider the competition between the one dimensionalization effect due to a magnetic field and the hopping parameters in quasi-one-dimensional conductors. Our study is based on a perturbative renormalization group method with three cut-off parameters, the bandwidth E0, the 1D-2D crossover temperature T*1, which is related to the hopping process t1, and the magnetic energy
. We have found that the renormalized crossover temperatures T*1 and T*2, at which the respectively hopping processes t1 and t2 become coherent, are reduced compared to the bare values as the field is increased. We discuss the consequences of these renormalization effects on the temperature-field phase diagram of the organic conductors.Received: 5 March 2003, Published online: 23 July 2003PACS:
64.60.-i General studies of phase transitions -
75.30.Fv Spin-density waves -
72.15.Gd Galvanomagnetic and other magnetotransport effects -
74.70.Kn Organic superconductors 相似文献
5.
D. Loison 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):517-521
We study the phase transition in generalized chiral or Stiefel's models using Monte Carlo simulations. These models are characterized
by a breakdown of symmetry O(N)/O(N-P). We show that the phase transition is clearly first order for when P=N and P=N-1, contrary to predictions based on the renormalization group in expansion but in agreement with a recent non perturbative renormalization group approach.
Received 7 October 1999 相似文献
6.
J.M. Drouffe C. Godrèche 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):281-288
We study the statistical properties of the sum S
t =
dt'σ
t', that is the difference of time spent positive or negative by the spin σ
t, located at a given site of a D-dimensional Ising model evolving under Glauber dynamics from a random initial configuration. We investigate the distribution
of St and the first-passage statistics (persistence) of this quantity. We discuss successively the three regimes of high temperature
( T > T
c), criticality ( T = T
c), and low temperature ( T < T
c). We discuss in particular the question of the temperature dependence of the persistence exponent , as well as that of the spectrum of exponents (x), in the low temperature phase. The probability that the temporal mean S
t/t was always larger than the equilibrium magnetization is found to decay as t
-
- ?. This yields a numerical determination of the persistence exponent in the whole low temperature phase, in two dimensions, and above the roughening transition, in the low-temperature phase
of the three-dimensional Ising model.
Received 4 December 2000 相似文献
7.
W. Hofstetter W. Zwerger 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):751-756
We present a field-theoretic renormalization group calculation in two loop order for classical O(N)-models with an inverse square interaction in the vicinity of their lower critical dimensionality one. The magnetic susceptibility
at low temperatures is shown to diverge like with a=(N-2)/(N-1) and . From a comparison with the exactly solvable Haldane-Shastry model we find that the same temperature dependence applies also
to ferromagnetic quantum spin chains.
Received: 20 February 1998 / Revised: 27 April 1998 / Accepted: 30 April 1998 相似文献
8.
Qingshan Yuan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):281-288
In this paper we study Peierls instabilities for a half-filled two-dimensional tight-binding model with nearest-neighbour
hopping t and next nearest-neighbour hopping t' at zero and finite temperatures. Two dimerization patterns corresponding to the same phonon vector (π,π) are considered to
be realizations of Peierls states. The effect of imperfect nesting introduced by t' on the Peierls instability, the properties of the dimerized ground state, as well as the competition between two dimerized
states for each t' and temperature T, are investigated. It is found: (i). The Peierls instability will be frustrated by t' for each of the dimerized states. The Peierls transition itself, as well as its suppression by t', may be of second- or first-order. (ii). When the two dimerized states are considered jointly, one of them will dominate
the other depending on parameters t' and T. Two successive Peierls transitions, that is, the system passing from the uniform state to one dimerized state and then to
the other may take place with decrease of temperature. Implications of our results to real materials are discussed.
Received 31 July 2001 相似文献
9.
M.-B. Lepetit M. Cousy G.M. Pastor 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):421-427
The half-filled Hubbard model on the Bethe lattice with coordination number z=3 is studied using the density-matrix renormalization group (DMRG) method. Ground-state properties such as the energy per
site E, average local magnetization , its fluctuations and various spin correlation functions are determined as a function of the Coulomb interaction strength U/t. The local magnetic moments increase monotonically with increasing Coulomb repulsion U/t showing antiferromagnetic order between nearest neighbors []. At large U/t, is strongly reduced with respect to the saturation value 1/2 due to exchange fluctuations between nearest neighbors (NN)
spins [ for ]. shows a maximum for U/t=2.4-2.9 that results from the interplay between the usual increase of with increasing U/t and the formation of important permanent moments at large U/t. While NN sites show antiferromagnetic spin correlations that increase with increasing Coulomb repulsion, the next NN sites
are very weakly correlated over the whole range of U/t. The DMRG results are discussed and compared with tight-binding calculations for U=0, independent DMRG studies for the Heisenberg model and simple first-order perturbation estimates.
Received 8 February 1999 and Received in final form 14 June 1999 相似文献
10.
Determination of equilibrium composition of C
x
H
y
O
z
N
t
plasmas out of thermodynamic equilibrium
Z. Koalaga 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):235-247
In this paper, we determine the composition of CxHyOzNt plasmas out of thermodynamic equilibrium using a more rigorous thermodynamic derivation of the Saha equation modified to
two-temperature plasma system proposed by Chen et al. The calculation is made for these plasmas in pressure range 0.1-1 MPa and for electron temperature range 5 000-30 000 K.
A great attention is given to the evolution of the major species such as hydrogen components (H, H2), carbon monoxide (CO) and electrons. We compared the results obtained with our previous experimental and theoretical studies;
the latter one has been carried out in equilibrium situation. We also compared our results with those given by the method
based on the minimization of the Gibbs free energy widely used in the literature.
Received 29 December 2000 and Received in final form 28 August 2001 相似文献
11.
12.
F. Selva J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):441-449
We study the difference between on site Hubbard and long range Coulomb repulsions for two interacting particles in a disordered
chain. The system size L (in units of the lattice spacing) is of the order of the one particle localization length and the energies are taken near
the band center. In the two cases, the limits of weak and strong interactions are characterized by uncorrelated energy levels
and are separated by a crossover regime where the states are more extended and the spectra more rigid. U denoting the interaction strength and t the kinetic energy scale, the crossovers take place for interaction energy to kinetic energy ratios U/t and U/(2tL) of order one, for Hubbard and Coulomb repulsions respectively. While Hubbard repulsion can only yield weak critical chaos
with intermediate spectral statistics, Coulomb repulsion can drive the two particle system to quantum chaos with Wigner-Dyson
spectral statistics. The interaction matrix elements are studied to explain this difference.
Received 21 March 2000 and Received in final form 5 February 2001 相似文献
13.
We discuss the occurrence and the stability of charge density plateaux in ladder-like t-J systems (at zero magnetization M = 0) for the cases of 2- and 3-leg ladders. Starting from isolated rungs at zero leg coupling, we study the behaviour of plateaux-related phase transitions by means of first order perturbation theory and compare our results with Lanczos diagonalizations for t-J ladders (N = 2 × 8) with increasing leg couplings. Furthermore we discuss the regimes of rung and leg couplings that should be favoured for the appearance of the charge density plateaux.Received: 28 July 2003, Published online: 8 December 2003PACS:
71.10.Fd Lattice fermion models (Hubbard model, etc.) - 71.27. + a Strongly correlated electron systems; heavy fermions - 75.10.-b General theory and models of magnetic ordering - 75.10.Jm Quantized spin models 相似文献
14.
H.W. Diehl M. Smock 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):567-587
A class of continuum models with a critical end point is considered whose Hamiltonian [φ,ψ] involves two densities: a primary order-parameter field, φ, and a secondary (noncritical) one, ψ. Field-theoretic methods
(renormalization group results in conjunction with functional methods) are used to give a systematic derivation of singularities
occurring at critical end points. Specifically, the thermal singularity ∼ | t|2 - α of the first-order line on which the disordered or ordered phase coexists with the noncritical spectator phase, and the coexistence
singularity ∼ | t|1 - α or ∼ | t|β of the secondary density <ψ> are derived. It is clarified how the renormalization group (RG) scenario found in position-space
RG calculations, in which the critical end point and the critical line are mapped onto two separate fixed points
CEP
* and
λ
*, translates into field theory. The critical RG eigenexponents of
CEP
* and
λ
* are shown to match.
CEP
* is demonstrated to have a discontinuity eigenperturbation (with eigenvalue y = d), tangent to the unstable trajectory that emanates from
CEP
* and leads to
λ
*. The nature and origin of this eigenperturbation as well as the role redundant operators play are elucidated. The results
validate that the critical behavior at the end point is the same as on the critical line.
Received 18 January 2001 相似文献
15.
D. Blume Chris H. Greene 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):83-86
We analyze various microscopic calculations of vibrational frequencies for 4HeN clusters, N = 3-728. The lowest breathing frequency with total angular momentum J = 0 varies smoothly as a function of N, with a maximum around N = 50-120.
Received 11 July 2001 相似文献
16.
Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves
a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition
for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization
(one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent
state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution.
Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M
* (M* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find
that: 1) for M
* ≪ M ≪ M
*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t1, t2, t3 and t*; 2) there are transient regimes (t
1 ≲ t ≲ t
3) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter
than t2. The chain growth is auto-accelerated for t
1 ≲ t ≲ t
2 : the cut-off chain length (= polymerization degree 〈n〉w
N
1 ∝ t
2 in this regime. 4) For t
2 < t < t
3 the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N1 is decreasing with time in this regime, while the length scale N2 of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t*, shows a sharp maximum in the vicinity of M*; the effective exponent
is as high as ∼ σ-1/3 just above M*. 相似文献
17.
We compute the dynamical structure factor S(q,τ) of an elastic medium where force dipoles appear at random in space and in time, due to “micro-collapses” of the structure.
Various regimes are found, depending on the wave vector q and the collapse time θ. In an early-time regime, the logarithm of the structure factor behaves as (qτ)3/2, as predicted in L. Cipelletti, S. Manley, R.C. Ball, D.A. Weitz, Phys. Rev. Lett. 84, 2275 (2000) using heuristic arguments. However, in an intermediate-time regime we rather obtain a (qτ)5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q
3/2τ. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation
time is found to grow with the age t
w, quasi-exponentially at first, and then as t
w
4/5 with logarithmic corrections.
Received 23 July 2001 相似文献
18.
We compute the dynamical structure factor S(q,τ) of an elastic medium where force dipoles appear at random in space and in time, due to “micro-collapses” of the structure.
Various regimes are found, depending on the wave vector q and the collapse time θ. In an early time regime, the logarithm of the structure factor behaves as (qτ)3/2, as predicted in (L. Cipelletti et al., Phys. Rev Lett. 84, 2275 (2000)) using heuristic arguments. However, in an intermediate-time regime we rather obtain a (qτ)5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q
3/2τ. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation
time is found to grow with the age tw, quasi-exponentially at first, and then as t
w
4/5 with logarithmic corrections.
Received 15 April 2002 相似文献
19.
M. Tsuchiizu P. Donohue Y. Suzumura T. Giamarchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):185-193
We investigate the physical properties of two coupled chains of electrons, with a nearly half-filled band, as a function of
the interchain hopping t
⊥ and the doping. We show that upon doping, the system undergoes a metal-insulator transition well described by a commensurate-incommensurate
transition. By using bosonization and renormalization we determine the full phase diagram of the system, and the physical
quantities such as the charge gap. In the commensurate phase two different regions, for which the interchain hopping is relevant
and irrelevant exist, leading to a confinement-deconfinement crossover in this phase. A minimum of the charge gap is observed
for values of t
⊥ close to this crossover. At large t
⊥ the region of the commensurate phase is enhanced, compared to a single chain. At the metal-insulator transition the Luttinger
parameter takes the universal value K
ρ
* = 1, in agreement with previous results on special limits of this model.
Received 31 July 2000 相似文献
20.
G. Katomeris F. Selva J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):401-412
In 1969, Andreev and Lifshitz have conjectured the existence of a supersolid phase taking place at zero temperature between
the quantum liquid and the solid. In this and a succeeding paper, we re-visit this issue for a few polarized electrons (spinless
fermions) interacting via a U/r Coulomb repulsion on a two dimensional L×L square lattice with periodic boundary conditions and nearest neighbor hopping t. This paper is restricted to the magic number of particles N = 4 for which a square Wigner molecule is formed when U increases and to the size L = 6 suitable for exact numerical diagonalizations. When the Coulomb energy to kinetic energy ratio r
s = UL/(2t
) reaches a value r
s
F ≈ 10, there is a level crossing between ground states of different momenta. Above r
s
F, the mesoscopic crystallization proceeds through an intermediate regime ( r
s
F < r
s < r
s
W ≈ 28) where unpaired fermions with a reduced Fermi energy co-exist with a strongly paired, nearly solid assembly. We suggest
that this is the mesoscopic trace of the supersolid proposed by Andreev and Lifshitz. When a random substrate is included,
the level crossing at r
s
F is avoided and gives rise to a lower threshold r
s
F(W) < r
s
F where two usual approximations break down: the Wigner surmise for the distribution of the first energy excitation and the
Hartree-Fock approximation for the ground state.
Received 21 June 2002 Published online 14 February 2003
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ID="a"e-mail: jpichard@cea.fr 相似文献