共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
2.
T. Vuletić P. Auban-Senzier C. Pasquier S. Tomić D. Jérome M. Héritier K. Bechgaard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):319-331
The phase diagram of the organic superconductor (TMTSF)2PF6has been revisited using transport measurements with an improved control of the applied pressure. We have found a 0.8 kbar
wide pressure domain below the critical point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground state
featuring a coexistence regime between spin density wave (SDW) and superconductivity (SC). The inhomogeneous character of
the said pressure domain is supported by the analysis of the resistivity between T
SDW
and T
SC
and the superconducting critical current. The onset temperature T
SC
is practically constant ( 1.20±0.01 K) in this region where only the SC/SDW domain proportion below T
SC
is increasing under pressure. An homogeneous superconducting state is recovered above the critical pressure with T
SC
falling at increasing pressure. We propose a model comparing the free energy of a phase exhibiting a segregation between
SDW and SC domains and the free energy of homogeneous phases which explains fairly well our experimental findings.
Received 3 September 2001 and Received in final form 9 November 2001 相似文献
3.
Current-voltage (J-V) and differential-conductivity-voltage ( dJ/dV-V) characteristics are analytically calculated at zero temperature for a point contact consisting of: two Peierls conductors
P
( = 1, 2) separated by an insulator (I). Here P is a conductor with charge density wave (CDW). The J-V and dJ/dV-V characteristics depend on the CDW phases ( = 1, 2) in the mean field approximation. To calculate them analytically we assumed, = ≡Δ where ( = 1, 2) are the energy gaps of P
( = 1, 2). The current J has a discontinuous jump at eV = 2Δ for ϕ
1 = ϕ
2≠ 0. The differential conductivity dJ/dV has a singularity at eV = 2Δ for ϕ
1 = ϕ
2≠ 0. The relation J(V,ϕ
1,ϕ
2) = - J(- V,ϕ
1 + π,ϕ
2 + π) is obtained.
Received 4 July 2001 and Received in final form 13 September 2001 相似文献
4.
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
5.
I. Bâldea H. Köppel L.S. Cederbaum 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):289-299
We present a new effect that is possible for strongly correlated electrons in commensurate mesoscopic rings: the collective tunneling of electrons between classically equivalent configurations, corresponding to ordered states possessing charge and
spin density waves (CDW, SDW) and charge separation (CS). Within an extended Hubbard model at half filling studied by exact
numerical diagonalization, we demonstrate that the ground state phase diagram comprises, besides conventional critical lines
separating states characterized by different orderings (e.g. CDW, SDW, CS), critical lines separating phases with the same ordering (e.g. CDW-CDW) but with different symmetries. While the former also exist in infinite systems, the latter are specific for mesoscopic systems and directly related to a collective tunnel effect. We emphasize that, in order to construct correctly
a phase diagram for mesoscopic rings, the examination of CDW, SDW and CS correlation functions alone is not sufficient, and
one should also consider the symmetry of the wave function that cannot be broken. We present examples demonstrating that the
jumps in relevant physical properties at the conventional and new critical lines are of comparable magnitude. These transitions
could be studied experimentally e.g. by optical absorption in mesoscopic systems. Possible candidates are cyclic molecules and ring-like nanostructures of quantum
dots.
Received 27 November 2000 相似文献
6.
F. Gervais N. Petit C. Popon P. Buvat 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):47-52
The reflectivity spectrum of a polyaniline CSA-doped in presence of m-cresol has been measured over the wide wavenumber range
25-15,000 cm-1 (0.003-1.9 eV) for three different doping levels. Since spectra cannot be fitted correctly with the conventional Drude model,
several extensions are tested. A model derived from the factorized form of the dielectric response and including the effect
of Anderson localization in disordered metals, is proposed and found to yield good fit to data with a satisfactory physical
meaning. Data are reduced to a small number of parameters potentially useful for further comparison with other conducting
polymers or even other non-Drude conducting media like oxides.
Received 6 February 2002 / Received in final form 12 August 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: gervais@delphi.phys.univ-tours.fr
RID="b"
ID="b"UMR 6157 CNRS/CEA 相似文献
7.
Q. Yuan T. Nunner T. Kopp 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):37-42
Based on a half-filled two-dimensional tight-binding model with nearest-neighbour and next nearest-neighbour hopping the effect
of imperfect Fermi surface nesting on the Peierls instability is studied at zero temperature. Two dimerization patterns corresponding
to a phonon vector (π,π) are considered. It is found that the Peierls instability will be suppressed with an increase of next
nearest-neighbour hopping which characterizes the nesting deviation. First and second order transitions to a homogeneous state
are possible. The competition between the two dimerized states is discussed.
Received 22 December 2000 相似文献
8.
D. Mannix P.C. de Camargo C. Giles A.J.A. de Oliveira F. Yokaichiya C. Vettier 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):19-25
We report on X-ray magnetic diffraction studies of the spin density wave antiferromagnetism formed in the conduction electron
band of chromium. Non-resonant X-ray magnetic scattering was used to directly determine that chromium has zero orbital magnetisation.
Furthermore, the azimuthal dependence of this scattering provides unique evidence that chromium forms a linearly polarised
wave. In the vicinity of the K absorption edge, resonant X-ray magnetic scattering was observed. A consistent model of the
magnetic scattering has been derived from the resonant and non-resonant magnetic amplitudes. The enhancement of the magnetic
intensity arises primarily from dipole transitions from the core 1s level to 4p states. Quadrupole transitions to the magnetic 3d states are essentially non-existent due to their sensitivity to (and the absence of) orbital moment. This effect is predicted
from atomic considerations of the 3d5 ( = 0) transition metal ions.
Received 22 September 2000 相似文献
9.
D. Starešinić A. Kiš K. Biljaković B. Emerling J. W. Brill J. Souletie H. Berger F. Lévy 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):71-77
Specific heats of the charge-density-wave compounds o-TaS3 and (TaSe4)2I have been measured over the wide temperature interval 10 K-300 K. Both systems exhibit strong non-Debye behavior. Very weak
and broad anomalies are observed at the Peierls transition temperatures. For o-TaS3, the change in the curvature of the specific heat occurs at temperature of 40 K where glass transition has been deduced from
dielectric measurements, and an extended scaling analysis suggests that the glass transition is associated with a dynamical
cross over in length scales. We briefly discuss the characteristics and physical origins of the anomalies at both the Peierls
and glass transitions.
Received 5 April 2002 / Received in final form 28 June 2002 Published online 17 September 2002 相似文献
10.
11.
P. Bonville J.A. Hodges M. Shirakawa M. Kasaya D. Schmitt 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):349-355
Orthorhombic EuPdSb is known to undergo two magnetic transitions, at 12 K and at T
N≃ 18 K, and in phase III (T < 12 K), single crystal magnetisation data have shown that the spin structure is collinear antiferromagnetic, with magnetic
moments along the crystal a axis. From a 151Eu M?ssbauer absorption study, we show that, at any temperature within phase III, all the moments have equal sizes, and that
in phase II (12 K< T <18 K) the magnetic structure is modulated and incommensurate with the lattice spacings. The modulation is close to a pure
sine-wave just below T
N = 18 K, and it squares up as temperature is lowered. We measured the thermal variations of the first and third harmonics
of the moment modulation, and we could determine the first and third harmonics of the exchange coupling. We furthermore show
that the antiferromagnetic-incommensurate transition at 12 K is strongly first order, with a hysteresis of 0.05 K, and that
the incommensurate-paramagnetic transition at 18 K is weakly first order. Finally, we present an explanation of the spin-flop
transition observed in the single crystal magnetisation data in phase III when || in terms of an anisotropic molecular field tensor.
Received 17 January 2001 and Received in final form 20 March 2001 相似文献
12.
The optical properties of the quarter-filled single-band CDW systems
have been reexamined in the model with the electron-phonon coupling
related to the variations of electron site energies.
It appears that the indirect, electron-mediated coupling
between phase phonons and external electromagnetic fields
vanishes for symmetry reasons, at variance with the infrared selection
rules used in the generally accepted microscopic theory.
It is shown that the phase phonon modes and the electric fields
couple directly, with the coupling constant proportional to the
magnitude of the charge-density wave.
The single-particle contributions to the optical
conductivity tensor are determined for the ordered CDW state
and the related weakly doped metallic state by means of the Bethe-Salpeter
equations for elementary electron-hole excitations.
It turns out that this gauge-invariant approach establishes
a clear connection between the effective numbers of residual,
thermally activated and bound charge carriers.
Finally, the relation between these numbers and the activation energy of dc
conductivity and the optical CDW gap scale is explained in the way consistent
with the conductivity sum rules. 相似文献
13.
P. Roussel P. Foury-Leylekian B. Domengès D. Groult P. Labbé J.-P. Pouget 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):497-508
A new variety of P
4
W
10
O
38
, m
= 5 member of the monophosphate tungsten-bronze family with pentagonal tunnels (MPTB
p), , has been isolated and studied by X-ray diffraction measurements. The structure has been solved by direct methods from single
crystal X-ray data. The monoclinic unit cell corresponds to a regular stacking of WO
3
-type slabs which are all five-WO
6
-octahedra thick and connected through PO
4
tetrahedra. This structure is comparable to that previously described for the MPTB
p'series with m
= 4 (P
4
W
8
O
32
) and m
= 6 (P
4
W
12
O
44
). An X-ray diffuse scattering investigation has revealed that this member is subjected to charge density wave instabilities
(CDW) located on chains running along the directions. Two CDW transitions have been observed at and , bearing some resemblance with those exhibited by the m
= 4 member. The corresponding modulation wave vectors can be accounted for by a hidden nesting mechanism which connects the crossing
points of differently oriented quasi-planar Fermi surfaces, as found for the low m (4 and 6) members of the MPTB's.
Received 12 March 1999 and received in final form 20 May 1999 相似文献
14.
V. Vescoli J. Favand F. Mila L. Degiorgi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):149-154
The validity of the optical sum rules has been addressed eversince and was always matter of debate. Particularly controversial
is the proof that the partial sum rules can be extended to both optical conductivity and energy loss function. We show in this paper that for both transverse
(optical conductivity) and longitudinal (energy loss function) absorption processes the corresponding sum rule can be theoretically
established and through appropriate conditions for the integration limits exactly verified. We also focus our attention on
the one-dimensional case within the microscopic Hubbard model. An application of these concepts to the quasi one-dimensional
systems, for which we have chosen the organic (TMTSF)2PF6 material, will also be presented.
Received: 19 December 1997 / Received in final form: 9 March 1998 / Accepted: 23 March 1998 相似文献
15.
J. Dumas C. Hess C. Schlenker G. Bonfait E. Gomez Marin D. Groult J. Marcus 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):73-82
The monophosphate tungsten bronzes (PO
2
)
4
(WO
3
)
2m
are quasi-two-dimensional conductors which show charge density wave type electronic instabilities. We report electrical resistivity
and magnetoresistance measurements down to 0.30 K and in magnetic fields up to 16 T for the m
= 7, 8 and 9 members of this family. We show that these compounds exhibit at low temperature an upturn of resistivity and field
dependences of the magnetoresistance characteristic of localization effects. We discuss the dimensionality of the regime of
localization as m is varied. We show that for m
=7, the regime is quasi-two-dimensional and three-dimensional for m
= 8, 9.
Received 16 September 1999 相似文献
16.
S.V. Dordevic D.N. Basov R.C. Dynes B. Ruzicka V. Vescoli L. Degiorgi H. Berger R. Gaál L. Forró E. Bucher 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):15-23
We present a comprehensive analysis of the optical constants of the two-dimensional dichalcogenide materials 2
H
-
TaSe
2
and 2
H
-
NbSe
2
, in an attempt to address the physics of two-dimensional correlated systems. The title compounds were studied over several
decades in frequency, from the far-infrared to the ultraviolet. Measurements with linearly polarized light have allowed us
to obtain both the in-plane and out-of-plane components of the conductivity tensor. Although the electromagnetic response
of dichalcogenides is strongly anisotropic, both the in-plane and out-of-plane components of the conductivity tensor share
many common features, including the presence of a well-defined metallic component, as well as a “mid-infrared band”. We discuss
the implications of these results in the context of the spectroscopic results of other classes of low-dimensional conductors
such as the high-temperature superconducting cuprates. In particular, the analysis of the redistribution of the spectral weight
as a function of temperature, as well as the behavior of the quasiparticles relaxation rate, points to significant distinctions
between the charge dynamics of dichalcogenides and other classes of low dimensional conductors.
Received 28 October 2002 / Received in final form 10 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: degiorgi@solid.phys.ethz.ch 相似文献
17.
W.Z. Wang K.L. Yao 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):437-441
A ferrimagnetic polymer with m-phenylene skeleton as coupling unit is studied with the Hubbard model in the self-consistent mean-field theory. The ferrimagnetic
ground state with a total spin S = 1 per unit cell is obtained and originates from the antiferromagnetic correlations between the nearest neighbors. If the
on-site electron-electron repulsions at the radical sites and at the phenylene ring sites are different, the gap in energy
band structure may disappear and the ferrimagnetic ground state becomes unstable. The charge density and spin density can
transfer between the radical sites and the phenylene ring sites due to the competition between the hopping integral and the
on-site repulsion at different sites.
Received 15 July 2002 Published online 31 December 2002 相似文献
18.
B. Bourahla A. Khater R. Tigrine 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):343-349
This paper describes a theoretical study, at a microscopic scale, of the
properties of a symmetric magnetic nanocontact. In particular, we study a
symmetric nanocontact separating two waveguide groups of semi-infinite spin
ordered ferromagnetic monatomic chains. The individual and total conductance
of bulk magnons of the chains, scattering coherently at the nanocontact, and
the localised density of spin states in the nanocontact domain, are
calculated and analysed. The inter-atomic magnetic exchange is varied on the
nanocontact to investigate the consequences of magnetic softening and
hardening for the calculated properties. Transmission and reflection
scattering cross sections are calculated from elements of a Landauer type
scattering matrix. The results highlight the localized spin states on the
nanocontact domain and their interactions with incident magnons. The results
demonstrate also the magnetic and symmetry properties of the nanocontact
domain. 相似文献
19.
20.
S. Sahling J. C. Lasjaunias R. Mélin P. Monceau G. Reményi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):9-17
We have investigated the effect of the magnetic field (B) on the very
low-temperature equilibrium heat capacity ceq of the quasi-1 D organic
compound (TMTTF)2Br, characterized by a commensurate Spin Density
Wave (SDW) ground state. Below 1 K, ceq is dominated by a Schottky-like
AST-2 contribution, very sensitive to the experimental time scale,
a property that we have previously measured in numerous DW compounds. Under
applied field (in the range 0.2–7 T), the equilibrium dynamics, and hence
ceq extracted from the time constant, increases enormously. For B
≥ 2–3 T, ceq varies like B2, in agreement with a
magnetic Zeeman coupling. Another specific property, common to other
Charge/Spin density wave (DW) compounds, is the occurrence of metastable
branches in ceq, induced at very low temperature by the field exceeding
a critical value. These effects are discussed within a generalization to
SDWs in a magnetic field of the available Larkin-Ovchinnikov local model of
strong pinning. A limitation of the model when compared to experiments is
pointed out. 相似文献