共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Montambaux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):377-383
The stability of a Charge Density Wave (CDW) in a one-dimensional ring pierced by a Aharonov-Bohm flux is studied in a mean-field
picture. It is found that the stability depends on the parity of the number N of electrons. When the size of the ring becomes as small as the coherence length , the CDW gap increases for even N and decreases for odd N. Then when N is even, the CDW gap decreases with flux but it increases when N is odd. The variation of the BCS ratio with size and flux is also calculated. We derive the harmonics expansion of the persistent
current in a presence of a finite gap.
Received: 16 September 1997 / Received in final form: 12 November 1997 / Accepted: 13 November 1997 相似文献
2.
A. Kobelkov F. Gleisberg W. Wonneberger 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):21-27
Starting from the static Fukuyama-Lee-Rice equation for a three-dimensional incommensurate charge density wave (CDW) in quasi
one-dimensional conductors a solvable model for local phase pinning by impurities is defined and studied. We find that average
CDW energy and average pinning force show critical behaviour with respect to the pinning parameter h. Specifically the pinning force exhibits a threshold at h=1 with exponent . Our model exemplifies a general concept of local impurity pinning in which the force exerted by the impurity on the periodic
CDW structure becomes multivalued and metastable states appear beyond a threshold. It is found that local impurity pinning
becomes less effective at low temperatures and may eventually cease completely. These results are independent of spatial dimensionality
as expected for local impurity pinning. Comparison with Larkin's model is also made.
Received 8 July 1998 相似文献
3.
M. Pinterić T. Vuletić M. Lončarić S. Tomić J.U. von Schütz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):487-493
We report a detailed characterization of an unique 3-fold commensurate insulating state in single crystals of the organic
– inorganic d hybrid Cu(DMe-DCNQI)2 systems with deuterated and partially deuterated DCNQI ring, by means of low-frequency dielectric spectroscopy. A broad relaxation
mode of strength centred at kHz is observed in the hysteresis temperature region in which the insulating phase coexists with metallic islands. At lower
temperatures, outside the nucleation range, the relaxation narrows, approaching a Debye-like form for an overdamped response
of a system with a single degree of freedom. Both, the relaxation strength and the mean relaxation time () are much larger than that expected for single-particle excitations. These features suggest the origin of the dielectric
relaxation as an intrinsic property of the N = 3 charge density wave state.
Received 1 December 1999 and Received in final form 5 April 2000 相似文献
4.
The spin-1/2 Heisenberg chain: thermodynamics, quantum criticality and spin-Peierls exponents 总被引:1,自引:0,他引:1
A. Klümper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):677-685
We present numerical and analytical results for the thermodynamical properties of the spin-1/2 Heisenberg chain at arbitrary
external magnetic field. Special emphasis is placed on logarithmic corrections in the susceptibility and specific heat at
very low temperatures (T/J=10-24) and small fields. A longstanding controversy about the specific heat is resolved. At zero temperature the spin-Peierls exponent
is calculated in dependence on the external magnetic field. This describes the energy response of the system to commensurate
and incommensurate modulations of the lattice. The exponent for the spin gap in the incommensurate phase is given.
Received: 12 February 1998 / Received in final form: 15 March 1998 / Accepted: 17 March 1998 相似文献
5.
U. Beierlein C. Hess C. Schlenker J. Dumas R. Buder D. Groult E. Steep D. Vignolles G. Bonfait 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):215-226
Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional
monophosphate tungsten bronzes (PO2)4(WO3)2m for m
=5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density
instability (CDW) at 160 K and a possible second one at 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen
oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW
gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent
with a change of the Fermi surface below 30 K.
Received 23 November 1999 and Received in final form 23 March 2000 相似文献
6.
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
7.
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
8.
H. Guyot J. Dumas M. V. Kartsovnik J. Marcus C. Schlenker I. Sheikin D. Vignolles 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(1):25-30
The purple molybdenum bronze KMo6O17 is a quasi-two-dimensional
compound which shows a Peierls transition towards a commensurate metallic
charge density wave (CDW) state. High magnetic field measurements have
revealed several transitions at low temperature and have provided an unusual
phase diagram “temperature-magnetic field”. Angular studies of the
interlayer magnetoresistance are now reported. The results suggest that the
orbital coupling of the magnetic field to the CDW is the most likely
mechanism for the field induced transitions. The angular dependence of the
magnetoresistance is discussed on the basis of a warped quasi-cylindrical
Fermi surface and provides information on the geometry of the Fermi surface
in the low temperature density wave state. 相似文献
9.
D. Staresinic A. Borovac K. Biljakovic H. Berger F. Levy J.W. Brill 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):425-429
We report on measurements of the voltage dependence of the complex shear compliance of two crystals of the charge-density-wave
(CDW) conductor NbSe3, for torsional frequencies between 1 Hz and 71 Hz. For both samples, there is a frequency independent, ∼1% increase of the magnitude of the compliance when the voltage exceeds the threshold for CDW depinning, but the internal
friction has a striking sample dependence which we do not understand. For one sample, there is a frequency independent decrease
in internal friction with CDW depinning, suggesting that the elastic changes are not relaxational and might reflect changes
in the screening of the crystal strain by the CDW. For the second sample, the sign and magnitude of the change in internal
friction is strongly frequency dependent, which we associate with a change in screening due to the finite electron diffusion
time. The second sample also exhibits a frequency dependent peak in internal friction near threshold that may reflect relaxation
of the CDW phase.
Received 14 August 2001 and Received in final form 3 October 2001 相似文献
10.
S. Fujimoto N. Kawakami 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):389-393
The effects of Umklapp scattering on the zero-temperature conductance in one-dimensional quantum wires are reexamined by taking
into account both the screening of external potential and the non-uniform chemical potential shift due to electron-electron
interaction. It is shown that in the case away from half-filling the conductance is given by the universal value, 2e
2
/h, even in the presence of Umklapp scattering, owing to these renormalization effects of external potential. The conclusion
is in accordance with the recent claim obtained for the system with non-interacting leads being attached to a quantum wire.
Received: 5 February 1998 / Received in final form: 16 March 1998 / Accepted: 17 April 1998 相似文献
11.
12.
P. Foury-Leylekian J.P. Pouget M. Greenblatt E. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):157-167
We present a structural investigation of the family of quasi-one-dimensional (quasi-1D) conductors, which exhibit intriguing charge transport properties where, for x small, the conductivity exhibits a crossover from a semiconducting to a metallic like regime when the temperature decreases.
In these materials the double zig-zag chains, together with the diphosphate groups, delimit channels which are partially filled with the ions. It is found, from an X-ray diffuse scattering investigation, that at room temperature the ions are locally ordered on a lattice of well-defined sites in the channel direction and not ordered between neighboring
channels. These ions form 1D incommensurate concentration waves whose periodicity depends on the stoichiometry. In upon cooling, the intrachannel order increases significantly, and an interchannel order between the 1D concentration waves develops. But, probably because of kinetic effects, no tridimensional (3D) long range order of the ions is achieved at low temperature. The 3D low-temperature local order has been determined and it is found that the phase
shift between the concentration waves minimizes their Coulomb repulsions. This local order is increasingly reduced as the Cs concentration
diminishes. We interpret the intriguing features of the electrical conductivity in relationship with the thermal evolution
of the Cs ordering effects. We suggest that in , for x small, a localization-delocalization transition of the Anderson type occurs due to the thermal variation of the Cs disorder.
When x increases, the enhancement of the disorder leads to a localization of the electronic wave function in the whole temperature
range measured. Finally, and probably because of the disorder, no charge density wave instability is revealed by our X-ray
diffuse scattering investigation.
Received: 10 October 1997 / Received in final form: 11 December 1997 /
Accepted: 16 December 1997 相似文献
13.
Y.I. Latyshev B. Pannetier P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):421-426
We demonstrate for the first time that a periodic array of submicrometer holes (antidots) can be patterned into thin single
NbSe3 crystals. We report on the study of Charge Density Wave (CDW) transport of the network of mesoscopic units between antidots.
Size of the elementary unit can be as small as 0.5 μm along the chain axis and in cross-section. We observe size effects for Ohmic residual resistance and in CDW transport current-voltage characteristics
in submicronic networks.
Received: 25 November 1997 / Received in final form: 30 March 1998 / Accepted: 6 April 1998 相似文献
14.
S. Duhot R. Mélin 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):289-296
A Cooper pair from a s-wave superconductor (S) entering a conventional charge density wave (CDW) below the Peierls gap dephases
on the Fermi wavelength while one particle states are localized on the CDW coherence length ξCDW. It is thus practically impossible to observe a Josephson current through a CDW. The paths following different sequences
of impurities interfere destructively, due to the different electron and hole densities in the CDW. The same conclusion holds
for averaging over the conduction channels in the ballistic system. We apply two microscopic approaches to this phenomenon:
(i) a Blonder, Tinkham, Klapwijk (BTK) approach for a single highly transparent S-CDW interface; and (ii) the Hamiltonian
approach for the Josephson effect in a clean CDW and a CDW with non magnetic disorder. The Josephson effect through a spin
density wave (SDW) is limited by the coherence length ξSDW, not by the Fermi wave-length. A Josephson current through a SDW might be observed in a structure with contacts on a SDW
separated by a distance ξSDW. 相似文献
15.
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
16.
17.
K. Batra V. Prasad M. Mohan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):191-198
The scattering of heavy ion with a multilevel Rydberg atom in the presence of an electromagnetic field is studied. The interaction
of Rydberg atom and the e.m field is explored using non-perturbative quasi-energy technique. Although the results are presented
for selected excitations but in actual calculations we have included many levels of the atom. The effect of various parameters
are shown on collisional excitation process. As an illustration detailed calculations are performed for the inelastic proton-Na
Rydberg atom collision accompanied by the transfer of photons and the effects of dressing due to the field are considered.
The emphasis of the present work is on collision induced transitions especially the case that involves change of orbital as
well as principal quantum number.
Received 26 December 2001 / Received in final form 8 April 2002 Published online 19 July 2002 相似文献
18.
M. Sassetti F. Napoli B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):643-654
Using the bosonization technique, a theory for the collective excitations of the interacting electrons in quantum wires with
two subbands occupied is developed. The dispersion relations for the inter-subband charge and spin density excitations are
determined. The results are used to interpret the features observed in recent measurements of the Raman spectra of AlGaAs/GaAs
quantum wires, particularly for photon energies near band gap resonance. It is shown that peaks previously identified as “single
particle excitations” are signatures of higher order collective spin density excitations. Predictions about the observability
of the interband modes are made.
Received 8 February 1999 相似文献
19.
A.-S.F. Obada A.M. Abdel-Hafez M. Abdelaty 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):289-294
Phase properties of the field interacting with a two-level atom in a lossless cavity Jaynes-Cummings model, taking into account
the level shifts produced by Stark effect with an additional Kerr medium for one-mode are studied using the phase formalism
of Pegg and Barnett. It is shown in particular that phase properties of the field reflect the collapse and revival phenomena.
The results for the time evolution of the phase probability distribution and the phase fluctuations are obtained. The effect
of Stark shift on the phase properties in both the absence and presence of a Kerr medium is analyzed. Phase localization is
found for certain choice of the parameters.
Received: 27 March 1998 / Revised: 8 June 1998 / Accepted: 9 June 1998 相似文献
20.
H. Stein C. Porthun G. Röpke 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):393-398
For fermionic model systems with a separable interaction the BCS equations are solved self-consistently. In addition, the
possibility of a liquid-gas phase transition is considered by inspecting thermodynamic stability. Different examples of temperature-density
phase diagrams are given depending on the parameters of a model interaction. In particular, a liquid-gas binodal anomaly is
found due to the superposition of the superfluid and the liquid-gas phase transition.
Received: 14 October 1997 / Accepted: 2 December 1997 相似文献