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1.
We consider a model in which an electric field induces quantum nucleation of kink-antikink pairs in a pinned charge or spin density wave. Pair nucleation events, prevented by Coulomb blockade below a pair creation threshold, become correlated in time above threshold. The model provides a natural explanation for the observed (i) small density wave polarization below threshold in NbSe (3), (ii) narrow band noise, (iii) coherent oscillations, and (iv) mode-locking at high drift frequencies. 相似文献
2.
We investigate collective effects
in the strong pinning model of disordered charge
and spin density waves (CDWs and SDWs) in connection with heat relaxation
experiments.
We discuss the classical and quantum limits that
contribute to two distinct contribution to the specific heat (a Cv
T-2 contribution and a Cv T contribution respectively),
with two different types of disorder (strong pinning versus
substitutional impurities).
From the calculation of the two level system energy splitting distribution
in the classical limit
we find no slow relaxation
in the commensurate case and a broad spectrum of relaxation times
in the incommensurate case. In the commensurate case quantum effects
restore a non vanishing energy relaxation, and
generate stronger disorder
effects in incommensurate systems.
For substitutional disorder we obtain
Friedel oscillations
of bound states close to the Fermi energy.
With negligible interchain couplings
this explains the power-law specific heat Cv T
observed in experiments on CDWs and SDWs
combined to the power-law susceptibility
(T)T-1+ observed in the CDW o-TaS3. 相似文献
3.
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
4.
5.
W. Wonneberger 《Zeitschrift für Physik B Condensed Matter》1988,72(4):445-454
The Fukuyama-Lee theory for the ac response () of weakly pinned charge density waves is extended to include thermal fluctuations. The equation of motion for the local phase includes an extrinsic damping and a distinction is made between static and dynamic parameters in it. It is split into static, thermally fluctuating and response contributions to the phase, respectively. The static problem is treated using a result from Feigel'man's theory which provides a revised value for the weak pinning constant. The impurity averaging of the response equation is performed using the simplifying statistical properties of the stochastic pinning force following Bleher's recent work. The main emphasis is on the treatment of the thermal fluctuations via a thermal field
th. The non-linear Langevin equation for
th is linearized and further simplified by an RPA type approximation which eliminates the impurity fluctuations from
th. The resulting equation is solved exactly. It is shown that the correlation function of the thermal field decays initially with a short time constant. This allows to treat the thermal fluctuations on an equal footing with the impurity fluctuations in the self-consistent Born approximation. The main contribution of the thermal fluctuations results in powers of a thermal factor exp(-
th
2
/2) to the first and second order self energies of the phason Green's function. Numerical results due to these modifications are given for (,T). It is found that the absorption peak in Re () broadens and shifts to lower frequencies when the temperature is raised. The corresponding treatment for three spatial dimensional is indicated. The thermal factor is evaluated for this case and differences to Maki's result are noted. The questions of analyticity and conductivity sum rule are also dealt with.Dedicated to Professor Helmut Reik on the occasion of his 60th birthday 相似文献
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9.
At low temperatures, the spin-spin relaxation mechanism in PrCl3 is caused by the fluctuating electric-field gradients due to the transverse Pr moments. In this paper, a finite-chain calculation for the transverse autocorrelation function Sxx(q,ω) has been performed and evaluated in the temperature range kT/J < 4. Qualitative agreement is found for the temperature dependence of the spin-spin relaxation time, and an explanation is proposed for the deviations observed. 相似文献
10.
We discuss the possibility of the coexistence of spin density waves (antiferromagnetism) and triplet superconductivity as a particular example of a broad class of systems where the interplay of magnetism and superconductivity is important. We focus on the case of quasi-one-dimensional metals, where it is known that antiferromagnetism is in close proximity to triplet superconductivity in the pressure versus temperature phase diagram. Over a range of pressures, we propose an intermediate nonuniform phase consisting of antiferromagnetic and triplet superconducting orders. In the coexistence region, we propose a flop transition in the spin density wave order parameter vector, which affects the nature of the superconducting state and leads to the appearance of several new phases. 相似文献
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12.
We consider lattice spin systems with short range but random and unbounded interactions. We give criteria for ergodicity of spin flip dynamics and estimate the speed of convergence to the unique invariant measure. We find for this convergence a stretched exponential in time for a class of directed dynamics (such as in the disordered Toom or Stavskaya model). For the general case, we show that the relaxation is faster than any power in time. No assumptions of reversibility are made. The methods are based on relating the problem to an oriented percolation problem (contact process) and (for the general case) using a slightly modified version of the multiscale analysis of e.g. Klein (1993). 相似文献
13.
B. Dóra A. Virosztek 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):167-178
We consider the possibility of formation of an unconventional spin density wave (USDW) in quasi-one-dimensional electronic
systems. In analogy with unconventional superconductivity, we develop a mean field theory of SDW allowing for the momentum
dependent gap Δ() on the Fermi surface. Conditions for the appearance of such a low temperature phase are investigated. The excitation spectrum
and basic thermodynamic properties of the model are found to be very similar to those of d-wave superconductors in spite of the different topology of their Fermi surfaces. Several correlation functions are calculated,
and the frequency dependent conductivity is evaluated for various gap functions. The latter is found to reflect the maximum
gap value, however with no sharp onset for absorbtion.
Received 19 February 2001 相似文献
14.
The current-voltage characteristics (CVC) are calculated for the Josephson, interference, and quasiparticle components of
the current through a tunneling junction formed by two superconductors with spin density waves (SDW). The treatment is based
on the model of partial dielectrization (gapping) of the Fermi surface and the assumption of pinning of the spin density waves.
The following particular cases are studied in detail: asymmetric SDW superconductor-ordinary superconductor junctions and
symmetric junctions between two identical SDW superconductors. The positions and nature of the singularities in the CVC are
determined. For a symmetric contact the possibility of the existence of asymmetric CVC’s is predicted. The calculations are
in qualitative agreement with the experimentally observed behavior of the CVC’s of tunneling junctions and microcontacts containing
the SDW superconductor with heavy fermions URu2Si2.
Fiz. Tverd. Tela (St. Petersburg) 41, 1743–1749 (October 1999) 相似文献
15.
An interlayer tunneling technique has been used for spectroscopy of charge density wave (CDW) energy gaps (Δ1,2) in NbSe3 subsequently opened at the Fermi surface on decreasing temperature at T
p1 = 145 K (CDW1) and at T
p2 = 60 K (CDW2). We found that the CDW2 formation is accompanied by an increase of the CDW1 gap below T
p2. The maximum enhancement of Δ1, δΔ1 is about 10%. The effect observed has been predicted theoretically as resulting from the joint phase locking of both CDWs
with the underlying crystalline lattice below T
p2.
The text was submitted by the authors in English. 相似文献
16.
Quantum correlations dynamics of three-qubit states coupled to an XY spin chain: Role of coupling strengths 下载免费PDF全文
We investigate the prominent impacts of coupling strengths on the evolution of entanglement and quantum discord for a three-qubit system coupled to an XY spin-chain environment. In the case of a pure W state, more robust, even larger nonzero quantum correlations can be obtained by tailoring the coupling strengths between the qubits and the environment.For a mixed state consisting of the GHZ and W states, the dynamics of entanglement and quantum discord can characterize the critical point of quantum phase transition. Remarkably, a large nonzero quantum discord is generally retained, while the nonzero entanglement can only be obtained as the system-environment coupling satisfies certain conditions. We also find that the impact of each qubit's coupling strength on the quantum correlation dynamics strongly depends on the variation schemes of the system-environment couplings. 相似文献
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We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counterpropagating coherent states is ejected from the center of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the quantum kicked rotor. From this we can analyze the entanglement production and interpret the ejected coherent states as a manifestation of the so-called "accelerator modes" of a classically chaotic system. 相似文献
19.
J. L. Guo H. S. Song 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(3):791-796
The entanglement dynamics of three-qubit states under an XY spin
chain at finite temperature with three-site interaction is
investigated. It is shown that the three-site interaction does not
affect the behavior of quantum phase transition (QPT) induced by the
external magnetic field and does not induce new critical regions in
the XY model. In addition, concerned with the effect of the
three-site interaction on the entanglement evolution, we find the
three-site interaction can not only enhance but also suppress the
decay of the entanglement between the three-qubit system, which
depends on the initial states of the system and the parameters
related with the environmental spin chain. 相似文献
20.
Infrared conductivity from an incommensurate spin density wave occurs due to even-order charge density wave harmonics which interact with the host lattice. Phonon states within the density-wave-induced energy gap for single-particle excitations lead to conductivity much different from that of an incommensurate charge density wave including counter-ion ordering. The conductivity expected for relaxed and quenched states of (TMTSF)2ClO4 is discussed. 相似文献