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1.
S. Petit A.H. Moudden B. Hennion A. Vietkin A. Revcolevschi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):163-167
Inelastic neutron scattering measurements have been performed on high quality single crystals of in order to study the spin dynamics of this compound. In addition to the well-established incommensurate magnetic response,
we show the existence of a new set of low energy excitations present in the whole superconducting region of the phase diagram.
This new feature of the dynamical cross section is characterized, below about 10 K, by very short range ( lattice spacing) antiferromagnetic correlations and by a low energy scale of meV. At higher temperatures these fluctuations become nearly Q-independent. Different possible origins of these new spin correlations are discussed.
Received: 3 September 1997 / Revised: 21 November 1997 / Accepted: 26 January 1998 相似文献
2.
R. Lacaze A. Morel B. Petersson J. Schröper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):509-523
We present an investigation of the 2D attractive Hubbard model, considered as an effective model relevant to superconductivity
in strongly interacting electron systems. We use both hybrid Monte-Carlo simulations and existing hopping parameter expansions
to explore the low temperature domain. The increase of the static S-wave pair correlation with decreasing temperature, which depends weakly on the band filling in the explored temperature range,
is analyzed in terms of an expected Kosterlitz-Thouless superconducting transition. Using both our data and previously published
results, we show that the evidence for this transition is weak: If it exists, its temperature is very low. The number of unpaired
electrons remains nearly constant with temperature at fixed attractive potential strength. In contrast, the static magnetic
susceptibility decreases fast with temperature, and cannot be related only to pair formation. We introduce a method by which
the Padé approximants of the existing series for the susceptibility give sensible results down to rather low temperature region,
as shown by comparison with our numerical data.
Received: 30 October 1996 / Revised: 23 October 1997 / Accepted: 29 January 1998 相似文献
3.
C. Stockinger W. Markowitsch W. Lang W. Kula R. Sobolewski 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):301-311
We report our studies on the superconducting and normal-state properties of metallic thin films ( 52 K) exposed to long-term white-light illumination (photodoping). It was observed that the effects of photoexcitation strongly
depended on the temperature at which the photodoping was performed. At low temperatures, both the Hall mobility and the Hall
number were photoenhanced, whereas, at temperatures slightly below room temperature, the Hall mobility initially showed an
abrupt increase followed by a long-term decrease, and the Hall number increased even stronger than at low temperatures. The
enhancement of the film's superconducting transition temperature Tc, caused by photodoping, exhibited the same temperature dependence as the enhancement of the Hall number, being largest ( 2.6 K) at high temperatures. From the asynchronous behavior of the Hall quantities, we conclude that both the photoassisted
oxygen ordering and charge transfer mechanisms contribute to photodoping. The relative contributions of both mechanisms and,
thus, the electronic properties of the photoexcited state are strongly temperature dependent. Studies of the relaxation of
the photoexcited state at 290 K showed an unexpectedly short relaxation time of the Hall mobility after termination of the
illumination. The relaxation saturated somewhat below the initial, undoped value, similarly to the decrease of the Hall mobility,
observed upon long illumination. These latter findings give evidence for a competition between the oxygen ordering and thermal
disordering processes during and after the photoexcitation in the high-temperature range.
Received: 13 October 1997 / Accepted: 19 November 1997 相似文献
4.
C. Stockinger G. Heine W. Markowitsch W. Lang R. Adam R. Sobolewski R. Rössler J.D. Pedarnig D. Bäuerle 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):227-231
() thin films were photodoped with white light at various temperatures from 70 K to 290 K. Before and after the excitation,
the magnetoconductivity was measured in a magnetic field B
= 0.5 T, and the experimental results were fitted to the Aslamazov-Larkin theory of superconducting order-parameter fluctuations
to determine the superconducting coherence lengths, and . We observed that the photodoping process enhanced and and that the amount increased with the photodoping temperature increase. On the other hand, the superconducting anisotropy
/ decreased with increasing temperature. The photodoping effect enhances superconducting properties of partially oxygen-deficient
samples and is considerably increased by high doping temperatures.
Received 15 December 1999 and Received in final form 24 May 2000 相似文献
5.
X.L. Lei H.L. Cui 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):513-518
We suggest a balance-equation approach to hot-electron transport in a single arbitrary energy band subject to an intense radiation
field of terahertz (THz) frequency, including all the multiphoton emission and absorption processes and taking account of
realistic scatterings due to impurities and phonons. This approach, which allows one to calculate THz-driving, time-averaging
transport based on a set of time-independent equations, provides a convenient method to study the effect of an intense THz
electric field on carrier transport in a nonparabolic energy band. As an example, these fully three-dimensional, acceleration-
and energy-balance equations are applied to the discussion of superlattice miniband transport at lattice temperature T=77 and 300 K driven by the THz radiation field of varying strengths. It is shown that the current through a dc biased miniband
superlattice is greatly reduced by the irradiation of an intense THz electric field.
Received: 23 January 1998 / Revised: 31 March 1998 / Accepted: 20 April 1998 相似文献
6.
S. Chakravarty 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):337-343
The interlayer tunneling mechanism of the cuprate high temperature superconductors involves a conversion of the confinement
kinetic energy of the electrons perpendicular to the CuO-planes (c-axis) in the normal state to the pair binding energy in the superconducting state. This mechanism is discussed and the arguments
are presented from the point of view of general principles. It is shown that recent measurements of the c-axis properties support the idea that the electrons substantially lower their c-axis kinetic energy upon entering the superconducting state, a change that is nearly impossible in any conventional mechanism.
The proper use of a c-axis conductivity sum rule is shown to resolve puzzles involving the penetration depth and the optical measurements.
Received: 5 January 1998 / Accepted: 17 March 1998 相似文献
7.
N.N. Garif'yanov Y.V. Goryunov T. Mühge L. Lazar G.G. Khaliullin K. Westerholt I.A. Garifullin H. Zabel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):405-407
We have studied superconducting and magnetic properties of sputtered Fe/Pb/Fe-trilayers. For a fixed Pb thickness and with changing Fe thickness, , a monotonic decrease of the superconducting transition temperature was observed. Magnetization measurements clearly showed that Fe remains ferromagnetic down to the monolayer range. A quantitative
comparison of with the theory of pair breaking by the exchange field reveals that the observed -suppression by the ferromagnetic Fe-layer is much weaker than expected. Possible reasons for the reduced -suppression in this system are discussed.
Received: 30 June 1997 / Revised: 20 August 1997 / Accepted: 16 December 1997 相似文献
8.
A. Trovato J. van Mourik A. Maritan 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):63-73
A lattice model of a hetero-polymer with random hydrophilic-hydrophobic charges interacting with the solvent is introduced,
whose continuum counterpart has been proposed by Garel, Leibler and Orland [#!GLO!#]. The transfer matrix technique is used
to study various constrained annealed systems which approximate at various degrees of accuracy the original quenched model.
For highly hydrophobic chains an ordinary -point transition is found from a high temperature swollen phase to a low temperature compact phase. Depending on the type
of constrained averages, at very low temperatures a swollen phase or a coexistence between compact and swollen phases are
found. The results are carefully compared with the corresponding ones obtained in the continuum limit, and various improvements
in the original calculations are discussed.
Received: 10 April 1998 / Revised: 4 June 1998 / Accepted: 1st July 1998 相似文献
9.
10.
T. Ohm C. Sangregorio C. Paulsen 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):195-199
We observed non-exponential relaxation for a quantum tunneling molecular magnetic system at very low temperatures and argue
that it results from evolving intermolecular dipole fields. At the very beginning of the relaxation, the magnetization follows
a square-root time dependence. A simple model is developed for the intermediate time range that is in good agreement with
the data over 4 decades in time. Detailed numerical calculations as well as measurements are presented which indicate unusual
correlation effects in these systems.
Received: 15 May 1998 / Revised: 10 July 1998 / Accepted: 11 July 1998 相似文献
11.
L.G. Vieira O. Hernandez A. Almeida M. Quilichini J.L. Ribeiro M.R. Chaves A. Klöpperpieper 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):447-456
We report a combined experimental study by means of elastic neutron scattering and dielectric measurements of a partially
deuterated and brominated BCCD (Betaine Calcium Chloride Dihydrate) crystal. The lowest-temperature phase is one-dimensional modulated and
characterized by the coexistence of different commensurate domains (with = 1/4, 4/17, 2/9 and 1/5 on cooling), but with a clear predominance of the five-fold phase. A huge global thermal hysteresis
of the wave-vector of the modulation, attaining values of about 9 K in the incommensurate phase and up to 15 K in the “harmless”
low temperature part of the phase diagram, is observed up to . The role of lattice defects on this phenomenon is discussed. Similarly to the behaviour of the pure compound, the structural
modulation evolves on cooling towards a soliton regime (growth of third and fifth-order satellite peaks), probably with respect
to a non-stabilized non-modulated ferroelectric phase. The critical temperatures deduced from dielectric constant and pyroelectric
current measurements are in very good agreement with those obtained from neutron scattering. The dielectric anomaly observed
in at K, and known as the “-anomaly”, could not be related with any special feature detected in the neutron data, and in particular no correlation between
this anomaly and the appearance of the soliton regime can be established.
Received 26 October 1998 相似文献
12.
M. Sellitto 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):135-138
We investigate by Monte-Carlo simulation the linear response function of three dimensional structural glass models defined
by short-range kinetic constraints and a trivial equilibrium Boltzmann-Gibbs measure. The breakdown of the fluctuation-dissipation
theorem in the glassy phase follows the prediction of mean field low temperature mode-coupling theory.
Received: 24 April 1998 / Received in final form: 8 May 1998 / Accepted: 11 May 1998 相似文献
13.
G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
14.
H.L. Liu M.A. Quijada D.B. Tanner H. Berger G. Margaritondo 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):47-56
We report on the ab-plane polarized reflectance of an untwinned single crystal over the frequency range from 80 to (10 meV-4 eV) at temperatures between 10 and 300 K. We find a clear anisotropy in the ab-plane optical conductivity above and below , which is very similar to that formerly published data of (M.A. Quijada et al., Z. Phys. B 94, 255 (1994)). We employ both the one-component and two-component analyses to the optical data, which suggest that the normal-state
infrared anisotropy of originates not only from the mass anisotropy, but also from the scattering rate anisotropy. Our results provide evidence
that the electronic structures within the plane are anisotropic. In the superconducting state, there is a definite ab-plane anisotropy to the far-infrared absorption. This anisotropy could be due either to anisotropy of the superconducting
gap or to anisotropy of the mid-infrared component to the conductivity. We also observe the superconducting condensate is
anisotropic: The value of the superconducting penetration depth in the a-direction is slightly smaller than that along the b-axis.
Received 16 July 1998 相似文献
15.
L. Piraux S. Dubois A. Fert L. Belliard 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):413-420
A theory, based on earlier work by Valet and Fert, is first presented to describe the influence of temperature on the perpendicular
giant magnetoresistance (GMR) in multilayers. Then we present GMR measurements performed at T=77 K and at room temperature on Co/Cu multilayered nanowires with layer thicknesses ranging from a few nm to 1 μm. We use
our model to obtain a good quantitative fit to the experimental results in both the short spin diffusion length limit and
out of this limit. We discuss the temperature dependence of the bulk parameters, the scattering spin asymmetry coefficient
and spin diffusion length in the Co layers.
Received: 25 January 1998 / Accepted: 6 May 1998 相似文献
16.
C.C. Tsuei T. Doderer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):257-262
The fact that the stripe phase and pseudogap in the cuprate superconductors occur in the same doping regime is emphasized.
A model based on charge confinement in self-organized nanometer-scale stripe fragments is proposed to understand various generic
features of the normal-state energy gap including the magnitude of the gap, its anti-correlation with the superconducting
gap, and the d-wave symmetry in its -dependence. This model also provides a basis for understanding other anomalous normal-state properties such as the linear
temperature dependence of electrical resistivity.
Received 7 December 1998 相似文献
17.
18.
P. Nozières F. Pistolesi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):649-662
We consider a two-dimensional semiconductor with a local attraction among the carriers. We study the ground state of this
system as a function of the semiconductor gap. We find a direct transition from a superconducting to an insulating phase for
no doping at a critical value, the single particle excitations being always gapped. For finite doping we find a smooth crossover.
We calculate the critical temperature due to both the particle excitations and the Berezinkii-Kosterlitz-Thouless transition.
Received 8 December 1998 相似文献
19.
R. Farhi M. El Marssi A. Simon J. Ravez 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):599-604
Dielectric and Raman scattering experiments were performed on various ceramics with composition Ba(Ti1-xZrx)O3. Such lead-free, environmental-friendly materials were shown, from dielectric measurements, to exhibit behaviours extending
from conventional to relaxor ferroelectrics on increasing the zirconium concentration. The evolution of the Raman spectra
was studied as a function of temperature for various compositions, and the spectroscopic signature of the corresponding phases
was determined. In the relaxor state, the variation of the integrated intensity of the Raman lines with temperature showed
a plateau at low temperature. This anomaly was also detected as a peak in depolarization current measurements, and attributed
to ergodicity breaking which characterizes usual relaxor systems. Raman results hint at locally rhombohedral polar nanoregions
resulting from the random fields associated with Zr ions.
Received 25 September 1998 相似文献
20.
J. Friedel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):409-411
Recent studies of the Fermi surface of quasi-two-dimensional organic conductors comfort the idea that the presence of a van
Hove anomaly near the Fermi level is a favourable factor for superconductivity.
Received: 28 April 1998 / Revised and accepted: 13 May 1998 相似文献