共查询到20条相似文献,搜索用时 384 毫秒
1.
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
2.
W. Westerburg F. Martin P.J.M. van Bentum J.A.A.J. Perenboom G. Jakob 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):509-513
We measured the temperature dependence of the linear high field Hall resistivity of ( K) and ( K) thin films in the temperature range from 4 K up to 360 K in magnetic fields up to 20 T. At low temperatures we find a
charge-carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature
range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature
a dramatic drop in the number of charge-carriers n down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data
due to a non saturated magnetic state will lead a more pronounced charge-carrier density collapse.
Received 22 July 1999 and Received in final form 7 October 1999 相似文献
3.
S. Bellucci P. Onorato 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):35-40
We propose a new scheme of spin filtering employing ballistic
nanojunctions patterned in a two dimensional electron gas
(2DEG). Our proposal is essentially based on the spin-orbit (SO)
interaction generated by a lateral confining potential (β-SO
coupling ).
We demonstrate that the flow of a longitudinal unpolarized current
through a ballistic T and X junction with this spin-orbit
coupling will induce a spin accumulation which has opposite signs
for the two lateral probes and is, therefore, the principal
observable signature of the spin Hall effect in these devices. 相似文献
4.
D.V. Livanov A.A. Varlamov M. Putti M.R. Cimberle C. Ferdeghini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):401-404
The fluctuation-induced magnetoconductivity of the Bi2Sr2Ca2Cu3O10+x phase is studied above zero-field critical temperature Tc(0) and for moderate magnetic fields. It is found that the Gaussian approximation for superconducting fluctuations underestimates
the negative fluctuation magnetoconductance drastically in the Tc(0) < T < Tc(0) + 20 K temperature range. Taking into account the critical fluctuation contribution on the base of self-consistent Hartree
approximation makes it possible to explain the data quantitatively in terms of the only Aslamazov-Larkin contribution for
different magnetic fields and temperatures, consistently with the zero field data.
Received 14 April 2000 and Received in final form 13 July 2000 相似文献
5.
N.A. Babushkina L.M. Belova E.A. Chistotina O.Yu. Gorbenko A.R. Kaul B. Güttler K.I. Kugel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):409-415
The effect of
16
O
→
18
O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substrates. For the films on LaAlO3, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic
field ( H
≥ 2
T) transformed the sample with 18O back to the metallic state. The films on SrTiO3 remained metallic at low temperatures for both 16O and 18O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after
16
O
→
18
O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis,
especially pronounced in the case of the films on LaAlO3. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and
charge ordering.
Received 11 February 2000 and Received in final form 13 September 2000 相似文献
6.
T.M. Mishonov N. Chéenne D. Robbes J.O. Indekeu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):291-296
The generation of harmonics of the voltage response is considered when an AC current is applied through a superconducting
film above Tc. It is shown that almost at all temperatures the mechanism of the temperature oscillations created by the AC current and
the temperature dependence of the resistance dominates over the isothermal nonlinear electric conductivity. Only in a narrow
critical region close to Tc the latter is essential for the generation of the harmonics. A detailed investigation of harmonics generation provides an
accurate method for measuring the thermal boundary conductance between the film and the insulating substrate. The critical
behaviour of the third harmonic will give a new method for the determination of the lifetime of metastable Cooper pairs above
Tc. The comparison of the calculated fifth harmonics of the voltage with the experiment is proposed as an important test for
the applicability of the employed theoretical models.
Received 8 September 2001 相似文献
7.
8.
M. Ziese R. Höhne H.C. Semmelhack H. Reckentin N.H. Hong P. Esquinazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):415-422
The magnetotransport properties of magnetite films with different microstructures were investigated in order to identify prerequisites
for the attainment of a large tunnelling magnetoresistance in polycrystalline samples. Epitaxial films on MgAl2O4, polycrystalline films on Al2O3 and rough MgAl2O4 substrates and a polycrystalline La0.7Ca0.3MnO3 film on MgO were compared. Although grain boundaries induce a large high-field magnetoresistance in magnetite films, the
low-field magnetoresistance characteristic for spin-polarized tunnelling was virtually absent in these samples. Two factors
might be responsible for this behaviour: (1) grain boundaries in magnetite are conducting and do not form tunnelling barriers
and (2) the spin-polarization near grain boundaries is suppressed due to non-stoichiometry.
Received 15 April 2002 Published online 13 August 2002 相似文献
9.
I. Kirschner R. Laiho A.C. Bódi A.D. Caplin E. Lähderanta G. Zsolt 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):389-399
Using a new starting material of Ba2Cu3O5 and a three step heat treatment, single phase Tl2Ca1Ba2Cu2O8 high- superconducting samples have been prepared, possessing the onset- and critical temperatures K and K. The morphology dependent value of is 17 Oe, 8 Oe and 5 Oe at 77 K in the case of bulk, crushed and powdered materials, respectively. The a.c. susceptibility,
r.f. susceptibility and microwave absorption properties show a significant dependence on the particle size with a sharp change
in the interval between 750 μm and 1200 μm. These experiments provide characteristic parameters for intergrain material (treated
as 3D Josephson network) as mm, Oe and A/cm2 at 77 K. The data are controlled by modulated microwave absorption measurements. The results obtained can be explained well
both by the finite size junction model and cavity mode absorption model. The Josephson network is determined unambiguously
by metallic S-N-S weak links.
Received 10 October 1998 相似文献
10.
W. Albrecht Th. Kruse K. Leo H. Kurz 《Applied Physics A: Materials Science & Processing》1993,56(5):463-465
We present a detailed investigation of the dynamics of laser-excited carriers in YBa2Cu3Ox thin films with various oxygen contents x. We observe a Fermi level shift due to oxygen reduction and determine the energy gap between the Fermi level and the upper Hubbard band. The electron-phonon coupling constant is determined as a function of transition temperature. 相似文献
11.
12.
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
13.
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
14.
J. Torrès T. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):319-322
In the light of the recent analogs of the Hanbury-Brown and Twiss experiments [1] in mesoscopic beam splitters, negative current
noise correlations are recalled to be the consequence of an exclusion principle. Here, positive (bosonic) correlations are
shown to exist in a fermionic system, composed of a superconductor connected to two normal reservoirs. In the Andreev regime,
the correlations can either be positive or negative depending on the reflection coefficient of the beam splitter. For biases
beyond the gap, the transmission of quasiparticles favors fermionic correlations. The presence of disorder enhances positive
noise correlations. Potential experimental applications are discussed.
Received 1 June 1999 相似文献
15.
A. C. Varghese C. S. Menon 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):465-468
The various electrical properties and the nature of conduction mechanisms of
magnesium phthalocyanine thin film devices with top and bottom aluminium
electrodes have been investigated. The conduction mechanism was identified
as injection limited essentially due to the electrode material. Even with
the same electrode materials, the device showed asymmetric conduction
behavior in the forward and reverse bias. In general the conduction was
interpreted as a Schottky emission with barrier height Φs=1.07 eV for
the forward bias and Φs=1.09 eV in the reverse bias. The effect of
oxygen on the conductivity of the device has also been investigated. In the
oxygen doped samples the conductivity is decreased which may be attributed
to an interfacial layer between the electrode and the organic layer. Further
in the oxygen doped sample while a Schottky emission is observed at lower
voltages Poole-Frenkel conductivity was identified in the higher voltage
region. 相似文献
16.
A. Vedyayev R. Vlutters N. Ryzhanova J.C. Lodder B. Dieny 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):5-10
We present a quantum mechanical model of the magnetoresistance in ferromagnetic tunnel junctions artificially doped by the
introduction of layers of impurities in the middle of the barrier. The electron transport across the barrier is described
by a combination of direct tunneling, tunneling assisted by spin-conserving scattering and tunneling assisted by spin-flip
scattering. With this model, we interpret recent experimental results concerning the dependence of the TMR amplitude on the
amount of impurities in the barrier and on temperature.
Received 1st February 2001 and Received in final form 14 June 2001 相似文献
17.
M. Hillenkamp G. Di Domenicantonio C. Félix L. Gravier S. Serrano-Guisan J.-P. Ansermet 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):447-449
Spin-dependent transport in granular metallic
nanostructures has been investigated by means of a thermoelectric
measurement. Cobalt clusters of well-defined size (〈n〉 = 15-600) embedded in copper and silver matrices show
magnetic field responses of up to several hundred percent at low
temperature. The experimental observations are attributed to spin
mixing. The influence of cluster size and matrix are discussed. 相似文献
18.
M. Potthoff W. Nolting 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):555-568
The correlation-driven transition from a paramagnetic metal to a paramagnetic Mott-Hubbard insulator is studied within the
half-filled Hubbard model for a thin-film geometry. We consider simple-cubic films with different low-index surfaces and film
thickness d ranging from d=1 (two-dimensional) up to d=8. Using the dynamical mean-field theory, the lattice (film) problem is self-consistently mapped onto a set of d single-impurity Anderson models which are indirectly coupled via the respective baths of conduction electrons. The impurity models are solved at zero temperature using the exact-diagonalization
algorithm. We investigate the layer and thickness dependence of the electronic structure in the low-energy regime. Effects
due to the finite film thickness are found to be the more pronounced the lower is the film-surface coordination number. For
the comparatively open sc(111) geometry we find a strong layer dependence of the quasi-particle weight while it is much less
pronounced for the sc(110) and the sc(100) film geometries. For a given geometry and thickness d there is a unique critical interaction strength U
c2
(d) at which all effective masses diverge and there is a unique strength U
c1
(d) where the insulating solution disappears. U
c2
(d) and U
c1
(d) gradually increase with increasing thickness eventually approaching their bulk values. A simple analytical argument explains
the complete geometry and thickness dependence of Uc2. Uc1 is found to scale linearly with Uc2.
Received 19 August 1998 相似文献
19.
M. Stenger S. Baumhoff J.-Y. Prieur J. Joffrin J.-P. Contour 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):177-182
We present measurements of the attenuation and phase velocity of surface acoustic waves in thin YBa2Cu3O films as a function of temperature, in magnetic fields up to 3.6 T applied parallel to the c-axis of the films. We have observed anomalies in both, the attenuation and the phase velocity in the vicinity of the superconducting
critical temperature which do not depend on the magnetic field. Possible origins of these anomalies, observed, to our knowledge,
for the first time in YBa2Cu3O thin films, are discussed and compared to bulk acoustic wave experiments. We present a kind of feedback technique for surface
acoustic waves which improves the sensitivity of this type of measurement. The actual sensitivity limits are mentioned.
Received: 7 August 1997 / Revised: 7 November 1997 / Accepted: 17 November 1997 相似文献
20.
S. Bellucci F. Carillo P. Onorato 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):509-515
We suggest a spin filter scheme using T-stub nanometric
crossjunctions patterned in two dimensional electron gases (2DEGs)
in the presence of spin orbit interaction (SOI).
We compare the effects of SOI arising from vertical confinement of charge carriers
in the well, Rashba or α-SOI, with SOI generated by lateral
confinement of the wire, β-SOI. We show that β coupling
can be more effective in generating a spin polarized current as
compared to α-SOI. We also compare the efficiency of the
T-stub filter with the one of the X shaped cross junction. 相似文献