共查询到20条相似文献,搜索用时 11 毫秒
1.
M. Putti E. Galleani d'Agliano D. Marrè F. Napoli M. Tassisto P. Manfrinetti A. Palenzona C. Rizzuto S. Massidda 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):439-443
We report measurements of the resistivity, ρ, and the Seebeck coefficient, S
, of a MgB2 sintered sample, and compare S with theoretical calculations based on precise electronic structure calculations. ρ is fitted well by a generalized Bloch-Grüneisen equation with a Debye temperature Θ
R
of 1050 K. S is given by the sum of a diffusive and a phonon drag term and the behavior in the temperature region T
c
<
T
< 0.1Θ
R
follows the relationship AT+BT3. The phonon drag term indicates a strong electron-phonon interaction. The diffusive term, compared with calculations, suggests
that σ bands give the main contribution to the Seebeck effect.
Received 16 November 2001 and Received in final form 21 December 2001 相似文献
2.
R. De Luca A. Fedullo 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(1):59-66
The magnetic states of multi-junction superconducting quantum interference
device containing 2N identical conventional Josephson junctions are studied by
means of a perturbation analysis of the non-linear first-order ordinary
differential equations governing the dynamics of the Josephson junctions in
these devices. In the zero-voltage state, persistent currents are calculated
in terms of the externally applied magnetic flux Φex . The
resulting d.c. susceptibility curves show that paramagnetic and diamagnetic
states are present, depending on the value of Φex . The stability
of these states is qualitatively studied by means of the effective potential
notion for the system. 相似文献
3.
I. Pallecchi M. Monni C. Ferdeghini V. Ferrando M. Putti C. Tarantini E. Galleani D'Agliano 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):171-179
Recent experimental data of anisotropic magnetoresistivity measured in
MgB2 films have shown an intriguing behaviour: the angular dependence
of magnetoresistivity changes dramatically with temperature and disorder. In
order to explain such phenomenology, in this work, we extend our previous
analyses on multiband transverse magnetoresistivity in magnesium diboride,
by calculating its analytic expression, assuming a constant anisotropic
Fermi surface mass tensor. The calculation is done for arbitrary
orientation of the magnetic field with respect to the crystalline axes and
for the current density either perpendicular or parallel to the magnetic
field. This approach allows to extract quite univocally the values of the
scattering times in the σ- and π-bands by fitting experimental data with a
simple analytic expression.
We also extend the analysis to the magnetoresistivity of polycrystalline
samples, with an arbitrary angle between the current density and the
magnetic field, taking into account the anisotropy of each randomly oriented
grain.
Thereby, we propose magnetoresistivity as a very powerful characterization
tool to explore the effect of disorder by irradiation or selective doping as
well as of phonon scattering in each one of the two types of bands, in
single crystals and polycrystalline samples, which is a crucial issue in the
study of magnesium diboride. 相似文献
4.
S. Piano J. W.A. Robinson G. Burnell M. G. Blamire 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):123-126
The physics of the π phase shift in ferromagnetic
Josephson junctions may enable a range of applications for
spin-electronic devices and quantum computing. We investigate
transitions from “0” to “π” states in Nb/Fe/Nb Josephson
junctions by varying the Fe barrier thickness from 0.5 nm to 5.5 nm. From magnetic measurements we estimate for Fe a magnetic
dead
layer of about 1.1 nm. By fitting the characteristic voltage
oscillations with existing theoretical models we extrapolate an
exchange energy of 256 meV, a Fermi velocity of 1.98 ×105
m/s and an electron mean free path of 6.2 nm, in agreement with
other reported values. From the temperature dependence of the
ICRN product we show that its decay rate exhibits a nonmonotonic
oscillatory behavior with the Fe barrier thickness. 相似文献
5.
M. Bonura A. Agliolo Gallitto M. Li Vigni C. Ferdeghini C. Tarantini 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):165-177
We report on the microwave surface resistance of two
polycrystalline Mg11 B2 samples; one consists of
pristine material, the other has been irradiated at very high neutron
fluence. It has already been reported that in the strongly irradiated
sample the two gaps merge into a single value. The mw surface resistance
has been measured in the linear regime as a function of the temperature and the DC magnetic
field, at increasing and decreasing fields. The results obtained in the
strongly irradiated sample are quite well justified in the framework of a
generalized Coffey and Clem model, in which we take into account the field
distribution inside the sample due to the critical state. The results
obtained in the pristine sample show several anomalies, especially at low
temperatures, which cannot be justified in the framework of standard
models for the fluxon dynamics. Only at temperatures near Tc and for
magnetic fields greater than 0.5Hc2(T) the experimental data can quantitatively be
accounted for by the Coffey and Clem model, provided that the
upper-critical-field anisotropy is taken into due account. 相似文献
6.
B. Gorshunov C.A. Kuntscher P. Haas M. Dressel F.P. Mena A.B. Kuz'menko D. van der Marel T. Muranaka J. Akimitsu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):159-161
Far-infrared reflectivity studies on the polycrystalline intermetallic compound MgB2 with a superconducting transition temperature T
c
= 39 K were performed at temperatures 20 K to 300 K. We observe a significant raise of the superconducting-to-normal state reflectivity
ratio below 70
cm
-1
, with a maximum at about 25-30
cm
-1
, which gives a lower estimate of the superconducting gap of 2Δ(0)
≈ 3-4 meV.
Received 7 March 2001 and Received in final form 18 April 2001 相似文献
7.
A. Agliolo Gallitto G. Bonsignore G. Giunchi M. Li Vigni 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):537-542
We discuss the microwave second-harmonic generation in
high-density bulk MgB2, prepared by the reactive liquid Mg
infiltration technology. The intensity of the harmonic signal has
been investigated as a function of temperature and amplitudes of
the DC and microwave magnetic fields. The results are discussed in
the framework of a phenomenological theory, based on the two-fluid
model, which assumes that both the microwave and static magnetic
fields, penetrating in the surface layers of the sample, weakly
perturb the partial concentrations of the normal and
superconducting fluids. We show that, in order to account for the
experimental results, it is essential to suppose that in MgB2
the densities of the normal and condensed fluids linearly depend
on the temperature. 相似文献
8.
V. P.S. Awana A. Vajpayee M. Mudgel V. Ganesan A. M. Awasthi G. L. Bhalla H. Kishan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(3):281-294
We report synthesis, structure/micro-structure, resistivity under magnetic
field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity
κ(T), and magnetization of ambient pressure argon annealed
polycrystalline bulk samples of MgB2, processed under identical
conditions. The compound crystallizes in hexagonal structure with space
group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs
showing various types of defect features along with the presence of 3–4 nm
thick amorphous layers forming the grain boundaries of otherwise crystalline
MgB2. Raman spectra of the compound at room temperature exhibited
characteristic phonon peak at 600 cm-1. Superconductivity is observed
at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power
S(T), and thermal conductivity κ(T) measurements. The power law fitting
of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is
found consistent with the theoretical fitting of S(T), exhibiting Θ
D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal
conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was
missing in some earlier reports. Critical current density (Jc) of up to
105 A/cm2 in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K
is seen from magnetization measurements. The irreversibility field, defined
as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe
at 4, 10 and 20 K respectively. The superconducting performance parameters
viz. irreversibility field (Hirr) and critical current density
Jc(H) of the studied MgB2 are improved profoundly with addition of
nano-SiC and nano-diamond. The physical property parameters measured for
polycrystalline MgB2 are compared with earlier reports and a
consolidated insight of various physical properties is presented. 相似文献
9.
J.J. Betouras V.A. Ivanov F.M. Peeters 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):349-354
We present a model of pressure effects of a two-band superconductor based on a Ginzburg-Landau free energy with two order
parameters. The parameters of the theory are pressure as well as temperature dependent. New pressure effects emerge as a result
of the competition between the two bands. The theory then is applied to MgB2. We identify two possible scenaria regarding the fate of the two σ subbands under pressure, depending on whether or not both subbands are above the Fermi energy at ambient pressure. The splitting
of the two subbands is probably caused by the E2g distortion. If only one subband is above the Fermi energy at ambient pressure (scenario I), application of pressure diminishes
the splitting and it is possible that the lower subband participates in the superconductivity. The corresponding crossover
pressure and Gr neisen parameter are estimated. In the second scenario both bands start above the Fermi energy and they move below it, either
by pressure or via the substitution of Mg by Al. In both scenaria, the possibility of electronical topological transition is emphasized. Experimental
signatures of both scenaria are presented and existing experiments are discussed in the light of the different physical pictures.
Received 3 September 2002 / Received in final form 16 December 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: joseph.betouras@ua.ac.be
RID="b"
ID="b"On leave from N.S. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, 31 Leninskii
prospekt, 117915, Moscow, Russia 相似文献
10.
R. De Luca A. Fedullo V. A. Gasanenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):461-467
The dynamical properties of symmetric quantum interferometers with equal
junctions of negligible capacitance have been studied by means of
perturbation analysis in the limit of small values of the parameter β. In
this limit, two characteristic time constants arise. These quantities may be
linked to two different dynamical processes in the system: the first is
related to the time evolution of the average superconducting phase
difference across the two junctions; the second defines the time scale for
flux motion. The response of the system to constant and time-dependent
externally applied magnetic fields is considered and a general perturbed
solution for the average superconducting phase difference and the fluxon
number variable is derived to first order in β. 相似文献
11.
C. Paduani C. A. Kuhnen 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):331-336
Band structure and Fermi surfaces of the A3B compounds V3Co,
V3Rh, V3Ir and V3Os are calculated in FP-LAPW calculations.
From V3Co to the V3Os compound one observes a decrease of the
overlap for d-states from both V and B atoms; the center of
gravity of the d-band for V moves upwards, while for the B-atom
it moves toward lower energies. Hence, despite the band widening,
a weakening of interactions takes place throughout this series,
which leads to a lattice expansion as experimentally observed. The
bonding mechanism in these compounds is found to be dominated by
the lower energy d-states. Comparatively, the DOS at EF does
not change appreciably between these compounds, except for V3Os,
where a sharp peak is observed at EF. This feature leads to the
highest electronic heat-capacity coefficient γ (2.31
) in this compound, which otherwise
possesses the smallest Bulk modulus (209.05 GPa). In V3Os, for
whom no report has been found, a stronger admixture between
p-states from both metals near EF is observed, and the Os
d-states form a common d-band with the V d-states between
0.4–0.6 Ry. A stronger s–s hybridization is observed for V3Co,
which is in the source of the fact that this compound has an
anomalously large quadrupole interaction and exhibits a positive
Knight shift. 相似文献
12.
I. Shigeta Y. Tanaka F. Ichikawa Y. Asano 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):141-149
We propose a new approach of smearing origins of a zero-bias
conductance peak (ZBCP) in high-Tc superconductor tunnel
junctions through the analysis based on the circuit theory for a
d-wave pairing symmetry.
The circuit theory has been recently developed from conventional
superconductors to unconventional superconductors.
The ZBCP frequently appears in line shapes for this theory, in which the
total resistance was constructed by taking account of the effects
between a d-wave superconductor and a diffusive normal metal (DN) at a
junction interface, including the midgap Andreev resonant states (MARS),
the coherent Andreev reflection (CAR) and the proximity effect.
Therefore, we have analyzed experimental spectra with the ZBCP of
Ag-SiO-Bi2Sr2CaCu2O8+δ (Bi-2212) planar tunnel
junctions for the {110}-oriented direction by using a simplified
formula of the circuit theory for d-wave superconductors.
The fitting results reveal that the spectral features of the ZBCP are
well explained by the circuit theory not only excluding the Dynes's
broadening factor but also considering only the MARS and the DN
resistance.
Thus, the ZBCP behaviors are understood to be consistent with those of
recent studies on the circuit theory extended to the systems containing
d-wave superconductor tunnel junctions. 相似文献
13.
C. Benjamin T. Jonckheere A. Zazunov T. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):279-289
We consider a model for a single molecule with a large frozen spin
sandwiched in between two BCS superconductors at equilibrium, and
show that this system has a π junction behavior at low
temperature. The π shift can be reversed by varying the other
parameters of the system, e.g., temperature or the position of the
quantum dot level, implying a controllable π junction with
novel application as a Josephson current switch. We show that the mechanism
leading to the π shift can be explained simply in terms of the contributions
of the Andreev bound states and of the continuum of states above the superconducting gap.
The free energy for certain configuration of parameters shows a
bistable nature, which is a necessary pre-condition for
achievement of a qubit. 相似文献
14.
G. Campi E. Cappelluti Th. Proffen X. Qiu E. S. Bozin S. J.L. Billinge S. Agrestini N. L. Saini A. Bianconi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(1):15-21
We have studied temperature evolution of the local as well as the
average crystal structure of MgB2 using real-space atomic pair
distribution function (PDF) measured by high resolution neutron powder
diffraction in a wide temperature range of T=10–600 K. We find small
positive correlation factors for the B–B and B–Mg pairs, determined by
mean-square displacements (MSD) and the mean-square relative
displacements (MSRD). We analyze the PDF using both Einstein and
force constant models finding a good agreement between the
experimental data and the two models. This indicates that B and Mg
atomic correlations are not sensitive to the details of phonon
dispersion. 相似文献
15.
We theoretically calculate the Josephson current for two
superconductor/ferromagnetic semiconductor (SC/FS) bilayers
separated by a semiconductor (SM) layer. It is found that the
critical Josephson current IC in the junction is strongly
determined by not only the relative orientations of the effective
exchange field
of the two bilayers and scattering
potential strengths at the interfaces but also the kinds of holes
(the heavy or light) in the two FS layers. Furthermore, a robust
approach to measuring the spin polarization P for the heavy and
light holes is presented. 相似文献
16.
E. Govea-Alcaide I. García-Fornaris P. Muné R. F. Jardim 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):373-378
Measurements of the electrical resistivity as a function
of temperature, ρ(T), for different values of applied
magnetic field, Ba (0 ≤ Ba ≤ 50 mT), were performed in
polycrystalline samples of Bi1.65Pb0.35Sr2Ca2
Cu3O10+δ subjected to different uniaxial compacting
pressure (UCP). We have found appreciable differences in the grain
orientation between samples by using X-ray diffractometry. From
the X-ray diffraction patterns performed, in powder and pellet
samples, we have estimated the Lotgering factor along the (00l)
direction, F(00l). The results indicate that F(00l)
increases ~23% with increasing UCP suggesting that grains
of these samples are preferentially aligned along the c-axis,
which is parallel to the compacting direction. The resistive
transition of the samples have been interpreted in terms of the
thermally activated flux-creep model. In addition, the effective
intergranular pinning energy, U0, have been determined for
different applied magnetic field. The magnetic field dependence of
U0, for Ba > 8 mT, was found to follow a H- α
dependence with α = 0.5 for all samples. The analysis of the
experimental data strongly suggested that increasing UCP results
in appreciable changes in both the grain alignment and the grain
connectivity of the samples. We have successfully interpreted the
data by considering the existence of three different
superconducting levels within the samples: the superconducting
grains, the weak-links, and the superconducting clusters. 相似文献
17.
A. Vecchione D. Zola G. Carapella M. Gombos S. Pace G. Costabile C. Noce 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):151-157
Low frequency transport measurements are performed on GdSr2RuCu2O8 pellets. The observed current-voltage curves are qualitatively explained in the framework of a simple phenomenological model
accounting for coexistence in the sample of ferromagnetism and superconductivity. A Curie temperature T
cM
= 133 K and a superconducting critical temperature T
cS
= 18 K, with an onset temperature T
cO
= 33 K, are extracted from the analysis of the current-voltage curves.
Received 18 September 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: canio@sa.infn.it 相似文献
18.
Y. L. Feng K. Shen 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(1):105-110
We study chaos synchronization in two resistive-capacitive-inductive-shunted (RCL-shunted) Josephson junctions
(RCLSJJs) by using a common chaos driving. The numerical
simulations confirm that the synchronization of two RCLSJJs can be achieved
with a suitable driving intensity when the maximum condition Lyapunov
exponent (MCLE) is negative. 相似文献
19.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
20.
S. C. Li W. S. Duan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):485-491
We show that there is a link between the Kuramoto paradigm and another system of synchronized oscillators, namely an electrical
power distribution grid of generators and consumers. The purpose of this work is to show both the formal analogy and some
practical consequences. The mapping can be made quantitative, and under some necessary approximations a class of Kuramoto-like
models, those with bimodal distribution of the frequencies, is most appropriate for the power-grid. In fact in the power-grid
there are two kinds of oscillators: the “sources" delivering power to the “consumers". 相似文献