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1.
Z.-Y. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):65-69
Along the lines of Blonder, Tinkham and Klapwijk, we investigate
the charge transport through ferromagnet/two-dimensional
electronic gas/d-wave superconductor (F/2DEG/S) junctions in the
presence of Rashba spin-orbit (SO) coupling and focus our
attention on the interplay between spin polarization and spin
precession. At zero spin polarization, the spin-mixing scattering
resulted from Rashba SO coupling decreases the zero-bias
conductance peak. Under spin polarization, spin precession
introduces novel Andreev reflection, which competes with the
effect of spin-mixing scattering. If the F layer is a half metal,
the later effect is overwhelmed by that of novel Andreev
reflection. As a result, the zero-bias conductance dip caused by
spin polarization is enhanced, and at strong Rashba SO coupling, a
split zero-bias peak is found in the gap. In an intermediate
region where the two effects are comparable with each other, the
zero-bias conductance shows a reentrant behavior as a function of
Rashba SO coupling. 相似文献
2.
Z.?Radovi? V.?Paltoglou N.?Lazarides N.?Flytzanis 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(2):229-236
We study the Josephson effect in ballistic double-barrier SINIS planar junctions, consisting of bulk superconductors (S),
a clean normal metal or semiconductor (N), and insulating interfaces (I) modeled as a δ-function potential-energy barriers.
We solve the scattering problem based on the Bogoliubov-de Gennes equations and derive a general expression for the dc Josephson
current, valid for arbitrary interfacial transparency, the Fermi wave vectors mismatch, and for different effective band masses.
The effect of transmission resonances on the Josephson current and on the normal conductance is analyzed for short junctions.
Curvature of the temperature dependence of the critical Josephson current is related to the presence of resonances at the
Fermi level and to the interfacial transparency. For thin semiconductor layers with negative effective masses of the carriers,
finite interfacial transparency and large Fermi wave vectors mismatch we find that an unusual and significant enhancement
of both the normal conductance and the critical Josephson current occurs at low temperatures due to the presence of an evanescent
mode localized at interfaces. 相似文献
3.
Z. P. Niu Z. M. Zheng D. Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):281-287
Four-component Bogoliubov-de Gennes equations are applied to study
tunneling conductance spectra of ferromagnet/ferromagnet/d-wave
superconductor (F1/F2/d-wave S) tunnel junctions and to find
out signs of spin-triplet pairing correlations induced in the
proximity structure. The pairing correlations with equal spins
arises from the novel Andreev reflection (AR), which requires at
least three factors: the usual AR at the F2/S interface, spin
flip in the F2 layer, and superconducting coherence kept up in
the F2 layer. Effects of angle α between magnetizations of
the two F layers, polarizations of the F1 and F2 layers, the
thickness of the F2 layer, and the orientation of the d-wave S crystal on the tunneling conductance are investigated. A conversion
from a zero-bias conductance dip at α = 0 to a zero-bias
conductance peak at a certain value of α can be seen as a
sign of generated spin-triplet correlations. 相似文献
4.
Considering the Rashba spin-orbit interaction in the semiconductor, we study theoretically the spin-polarized transport in a two-dimensional ferromagnetic semiconductor double tunnel junctions by a quantum-mechanical approach. It is found that the transmission coefficient shows typical resonant transmission properties and the Rashba spin-orbit coupling has great different influences on the transmission coefficients of electrons with spin-up and down and tunnelling magnetoresistance (TMR). More importantly, the TMR is significantly enhanced by increasing the spin-orbit coupling, which is very useful for the designing of magnetic digital and memory sensor. 相似文献
5.
Z.Y. Zeng Baowen Li F. Claro 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):401-405
A unified theory for the current through a mesoscopic region of interacting electrons connected to two leads which can be
either ferromagnet or superconductor is presented, yielding Meir-Wingreen-type formulas when applied to specific circumstances.
In such a formulation, the requirement of gauge invariance is satisfied automatically. Moreover, one can judge unambiguously
what quantities can be measured in the transport experiment.
Received 22 August 2002 / Received in final form 14 February 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: phyzengz@nus.edu.sg 相似文献
6.
H.-K. Zhao J. Wang Q. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):425-433
We have investigated the mesoscopic transport through the system
with a quantum dot (QD) side-coupled to a toroidal carbon nanotube
(TCN) in the presence of spin-flip effect. The coupled QD
contributes to the mesoscopic transport significantly through
adjusting the gate voltage and Zeeman field applied to the QD.
The compound TCN-QD microstructure is related to the separate
subsystems, the applied external magnetic fields, as well as the
combination of subsystems. The spin current component Izs is
independent on time, while the spin current components Ixs and
Iys evolve with time sinusoidally. The rotating magnetic field
induces novel levels due to the spin splitting and photon
absorption procedures. The suppression and enhancement of resonant
peaks, and semiconductor-metal phase transition are observed by
studying the differential conductance through tuning the
source-drain bias and photon energy. The magnetic flux induces
Aharonov-Bohm oscillation, and it controls the tunnelling behavior
due to adjusting the flux. The Fano type of multi-resonant
behaviors are displayed in the conductance structures by
adjusting the gate voltage Vg and the Zeeman field
applied to the QD. 相似文献
7.
A. Saffarzadeh M. Ghorbani Asl 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):239-244
Using the tight-binding approximation and the nonequilibrium Green’s function approach, we investigate the coherent spin-dependent
transport in planar magnetic junctions consisting of two ferromagnetic (FM) electrodes separated by a graphene flake (GF)
with zigzag or armchair interfaces. It is found that the electron conduction strongly depends on the geometry of contact between
the GF and the FM electrodes. In the case of zigzag interfaces, the junction demonstrates a spin-valve effect with high magnetoresistance
(MR) ratios and shows negative differential resistance features for a single spin channel at positive gate voltage. In the
case of armchair interfaces, the current-voltage characteristics behave linearly at low bias voltages and hence, both spin
channels are in on state with low MR ratios. 相似文献
8.
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
9.
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
10.
B. Frank K.Y. Platov W. Krech 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):187-192
The synchronization properties of a simple two-dimensional Josephson array consisting of two coupled SQUID cells are studied
within the Werthamer as well as the RCSJ model. Special emphasis is placed on the role of inductances arranged perpendicular
and parallel to the current bias direction for the phase locking behavior. The general behavior within the Werthamer model
is found to be similar to that within the RCSJ model. However, there are quantitative differences, e.g. an enhanced phase shift between the voltage oscillations within one cell and a shift of the parameter range for the in-phase
regime between different cells towards lower values of the McCumber parameter in the Werthamer model.
Received: 23 March 1998 / Revised: 3 June 1998 / Accepted: 9 June 1998 相似文献
11.
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
12.
G.P. Pepe G. Peluso R. Scaldaferri L. Parlato C. Granata E. Esposito M. Russo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):421-425
A new fabrication process for three-terminal superconducting devices consisting of two Josephson junctions in a stacked configuration
is reported. The process is based on the deposition of the whole Nb/AlxOy/Nb-Al/AlxOy/Nb multilayer on a Si crystalline wafer without any vacuum breaking. Lift-off techniques, anodization processes and a SiO
film deposition have been adopted for patterning and insulating the two tunnel stacked junctions. Devices have been characterized
in terms of current-voltage (I-V) curves and Josephson critical current vs. the externally applied magnetic field. They show high quality factors (V
m values up to 65 mV at 4.2 K), and good current uniformity.
Received 5 June 2001 相似文献
13.
R. Migliore A. Messina A. Napoli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):111-115
A simple way to acquire information on the mean values of the phase operators sinϕ and cosϕ of an ultrasmall Josephson junction
prepared in an arbitrary pure or not state is reported. Our proposal exploits the recently predicted occurrence of current
spikes in the I-V characteristic of a mesojunction irradiated by a quantum single-mode low-intensity coherent electromagnetic field. A necessary
condition for the validity of our treatment is presented and discussed.
Received 11 April 2001 相似文献
14.
The collective resonant photoresponse in Si/SiGe structures with a 2DEG under microwave radiation is reported for the first time. The application of microwave radiation of various frequencies results in resonant photoconductivity at magnetic field values that are systematically lower than expected for the cyclotron resonance (CR) in an infinitely large two-dimensional electron system. The analysis of the data shows that the observed microwave radiation induced response is dominated by plasmon excitations. 相似文献
15.
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
16.
R. Migliore A. Messina A. Napoli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):585-588
We prove that a mesoscopic Josephson junction, irradiated with a quantum superposition of two -out of phase optical coherent states, exhibits an experimentally observable sensitivity to the quantum coherences of the
field state.
Received 1 June 1999 and Received in final form 30 July 1999 相似文献
17.
F. Liang Y. H. Yang J. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):337-341
We propose an electrical scheme for the generation of a pure spin current without a charge current in a two-terminal device,
which
consists of a scattering region of a two-dimensional electron gas
(2DEG) with Rashba (R) and/or Dresselhaus (S) spin-orbit interaction (SOI)
and two normal leads. The SOI is modulated by a time-dependent gate
voltage to pump a spin current. Based on a tight-binding model and
the Keldysh Green’s function technique, we obtain the analytical
expression of the spin current. It is shown that a pure spin current
can be pumped out, and its magnitude could be modulated by
device parameters such as the oscillating frequency of the SOI, as
well as the SOI strength. Moreover, the spin polarisation direction of
the spin current could also be tuned by the strength ratio between
RSOI and DSOI. Our proposal provides not only a fully electrical means
to generate a pure spin current but also a way to control the spin
polarisation direction of the generated spin current. 相似文献
18.
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
19.
C. Hoffmann F. Lefloch M. Sanquer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):629-633
We studied electronic relaxation in long diffusive superconductor/normal metal/superconductor (S/N/S) junctions by means of
current noise and transport measurements down to very low temperature (100mK). Samples with normal metal lengths of 4, 10
and 60μm have been investigated. In all samples the shot noise increases very rapidly with the voltage. This is interpreted
in terms of enhanced heating of the electron gas confined between the two S/N interfaces. Experimental results are analyzed
quantitatively taking into account electron-phonon interaction and heat transfer through the S/N interfaces. Transport measurements
reveal that in all samples the two S/N interfaces are connected incoherently, as shown by the reentrance of the resistance
at low temperature. The complementarity of noise and transport measurements allows us to show that the energy dependence of
the reentrance at low voltage is essentially due to the increasing effective temperature of the quasiparticles in the normal
metal.
Received 5 February 2002 / Received in final form 6 September 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: hoffmann@drfmc.ceng.cea.fr 相似文献
20.
M. Pletyukhov S. Konschuh 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):29-43
We analytically evaluate charge and spin density response functions of the
clean two-dimensional electron gas with Rashba spin-orbit coupling at finite
momenta and frequencies. On the basis of our exact expressions we discuss the
accuracy of the long-wavelength and the quasiclassical approximations. We also
derive the static limit of spin susceptibilities and demonstrate,
in particular, how the Kohn-like anomalies in their derivatives are related
to the spin-orbit modification of the Ruderman-Kittel-Kasuya-Yosida
interaction. Taking into account screening and exchange effects of the Coulomb
interaction, we describe the collective charge and spin density excitation
modes which appear to be coupled due to nonvanishing spin-charge response
function. 相似文献