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1.
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
2.
Y. Saito T. Inokuchi H. Sugiyama K. Inomata 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):463-469
We conducted a detailed study of hard axis magnetic field (Hhard)
dependence on current-induced magnetization switching (CIMS) in MgO-based
magnetic tunnel junctions (MTJs) with various junction sizes and various
uniaxial anisotropy fields. The decreases in critical current density
(Jc) and the intrinsic critical current density (Jc0) estimated from
the pulse duration dependence on Jc in CIMS are observed when applying
Hhard for all MTJs. The decrease in energy barrier of CIMS is also
observed except for the largest sample. These results indicate that the
reduction of Jc is attributable to both the increase of spin-transfer
efficiency and the decrease in energy barrier in the case of applying
Hhard. The Jc0 decreases with increase in the mutual angle between
the direction of magnetization and the easy axis (θf),
which is consistent with the theoretical prediction proposed by Slonczewski.
The degree of the reduction of Jc0 for the same value of Hhard
decreases with decreasing size of MTJs. This behavior is considered to be
related to not only decrease in θf due to the increase in
anisotropy field in MTJs, but also to the increase in the variance of the
initial angle of magnetization due to the thermally activated magnon
excitation. The stable switching endurance related to CIMS was observed in a
wide range of MTJ sizes when applying Hhard. Moreover, we proposed a new
architecture and a new switching method considering write disturbance. These
results would be useful for application to spin memory and other
spin-electronic devices. 相似文献
3.
K. P. McKenna G. J. Morgan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):451-456
A quantum equation of motion method is applied to simulate conduction electron spin-relaxation and transport in the presence
of the spin-orbit interaction and disorder. A spin-relaxation time of 25ps is calculated for Cu with a realistic low temperature
resistivity of 3.2 μΩ cm – corresponding to a spin-diffusion length of about 0.4 μm. Spin-relaxation in a finite nanocrystallite
of Cu is also simulated and a short spin-relaxation time (0.47 ps) is calculated for a crystallite with 7% surface atoms.
The spin-relaxation calculated for bulk Cu is in good agreement with experimental evidence, and the dramatic nanocrystallite
effect observed has important implications for nano-spintronic devices. 相似文献
4.
J.-P. Wang H. Meng 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):471-474
Spin torque transfer structures with new spin switching configurations are
proposed, fabricated and investigated in this paper. The non-uniform
current-induced magnetization switching is implemented based on both GMR and
MTJ nano devices. The proposed new spin transfer structure has a hybrid free
layer that consists of a layer with conductive channels (magnetic) and
non-conductive matrix (non-magnetic) and traditional free layer(s). Two
mechanisms, a higher local current density by nano-current-channels and a
non-uniform magnetization switching (reversal domain nucleation and growth)
by a magnetic nanocomposite structure, contribute in reducing the switching
current density. The critical switching current density for the new spin
transfer structure is reduced to one third of the typical value for the
normal structure. It can be expected to have one order of magnitude or more
reduction for the critical current density if the optimization of materials
and fabrication processes could be done further. Meanwhile, the thermal
stability of this new spin transfer structure is not degraded, which may
solve the long-standing scaling problem for magnetic random access memory
(MRAM). This spin transfer structure, with the proposed and demonstrated new
spin switching configurations, not only provides a solid approach for the
practical application of spin transfer devices but also forms a unique
platform for researchers to explore the non-uniform current-induced
switching process. 相似文献
5.
G. Michałek B. R. Bułka 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):411-419
Conductance and other physical quantities are calculated in double quantum dots (DQD) connected in series in the limit of
coherent tunnelling using a Green's function technique. The inter-dot Coulomb repulsion and the exchange interaction are studied
by means of the Kotliar and Ruckenstein slave-boson mean-field approach. The crossover from the atomic to the molecular limit
is analyzed in order to show how the conductance in the model depends on the competition between the level broadening (dot-lead
coupling) and the dot-dot transmission. The double Kondo effect
was found in the gate voltage characteristics of the conductance in the atomic limit. In the case, when each dot accommodates
one electron, the Kondo resonant states are formed between dots and their adjacent leads and transport is dominated by hopping
between these two resonances. In the molecular limit the conductance vanishes for sufficiently low gate voltages, which means
the Kondo effect disappeared. For small dot-lead coupling the transport characteristics are very sensitive on the influence
of the inter-dot Coulomb repulsion and the position of the local energy level. The
resonance region is widened with increase of the inter-dot Coulomb interactions while the exchange interaction has opposite
influence. 相似文献
6.
D. N. Son N. ArboledaJr W. A. Dino H. Kasai 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):27-35
We consider a two-terminal Aharonov-Bohm (AB) interferometer with a quantum dot inserted in one path of the AB ring.
We investigate the transport properties of this system in and out of the Kondo regime. We utilize perturbation theory to
calculate the electron self-energy of the quantum dot with respect to the intradot Coulomb interaction. We show the expression
of the Kondo temperature as a function of the AB phase together with its dependence on other characteristics such as the
linewidth of the ring and the finite Coulomb interaction and the energy levels of the quantum dot. The current oscillates
periodically as a function
of the AB phase. The amplitude of the current oscillation decreases with increasing Coulomb interaction. For a given temperature,
the electron transport through the AB interferometer
can be selected to be in or out of the Kondo regime by changing the magnetic flux threading perpendicular to the AB ring of
the system. 相似文献
7.
A. Cresti G. Grosso G. Pastori Parravicini 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):537-549
This paper addresses in a concise and rigorous way the basic tools for the study of local longitudinal and transverse microscopic
currents in two-dimensional devices. The emphasis is on the optimized use of the Keldysh nonequilibrium Green's function theory
together with the tight-binding representation of the electronic system. We elaborate general analytic expressions of current
profiles, useful for modeling and simulating the local site-to-site flow of carriers; furthermore, in broken time-reversal
symmetry, the formalism discerns unambiguously persistent and transport contributions to the bond currents. Our approach achieves
a workable theoretical imaging, resolved in space and energy, of the microscopic currents through mesoscopic devices. 相似文献
8.
H. Pan S.-Q. Duan L.-N. Zhao W.-D. Chu W. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):71-76
We theoretically study the spin pump effects of the rotating
magnetic field on the spin current through two coupled quantum dots.
Owing to the interdot coupling, two molecular states with different
bands can be formed, resulting asymmetric spin current peaks. The
possibility of manipulating the spin current is explored by tuning
the strength, the frequency, and the direction of the rotating
magnetic field. The number and location of the spin current peaks
can be controlled by making use of various tunings. Furthermore, the
normal 2π period of the spin current with respect to the
magnetic flux can be destroyed by the interdot coupling. 相似文献
9.
Transport through a double barrier in Large Radius Carbon Nanotubes
with a transverse magnetic field
S. Bellucci P. Onorato 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):469-476
We discuss the Luttinger Liquid behaviour of Large Radius Carbon Nanotube e.g. the Multi Wall ones (MWNT), under the action
of a transverse magnetic field B. Our results imply a reduction with B in the value of the bulk critical exponent, αbulk, for the tunneling density of states, which is in agreement with that observed in transport experiments. Then, the problem
of transport through a Quantum Dot formed by two intramolecular tunneling barriers along the MWNT, weakly coupled to Tomonaga-Luttinger
liquids is studied, including the
action of a strong transverse magnetic field B. We predict the presence of some peaks in the conductance G versus B, related
to the magnetic flux quantization in the ballistic regime, at a very low temperature T, and also at higher values of T, where
the Luttinger
behaviour dominates. The temperature dependence of the maximum Gmax of the conductance peak according to the Sequential Tunneling follows a power law, G ∝Tγe-1 with
γe linearly dependent on the critical exponent,
αend, strongly reduced by B. 相似文献
10.
C. C. Wang S. Jain A. O. Adeyeye 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(3):305-309
We investigate the magnetoresistance (MR) responses in a ferromagnetic
rectangular ring structure using a four-point probe technique. The measured
MR curves are strongly dependent on the electrical contact geometries used.
The associated MR characteristics are elucidated by a combination of
micromagnetic simulations and resistor-network based model, and the MR
contributions from different portions of the ring were studied
quantitatively. The systematic angular MR measured at the ring corner
further show that the locations of the domain wall nucleation are very
sensitive to the field alignment. 相似文献
11.
P. Schwab R. Raimondi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):5-8
We consider non-equilibrium transport in disordered conductors. We calculate the interaction correction to the current for
a short wire connected to electron reservoirs by resistive interfaces. In the absence of charging effects we find a universal
current-voltage-characteristics. The relevance of our calculation for existing experiments is discussed as well as the connection
with alternative theoretical approaches.
Received 2 September 2002 Published online 29 October 2002 相似文献
12.
A. Rycerz 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):291-296
We study quantum entanglement in a single-level quantum dot in the
linear-response regime.
The results show, that the maximal quantum value of the conductance
2e2/h not always match the maximal entanglement.
The pairwise entanglement between the quantum dot and the nearest atom of the
lead is also analyzed by utilizing the Wootters formula
for charge and spin degrees of freedom separately.
The coexistence of zero concurrence and the maximal conductance is observed
for low values of the dot-lead hybridization.
Moreover, the pairwise concurrence vanish simultaneously for charge and
spin degrees of freedom, when the Kondo resonance is present in the system.
The values of a Kondo temperature, corresponding to the zero-concurrence
boundary, are also provided. 相似文献
13.
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
14.
G.-Y. Sun C.-X. Wu Y. Chen Z.-L. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):459-464
Using the Keldysh nonequilibrium Green function method, we
theoretically investigate the electron transport properties of a
quantum dot coupled to two ferromagnetic electrodes, with
inelastic electron-phonon interaction and spin flip scattering
present in the quantum dot. It is found that the electron-phonon
interaction reduces the current, induces new satellite polaronic
peaks in the differential conductance spectrum, and at the same
time leads to oscillatory tunneling magnetoresistance effect. Spin
flip scattering suppresses the zero-bias conductance peak and
splits it into two, with different behaviors for parallel and
anti-parallel magnetic configuration of the two electrodes.
Consequently, a negative tunneling magnetoresistance effect may
occur in the resonant tunneling region, with increasing spin flip
scattering rate. 相似文献
15.
The theory of nanosize point contacts made of ferromagnetic metals is developed. A general quantum scattering theory is applied to calculate magnetoresistance of a nanocontact with a domain wall located in the constriction. The exact solution of the electron motion in a potential of the linear domain wall is used as a zero-order approximation. Spin-flip and spin-conserving quantized conductances of the nanocontact are calculated by the perturbation theory by the difference between the model and the Cabrera-Falicov potentials of the domain wall. It is explicitly shown that spin-flip conductance imposes natural limitation on magnetoresistance of the point contact, which otherwise diverges in the regime of complete spin-rectified conductance through the contact. 相似文献
16.
K. I. Mazzitello H. O. Mártin H. E. Roman 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(3):315-320
An array of silicon nanoclusters aimed at producing light emission upon injection
of electrons and holes from external sources is studied by Monte Carlo simulations.
The conditions for obtaining a significant charge accumulation in the emitting nanoclusters are investigated as a function
of array geometry and applied electric fields. It is found that if a stationary state, reached for an applied field F0, is suddenly perturbed by a field F1≫F0, a significant increase in electron-hole pairs population can be obtained with respect to the case of a single field of constant
intensity F1, leading to enhanced light emission when the conductivity of the array is above 6×10-10 [ Ω cm] -1. The excess population thus created gets fully recombined on the time scale of milliseconds, suggesting a device that can
produce enhanced light emission in the range of kilohertz. 相似文献
17.
We report a theoretical study of the equilibrium spin current flowing in a quantum dot system. Two electrodes are the two-dimensional electron gas with Rashba or Dresselhaus spin-orbital interaction. By using the Keldysh Green's function technique, we demonstrated that a nonzero spin current can flow in the system without bias. At the weak coupling between electrodes and the quantum dot, the spin current is approximately proportional to the cross product of two average pseudo-magnetizations in two electrodes, which agrees with the result of the linear response theory; whereas at the opposite case, the strong coupling between the quantum dot and electrodes can lead to a non-sinusoidal behavior of the equilibrium spin current. These behaviors of the equilibrium spin current are similar to the Josephson current. 相似文献
18.
19.
Correlated electron current and temperature dependence of the conductance of a quantum point contact
C. Sloggett A. I. Milstein O. P. Sushkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):427-432
We investigate finite temperature corrections to the Landauer formula
due to electron–electron interaction within the quantum point contact.
When the Fermi level is close to the barrier height, the conducting
wavefunctions become peaked on the barrier, enhancing the
electron–electron interaction. At the same time, away from the contact
the interaction is strongly suppressed by screening. To describe
electron transport we formulate and solve a kinetic equation for the
density matrix of electrons. The correction to the conductance G is
negative and strongly enhanced in the region 0.5 × 2e2/h ≤ G
≤ 1.0 × 2e2/h. Our results for conductance agree with the
so-called “0.7 structure” observed in experiments. 相似文献
20.
I. Vilfan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):277-284
The properties of
nanowires were investigated with
ab initio calculations based on the density-functional theory.
The molecules build weakly coupled one-dimensional chains, like
and Mo6S9-xIx, and the crystals are
strongly uniaxial in their mechanical and electronic properties.
The calculated moduli of elasticity and resilience along the chain axis are
c11 = 320 GPa and ER = 0.53 GPa, respectively.
The electronic band structure and optical conductivity indicate
that the
crystals are good quasi-one-dimensional conductors.
The frequency-dependent complex dielectric tensor ε, calculated
in the random-phase approximation, shows a strong Drude peak in
ε∥, i.e., for the electric field polarised parallel to
the chain axis, and several peaks related to interband transitions.
The electron energy loss spectrum is weakly anisotropic and has a strong peak
at the plasma frequency ħωp ≈20 eV.
The stability analysis shows that
is metastable against the
formation of the layered
. 相似文献