共查询到20条相似文献,搜索用时 218 毫秒
1.
Q. Chen H. -K. Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):237-248
We have investigated the spectral density of shot noise for an ultra-small quantum dot(QD) system in the Coulomb blockade
regime when irradiated with microwave fields (MWFs) by employing a nonequilibrium Green’s function technique. The shot noise
is sensitive to Coulomb interaction, and the photon-assisted Coulomb blockade behaviour strongly modifies the mesoscopic transport.
We have calculated the first and second derivatives of shot noise in the strong and weak coupling regimes to compare the theoretical
results with existing experimental results. In the strong coupling regime, the first and second derivatives of shot noise
display Fano type peak-valley structures around the charging channel 2E
c
due to Coulomb interaction. When the magnitudes of the MWFs are sufficiently large, the system displays channel blockade
due to photon irradiation. The photon-assisted and Coulomb blockade steps in the noise — as well as the resonant behaviour
in the differential noise — are smeared by increasing temperature. The Coulomb interaction suppresses the shot noise, but
the ac fields can either suppress the shot noise(balanced case) or enhance the shot noise(unbalanced case). The suppression
of shot noise caused by ac fields in the balanced case is greater than that caused by Coulomb interaction in our system. Super-Poissonian
shot noise may be induced due to the compound effects of strong Coulomb interaction and photon absorption-emission processes. 相似文献
2.
He Gao 《Physics letters. A》2010,374(5):770-777
The commensurate photon-irradiated mesoscopic transport in a strongly correlated quantum dot (QD) embedded Aharonov-Bohm (AB) interferometer has been investigated. We focus our investigation on the dynamic Kondo and Fano cooperated effect affected by the double commensurate MWFs with q=ω2/ω1 being an arbitrary integer, where ω1 and ω2 are the two frequencies of the fields. The general tunneling current formula is derived by employing the nonequilibrium Green's function technique, and the different photon absorption and emission processes induced nonlinear properties have been studied to compare with the single-field system where q=0. Our numerical calculations are performed for the special cases with two commensurate fields possessing q=1,2. The Kondo peak can be suppressed to be a Kondo valley for the case where the commensurate number q=1, and the Fano asymmetric structure exhibits in the differential conductance quite evidently. Different commensurate number q contributes different photon absorption and emission effects. However, the conductance for the case of q=2 possesses more peaks and heavier asymmetric structure than the situations of q=0,1. The enhancement of satellite peaks behaves quite differently for the two cases with q=1, and q=2. The asymmetric peak-valley structure is adjusted by the gate voltage, commensurate MWFs, AB flux, source-drain bias, and non-resonant tunneling strength to form novel Fano and Kondo resonant tunneling. 相似文献
3.
H.-K. Zhao Q. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):419-427
We have investigated the spectral density of shot noise for the
system of a quantum dot (QD) coupled to two single-wall carbon
nanotube terminals irradiated with a microwave field on the QD. The
terminal features are involved in the shot noise through modifying
the self-energy of QD. The contributions of carbon nanotube
terminals to the shot noise exhibit obvious behaviors. The novel
side peaks are associated with the photon absorption and emission
procedure accompanying the suppression of shot noise. The shot noise
in balanced absorption belongs to sub-Poissonian, and it is
symmetric with respect to the gate voltage. The differential shot
noise displays intimate relation with the nature of carbon nanotubes
and the applied microwave field. It exhibits asymmetric behavior
for the unbalanced absorption case versus gate voltage. The Fano
factor of the system exhibits the deviation of shot noise from the
Schottky formula, and the structures of terminals obviously
contribute to it. The super-Poissonian and sub-Poissonian shot noise
can be achieved in the unbalanced absorption in different regime of
source-drain bias. 相似文献
4.
V E Kravtsov 《Pramana》2002,58(2):183-193
It is shown that the variance of the linear dc conductance fluctuations in an open quantum dot under high-frequency ac pumping
depends significantly on the spectral content of the ac field. For a sufficiently strong ac field the dc conductance fluctuations
are much stronger for the periodic pumping than in the case of the noise ac field of the same intensity. The reduction factor
r in a static magnetic field takes the universal value of 2 only for the white-noise pumping. In general r may deviate from 2 thus signalling on the time-reversal breaking by the ac field. For the bi-harmonic ac field of the form
A(t) = A
0[cos(ω
1
t) − cos(ω
2
t)] we predict the enchancement of effects of T-symmetry breaking at commensurate frequencies ω
2/ω
1 = P/Q. In the high-temperature limit there is also the parity effect; the enchancement is only present if either P or Q is even. 相似文献
5.
We have investigated the shot noises of charge and spin current by considering the spin polarized electron tunneling through
a ferromagnet-quantum-dot-ferromagnet system. We have derived the spin polarized current noise matrix, from which we can derive
general expressions of shot noises associated with charge and spin currents. The spin and charge currents are intimately related
to the polarization angles, and they behave quite differently from each other. The shot noise of charge current is symmetric
about the gate voltage whose structure is modified by the Zeeman field considerably. There exists oscillations in spin current
shot noise in the absence of source-drain bias at zero temperature, and it is asymmetric in the positive and negative regimes
of sourcedrain voltage. The shot noise of spin current behaves quite differently from the shot noise of charge current, since
the spin current components I
x
s
, I
y
s
oscillate sinusoidally with the frequency ωγ in the γth lead, while the I
z
s
component of spin current is independent of time.
相似文献
6.
Molin Liu Jianbo Lu Yuanxing Gui 《The European Physical Journal C - Particles and Fields》2009,59(1):107-116
On the basis of the 4D momentum, the influence of quintessence on the gravitational frequency shift and the deflection of
light are examined in modified Schwarzschild space. We find that the frequency of a photon depends on the state parameter
of the quintessence w
q: the frequency increases for −1<w
q<−1/3 and decreases for −1/3<w
q<0. Meanwhile, we adopt an integral power number a (a=3ω
q+2) to solve the orbital equation of photon. The photon’s potentials become higher with the decrease of ω
q. The behavior of the bending light sensitively depends on the state parameter ω
q. In particular, for the case of ω
q=−1, there is no influence on the deflection of light by quintessence. Furthermore, according to the H-masers of the GP-A
redshift experiment and long-baseline interferometry, the constraints on the quintessence field in the solar system are presented
here. 相似文献
7.
H.-K. Zhao L.-L. Zhao J. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):441-451
We have investigated the shot noise in the mesoscopic system
composed of a quantum dot (QD) coupled to ferromagnetic terminals
under the perturbation of ac fields. The shot noise has been derived
using the nonequilibrium Green's function (NGF) technique to
describe the spin polarization effect along with photon absorption
and emission processes in the Coulomb blockade regime. We have
examined the influence of spin polarization on the shot noise under
the perturbation of ac fields in the nonadiabatic regime.
The Coulomb blockade effect results
in the modification of shot noise compared with the noninteracting
case. The spin orientation contributes a spin valve effect for
controlling electron tunnelling through this QD, and different
resonant forms appear around the Coulomb blockade channel. The
photon-assisted spin-splitting and spin-polarization effect
contributes a photon-assisted spin valve to adjust the electron
tunnelling current and shot noise. The spin-polarization effect
varies the value of the Fano factor. However, it does not change
the noise type from sub-Poissonian to super-Poissonian. 相似文献
8.
Xin-Hai Liu Xue-Hua Wang Ben-Yuan Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):37-41
The collective charge density excitations in asymmetric double-quantum-well (DQW) structures with different tunneling strengths
are systematically studied. In particular, the damping properties of the plasmon modes in various tunneling strengths are
investigated in detail. It is shown that plasmon modes in asymmetric DQW structures are quite different from those in symmetric
DQW systems. In weak tunneling regime, an intra-subband mode ω
- with an acoustic-like dispersion relation which is damped in symmetric DQW structures arises and coexists with the optical-like
mode ω
+ while the inter-subband mode ω
10 is highly damped. With the tunneling strength being increased, the ω
10 branch gradually becomes undamped and emerges out of the (1-0) single-particle continuum, whereas the ω
- branch gradually approaches the (0-0) single-particle continuum. In intermediate coupling regime, these three branches of
modes coexist undamped. In strong tunneling regime, ω
- enters the (0-0) single-particle continuum and becomes damped. Consequently, only the ω
+ and ω
10 modes exist in this regime.
Received 10 July 2001 and Received in final form 17 September 2001 相似文献
9.
Zhao Hong-kang 《Frontiers of Physics in China》2007,2(1):55-62
Current noise exists in circuits and electronic devices generally, and it exhibits specific features as the system reaches
nanometer size. The noise in the nano-system where external ac fields are applied plays an important role, since the properties
of the fields and the nano-system together govern the resulting noise. In this paper, we present the derivation of shot noise
by employing the non-equilibrium Green’s function technique. The more general formulas for the current correlation and noise
spectral density are given. The system is composed of a central nanosystem coupled to electrodes, and the obtained noise formulas
are related to the Green’s functions of detailed central regime and the terminals. As an example, we have performed the numerical
calculation on a system with a toroidal carbon nanotube coupled to normal metal leads. The noise and Fano factor show intimate
relation with the structure of the system and ac fields. The Aharonov-Bohm-like behaviors on the shot noise spectral density
and Fano factor are observed to exhibit oscillation structures with period of quantum flux.
相似文献
10.
A theory of the shift current induced by direct two-photon and indirect one-photon absorption is developed for noncentrosymmetric
crystals. A formula is derived for the microscopic shifts of Bloch electrons induced by two-quantum processes. It is shown
that the ratio of the two-photon photocurrent at the photon frequency ω to the photocurrent induced by direct one-photon transitions
at the photon frequency 2ω, as compared to the corresponding absorption-rate ratio, contains a large factor {ie152-1}ω/(2{ie152-2}ω
− E
g), where E
g is the bandgap; i.e., these photocurrent can be comparable in order of magnitude. For crystals of T
d
symmetry, the photocurrents induced by one- and two-photon absorption are compared in terms of polarization dependence. 相似文献
11.
The shot noise of a hybrid triple-quantum-dot (TQD) interferometer has been investigated by employing the nonequilibrium Green's function method, and the general shot noise formula has been derived. The oscillation behaviors of transmission coefficients and shot noise versus the Aharonov–Bohm phase ? exhibit asymmetric Fano resonance structure and blockade effect. Sub-Poissonian and super-Poissonian behaviors of shot noise appear in different regimes of terminal bias eVγ contributed by the Andreev reflection, and correlation of Andreev tunneling with the normal electron transport. The inverse resonance and resonance structures emerge in the shot noise and Fano factor with respect to one of the gate voltages in different regimes of eVγ. The asymmetric structure can be enhanced by modifying the energy levels and gate biases of the TQD. The self-correlation and cross-correlation of current components contribute to the enhancement and suppression of shot noise. 相似文献
12.
P. Paasche C. Angelescu S. Ananthamurthy D. Biswas T. Valenzuela G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):183-188
We have measured the storage instabilities of electrons in a Penning trap at low magnetic fields. These measurements are carried
out as a function of the trapping voltage, for different magnetic fields. It is seen that these instabilities occur at the
same positions when the trapping voltage is expressed as a percentage of the maximum voltage, given by the stability limit.
The characteristic frequencies at which these instabilities occur, obey a relation that is given by n
zω
z + n
+ω
+ + n
-ω
- = 0, where ω
z, ω
+ and ω
- are the axial, perturbed cyclotron and the magnetron frequencies of the trapped electrons respectively, and the n's are integers. The reason for these instabilities are attributed to higher order static perturbations in the trapping potential.
Received 5 August 2002 / Received in final form 14 October 2002 Published online 17 December 2002
RID="a"
ID="a"Present address: Dept. of Physics, Rampurhat College, Rampurhat, Birbhum, West Bengal, India.
RID="b"
ID="b"e-mail: werth@mail.uni-mainz.de 相似文献
13.
A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells 总被引:1,自引:0,他引:1
N. Castagna G. Bison G. Di Domenico A. Hofer P. Knowles C. Macchione H. Saudan A. Weis 《Applied physics. B, Lasers and optics》2009,96(4):763-772
We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel
atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined
the intrinsic longitudinal, Γ
01, and transverse, Γ
02, relaxation rates. Our best cell shows Γ
01/2π≈0.5 Hz, and Γ
02/2π≈2 Hz. We find a strong correlation of both relaxation rates which we explain in terms of reservoir and spin exchange relaxation.
For each cell we have determined the optimal combination of rf and laser powers which yield the highest sensitivity to magnetic
field changes. Out of all produced cells, 90% are found to have magnetometric sensitivities in the range of 9 to 30 fT
. Noise analysis shows that the magnetometers operated with such cells have a sensitivity close to the fundamental photon
shot noise limit. 相似文献
14.
We consider one-dimensional (1D) interacting spinless fermions with a non-linear spectrum in a clean quantum wire (non-linear
bosonization). We compute diagrammatically the 1D dynamical structure factor, S(ω,q), beyond the Tomonaga approximation focusing
on it's tails, |ω| ≫vq,
i.e. the 2-pair excitation continuum due to forward scattering. Our methodology reveals three classes of diagrams: two “chiral”
classes which bring divergent contributions in the limits ω→±vq, i.e. near the single-pair excitation continuum, and a “mixed”
class (so-called Aslamasov-Larkin or Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be satisfied.
We relate our approach to the T=0 ones present in the literature. We also consider the
case and show that the 2-pair excitation continuum dominates the single-pair one in the range: |q|T/kF ≪ω±vq ≪T (substantial for q ≪kF). As applications we first derive the small-momentum optical conductivity due to forward scattering: σ∼1/ω for T ≪ω and σ∼T/ω2 for T ≫ω. Next, within the 2-pair excitation continuum, we show that the attenuation rate of a coherent mode of dispersion
Ωq crosses over from
, e.g. γq ∼|q|3 for an acoustic mode, to
, independent of Ωq, as temperature increases. Finally, we show that the 2-pair excitation continuum yields subleading curvature corrections
to the electron-electron scattering rate:
, where V is the dimensionless strength of the interaction. 相似文献
15.
16.
Coherent phonon and electron spectroscopy on surfaces using time-resolved second-harmonic generation
pump (ω)Eprobe
*(ω)|Eprobe(ω)|2. This is much easier to detect than transient grating, photon echo, or four-wave mixing schemes that use higher-order nonlinearities.
We have applied this technique to measure the energy gap and dephasing time of the dangling bond interband transition on the
GaAs(110)-relaxed (1×1) surface. Surface-carrier/surface-phonon interaction plays an important and perhaps dominant role in
surface carrier dephasing consistent with the larger electron-phonon coupling on the surface compared to the bulk.
Received: 13 October 1998 相似文献
17.
R. Mélin D. Feinberg 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):101-114
We derive a microscopic transport theory of multiterminal hybrid structures in which a superconductor is connected to several
spin-polarized electrodes. We discuss the non-perturbative physics of extended contacts, and show that such contacts can be
well represented by averaging out the phase of the electronic wave function. The intercontact Andreev reflection and elastic
cotunneling conductances are identical if the phase can be averaged out, namely in the presence of at least one extended contact.
The maximal conductance of a two-channel contact is proportional to (e
2/h)(a
0/D)2exp[-D/ξ(ω*)], where D is the distance between the contacts, a0 the lattice spacing, ξ(ω) is the superconducting coherence length, and ω* is the cross-over frequency between a perturbative regime ( ω < ω*) and a non perturbative regime ( ω* < ω < Δ).
Received 18 June 2001 and Received in final form 17 January 2002 相似文献
18.
R.B. López-Martens T.W. Schmidt G. Roberts 《Applied physics. B, Lasers and optics》2002,74(6):577-581
The cycle-averaged ac Stark effect associated with the [
A
]2Σ+v′=2?[
X
]2Π1/2v′=0 two-photon absorption of NO at intensities between 7.7 and 15.2 TW cm-2 has been characterized in real time through a synergic combination of bichromatic laser experiments and quantum-dynamics
calculations. Measurements of the fluorescence emitted by the Rydberg [
A
]2Σ+v′=2 level as a function of time between Stark and probe components of a bichromatic field exhibit a characteristic evolution
in temporal peak structure with Stark-field intensity, which is interpreted in terms of a time-dependent Floquet analysis
of the laser–matter interaction. The experimental observations are consistent with a dynamic Stark shift of Δεs(ω1,ω2)≤0.23 eV of the optical transition at these intensities.
Received: 18 January 2002 / Revised version: 6 March 2002 / Published online: 24 April 2002 相似文献
19.
K.-H. Yang C.-Z. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(3):409-415
In this paper we investigate the joint effects of the
electron-phonon interaction and an external alternating (ac) gate voltage
on the spectral density of shot noise through a vibrating quantum
dot system, by applying the Lang-Firsov canonical transformation and
the Keldysh nonequilibrium Green's function (NGF) technique. We find
that the effects of the electron-phonon and electron-photon interaction
on the differential shot noise are different. The main resonant peak of
the differential shot noise is decreased only when a time-dependent gate
voltage is imposed on quantum dot. With the ac field amplitude increasing,
the main resonant peak of the differential shot noise decreases. The Fano
factor of the system, which exhibits the deviation of shot noise from the
Schottky formula, is also studied. Super-Poissonian shot noise appears due
to the photon absorption (emission) processes in the low bias voltage region. 相似文献
20.
J. K. Baria 《Czechoslovak Journal of Physics》2004,54(4):469-485
A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic
interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C
11,C
12 andC
44), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C
12–C
44), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y
1), limiting value in the [110] direction (Y
2), degree of elastic anisotropy (A), maximum frequencyω
max, mean frequency 〈ω〉, 〈ω
2〉1/2=(〈ω〉/〈ω
−1〉)1/2, fundamental frequency 〈ω
2〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons
is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into
account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar
et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever
possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model
potential for predicting a large number of physical properties of transition metals. 相似文献