共查询到20条相似文献,搜索用时 31 毫秒
1.
M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):151-153
Using the Landauer formula approach, it is proven that
minimal conductivity of order e2/h found experimentally in
bilayer graphene is an intrinsic property. For the case of ideal
crystals, the conductivity turns out to be equal to e2/2h per
valley per spin. A zero-temperature shot noise in bilayer graphene
is considered and the Fano factor is calculated. Its value
1–2/π is close to the value 1/3 found earlier for single-layer
graphene. 相似文献
2.
3.
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
4.
Ulrike Herzog 《Annalen der Physik》1991,503(8):594-600
The intensity noise spectrum is investigated quantum-mechanically for incident coherent light passing through a resonator which is filled with a k-photon-absorber. For k? 2 the noise of the outgoing light is reduced below the shot noise level the reduction being maximal for frequencies that are small in comparison to the cavity bandwidth. It turns out that the highest possible value of this low-frequency noise reduction is obtained when the resonator losses due to transmission through the outcoupling mirror are 2k – 1 times as large as the k-photon absorption losses. In this case the noise at zero frequency is reduced with respect to the shot noise level by a factor of k/(2k – 1). 相似文献
5.
O. Filippov K.H. Ringhofer B.I. Sturman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):285-290
Analytically and numerically we investigate the dependence of the first Fourier harmonics of the space-charge field, induced
in an AC-biased sillenite crystal by a light-interference pattern, on the light contrast m. It is shown that within the whole contrast range, 0 < m < 1, these dependences are controlled by the only scalar parameter - the space-charge wave quality factor Q. In the low-contrast limit, m Q
-2, this factor defines the degree of enhancement of the nonlinear response while for larger contrasts it characterizes strong
saturation effects. The data obtained are compared with the results of the previous studies of the AC-response. The possibilities
of experimental detection of predicted dependences and their possible implications are discussed.
Received 13 September 2002 / Received in final form 27 December 2002 Published online 11 February 2003 相似文献
6.
K. Maniadaki L.A.A. Nikolopoulos P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):205-209
We present detailed calculations for one- and two-photon above-threshold detachment (ATD) cross-sections of the negative positronium
ion Ps
-
(
e
+
e
-
e
-
), below the threshold of Ps(n
= 2), using a configuration interaction (CI) method on a B splines basis. Both the one- and two-photon detachment cross-sections
have a form similar to the corresponding spectra of the H- ion, scaled accordingly. The peak value of the one-photon cross-section agrees very well with the calculations by Bathia
and Drachman [1], while it differs from those by Igarashi et al. [2], which give a value of 15% lower. Two-photon detachment cross-sections are also reported.
Received 24 January 2002 / Received in final form 9 April 2002 Published online 19 July 2002 相似文献
7.
Within the Nuclear Nambu-Jona-Lasinio model of light nuclei (the NNJL model), describing strong low-energy nuclear interactions, we compute the width of the energy level of the ground state of pionic deuterium. The theoretical value fits well the experimental data. Using the cross-sections for the reactions e + d p + p + e- and e + d p + n + e, computed in the NNJL model, and the experimental values of the events of these reactions, detected by the SNO Collaboration, we compute the boron neutrino fluxes. The theoretical values agree well with the experimental data and the theoretical predictions within the Standard Solar Model by Bahcall. We argue the applicability of the constraints on the astrophysical factor for the solar proton burning, imposed by helioseismology, to the width of the energy level of the ground state of pionic deuterium. We show that the experimental data on the width satisfy these constraints. This testifies an indirect measurement of the recommended value of the astrophysical factor for the solar proton burning in terrestrial laboratories in terms of the width of the energy level of the ground state of pionic deuterium. 相似文献
8.
A.V. Papoyan M. Auzinsh K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):63-71
We report results of a theoretical and experimental study of the ground state nonlinear Hanle effect under strong laser excitation.
It is shown that besides the well-known zero-magnetic field suppression of absorption on F
g = F→F
e = F - 1 transitions caused by population trapping, an optical pumping induced enhanced absorption occurs on F
g = F→F
e = F + 1 transitions for small B-fields. The latter effect becomes more pronounced for high F values. The experiment with atomic vapor of Cs (D2 line, F
g = 4) confirms an increase of the spectrally unresolved fluorescence yield at zero magnetic field and 600 mW/cm2 laser intensity by 9% or 42%, when excitation occurs with linearly or circularly polarized light, respectively. The results
of the experiment agree with numerical simulation studies using equations of motion for a density matrix.
Received 24 November 2001 / Received in final form 25 March 2002 Published online 24 September 2002 相似文献
9.
We present experimental evidence that the free-electron laser at the TESLA Test Facility has reached the maximum power gain
of 107 in the vacuum ultraviolet (VUV) region at wavelengths between 80 and 120 nm. At saturation the FEL emits short pulses with
GW peak power and a high degree of transverse coherence. The radiation pulse length can be adjusted between 30 fs and 100
fs. Radiation spectra and fluctuation properties agree with the theory of high gain, single-pass free-electron lasers starting
from shot noise.
Received 26 April 2002 Published online 28 June 2002 相似文献
10.
M.A. Lebeault J. Viallon J. Chevaleyre C. Ellert D. Normand M. Schmidt O. Sublemontier C. Guet B. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):233-242
We exposed small size-controlled lead clusters with a few hundreds of atoms to laser pulses with peak intensities up to 1015 W cm-2 and durations between 60 fs to 2.5 ps. We measured kinetic energies and ionic charge of fragments as a function of the laser
intensity and pulse duration. Highly charged Pbn+ ions up to n = 26 have been detected presenting kinetic energies up to 15 keV. For comparison with our experimental results, we have performed
simulations of the laser coupling with a cluster-sized lead nanoplasma using a qualitative model that was initially proposed
by Ditmire and co-workers at LLNL for the case of rare gas clusters. From these simulations we conclude that two mechanisms
are responsible for the explosion dynamics of small lead clusters. As already observed for large rare gas clusters (n = 106), fragments with charge states below +10 are driven by Coulomb forces, whereas the higher charged fragments are accelerated
by hydrodynamic forces. The latter mechanism is a direct consequence of the strong laser heating of the electron cloud in
the nanoplasma arising from a plasmon-like resonance occurring at n
e = 3n
c. In order to obtain an optimized laser-nanoplasma coupling, our results suggest that the plasma resonance should occur at
the peak intensity of the laser pulse. Due to inertial effects, even for such small-sized clusters, the observed optimum pulse
duration is in the order of 1 ps which is in good agreement with our theoretical results.
Received 18 March 2002 Published online 19 July 2002 相似文献
11.
X.-M. Hu J.-S. Peng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):291-299
On the basis of the nondegenerate quantum-beat laser model, we introduce a coherent field which drives the transition between the upper lasing level and an
auxiliary level. We demonstrate that such a four-level system can produce squeezed two-mode laser without and with inversion.
When the laser is operated well above threshold, the intensity fluctuation in the average mode is reduced below the shot noise
with an optimum Mandel parameter Q=- 1/2. At the same time, the noises in the relative amplitude and the relative phase drop to their vaccum noise levels. Furthermore,
regardless of inversion, noninversion, and transition between inversion and noninversion, the optimum Mandel Q parameter of Q=- 1/2 is retained when the system operates well above threshold. A simple physical explanation of the squeezing mechanism
for two-mode squeezing is given.
Received: 22 December 1997 / Revised: 25 March 1998 / Accepted: 9 September 1998 相似文献
12.
Stochastic multiresonance in a bistable sawtooth potential driven by correlated multiplicative and additive noise 总被引:1,自引:0,他引:1
J. Wang L. Cao D.J. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):123-128
We present an analytic investigation of the signal-to-noise ratio (SNR) by studying the bistable sawtooth system driven by correlated Gaussian white noises. The analytic expression of SNR is obtained. Based on it, we detect the phenomenon of stochastic multiresonance, which arises from the dependence of SNR upon the noises correlation coefficient. Furthermore, there exists not only resonance, but also suppression in the SNR∼D (the additive noise intensity) curve and the SNR∼Q (the multiplicative noise intensity) curve.
Received 26 February 2002 / Received in final form 12 July 2002 Published online 17 September 2002 相似文献
13.
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
14.
Jian-Hui Yuan Ze ChengJian-Jun Zhang Qi-Jun ZengJun-Pei Zhang 《Physics letters. A》2011,375(27):2670-2675
We study theoretically shot noise and minimal conductivity of electrons by evanescent states penetrating through clean graphene nanoribbons (GNRs). With increasing of the barrier voltage, we find that the minimum conductivity will increase to 4e2/πh and the maximum Fano factor will increase to 1/3. More interestingly, quantum oscillations can be tuned by the gate voltage and separated by tuning the barrier voltage 相似文献
15.
We use large-scale Monte Carlo simulations to test scaling theories for the electrostatic persistence length l
e of isolated, uniformly charged polymers with Debye-Hückel intrachain interactions in the limit where the screening length
κ-1 exceeds the intrinsic persistence length of the chains. Our simulations cover a significantly larger part of the parameter
space than previous studies. We observe no significant deviations from the prediction l
e∝κ-2 by Khokhlov and Khachaturian which is based on applying the Odijk-Skolnick-Fixman theories of electrostatic bending rigidity
and electrostatically excluded volume to the stretched de Gennes-Pincus-Velasco-Brochard polyelectrolyte blob chain. A linear
or sublinear dependence of the persistence length on the screening length can be ruled out. We show that previous results
pointing into this direction are due to a combination of excluded-volume and finite chain length effects. The paper emphasizes
the role of scaling arguments in the development of useful representations for experimental and simulation data.
Received 12 February 2002 相似文献
16.
Dalitz decays of ω and ρ mesons,
and
, produced in pp collisions are calculated within a covariant effective meson-nucleon theory. We argue that the ω transition form factor
is experimentally accessible in a fairly model-independent way in the reaction pp → ppπ0
e
+
e
- for invariant masses of the π0
e
+
e
- subsystem near the ω pole. Numerical results are presented for the intermediate-energy kinematics of envisaged HADES experiments. 相似文献
17.
C. -D. Lien M. -A. Nicolet C. S. Pai S. S. Lau 《Applied Physics A: Materials Science & Processing》1985,36(3):153-157
We have investigated the reaction of a thin Co film with a (100) Si (Si
c
) or an evaporated Si (Si
e
, which is amorphous) substrate during thermal annealing. On either substrate, Co2Si and CoSi form simultaneously and the growth of each phase has a square root of time dependence. Both silicides grow faster on Si
c
than on Si
e
. A model is proposed to calculate the effective diffusion constant in each silicide from the growth data of the silicides. The activation energies of the effective diffusion constants in Co2Si and CoSi grown on Si
c
are 1.7±0.1 eV and 1.8±0.1 eV, respectively; while those on Si
e
are 1.85±0.1 eV and 1.9 ±0.1 eV, respectively. The differences observed for the two substrates are tentatively attributed to the presence of impurities in Sie and to the microstructural differences of the silicides formed on either substrate. 相似文献
18.
M. Lontano D. Ryutov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):347-351
We demonstrate the in situ detection of cold 87Rb atoms near a dielectric surface using the absorption of a weak, resonant evanescent wave. We have used this technique in
time of flight experiments determining the density of atoms falling on the surface. A quantitative understanding of the measured
curve was obtained using a detailed calculation of the evanescent intensity distribution. We have also used it to detect atoms
trapped near the surface in a standing-wave optical dipole potential. This trap was loaded by inelastic bouncing on a strong,
repulsive evanescent potential. We estimate that we trap 1.5×104 atoms at a density 100 times higher than the falling atoms.
Received 14 May 2002 Published online 8 October 2002
RID="a"
ID="a"e-mail: spreeuw@science.uva.nl 相似文献
19.
The cross-sections for the reactions of muonium (anti-muonium) production in the high-energy electron (positron) scattering
by nuclei e
-(e
+) + Z↦Z + M
0(ˉM) + μ-(μ+) are calculated in dependence on energy and polarization of the initial electron (positron) and polarization of the final
μ-(μ+)-meson. Since this is a coherent phenomenon the cross-sections are proportional to Z2. For Z ∼ 100, due to the factor Z2, the cross-sections are large enough to be measured at the energies available for the HERA Collider at DESY. The results
are discussed in connection with a test of CPT invariance.
Received: 24 September 2002 / Accepted: 12 March 2003 / Published online: 27 May 2003 相似文献
20.
Aseshkrishna Datta A. Djouadi M. Mühlleitner 《The European Physical Journal C - Particles and Fields》2002,25(4):539-551
We analyze the associated production at future high-energy e
+
e
-
colliders, of first generation sleptons with neutralinos and charginos in the modes e
+
e
-
and , in the framework of the minimal supersymmetric extension of the standard model. We show that the production rates, in particular
for associated production of right-handed selectrons and the lightest neutralino which in general is the first accessible
kinematically, can be much larger than the corresponding ones for second and third generation scalar leptons and for scalar
quarks. With the high luminosities expected at these colliders, the detection of first generation sleptons with masses significantly
above the kinematical two-body threshold, , is thus possible in favorable regions of the parameter space.
Received: 27 June 2002 / Published online: 20 September 2002 相似文献