共查询到20条相似文献,搜索用时 31 毫秒
1.
A.E. Bernardini 《Annals of Physics》2009,324(6):1303-3263
The stationary phase method is frequently adopted for calculating tunneling phase times of analytically-continuous Gaussian or infinite-bandwidth step pulses which collide with a potential barrier. This report deals with the basic concepts on deducing transit times for quantum scattering: the stationary phase method and its relation with delay times for relativistic and non-relativistic tunneling particles. After reexamining the above-barrier diffusion problem, we notice that the applicability of this method is constrained by several subtleties in deriving the phase time that describes the localization of scattered wave packets. Using a recently developed procedure - multiple wave packet decomposition - for some specifical colliding configurations, we demonstrate that the analytical difficulties arising when the stationary phase method is applied for obtaining phase (traversal) times are all overcome. In this case, we also investigate the general relation between phase times and dwell times for quantum tunneling/scattering. Considering a symmetrical collision of two identical wave packets with an one-dimensional barrier, we demonstrate that these two distinct transit time definitions are explicitly connected. The traversal times are obtained for a symmetrized (two identical bosons) and an antisymmetrized (two identical fermions) quantum colliding configuration. Multiple wave packet decomposition shows us that the phase time (group delay) describes the exact position of the scattered particles and, in addition to the exact relation with the dwell time, leads to correct conceptual understanding of both transit time definitions. At last, we extend the non-relativistic formalism to the solutions for the tunneling zone of a one-dimensional electrostatic potential in the relativistic (Dirac to Klein-Gordon) wave equation where the incoming wave packet exhibits the possibility of being almost totally transmitted through the potential barrier. The conditions for the occurrence of accelerated and, eventually, superluminal tunneling transmission probabilities are all quantified and the problematic superluminal interpretation based on the non-relativistic tunneling dynamics is revisited. Lessons concerning the dynamics of relativistic tunneling and the mathematical structure of its solutions suggest revealing insights into mathematically analogous condensed-matter experiments using electrostatic barriers in single- and bi-layer graphene, for which the accelerated tunneling effect deserves a more careful investigation. 相似文献
2.
A.E. Bernardini 《The European Physical Journal C - Particles and Fields》2008,53(4):673-678
The general and explicit relation between phase times and dwell times for quantum tunneling or scattering is investigated.
Considering two identical propagating wave packets symmetrically impinging a one-dimensional barrier, here we demonstrate
that these two distinct transit time definitions give connected results where, for such a colliding configuration, the phase
time (group delay) accurately describes the exact position of the scattered particles. The analytical difficulties that arise
when the stationary phase method is employed for obtaining the phase (traversal) times are all overcome, since the multiple
wave packet decomposition allows us to recover the exact position of the reflected and transmitted waves. In addition to the
exact relation between the phase time and the dwell time, this leads to the right interpretation for both of them.
PACS 03.65.Xp 相似文献
3.
This paper presents results of a theoretical analysis of a new method for eliminating the Doppler broadening of spectral lines
and the broadening by the transit time of atoms through a light beam. The atomic motion in a one-dimensional standing wave
is studied and the conditions for translational-to-vibrational motion transformation are found. The variation in the Doppler
contour by the trapping effect is investigated. It is illustrated, in particular, that the width of the narrow peak at the
line centre depends mainly on the finite transit time of the atoms through the light beam. Next it is shown that, by accumulating
slow atoms in a three-dimensional standing wave, it is possible, in principle, to observe narrow peaks with their widths determined
only by the natural line width. The possibility of experimentally detecting of the phenomenon is discussed. 相似文献
4.
J. Weis O. Weis 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):135-146
This paper is concerned with the transmission time of an incident Gaussian wave packet through a symmetric rectangular barrier.
Following Hartman (J. Appl. Phys. 33, 3427 (1962)), the transmission time is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness
and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission
velocity which appears under certain conditions as a supervelocity, i.e. becomes larger than the corresponding propagation velocity in free space which is the group velocity for electrons or the
velocity of light for photons, respectively. By analysing the propagation of a broadband wave packet (which leads in free
space to an extremely concentrated wave packet at a certain time) we obtain the pulse response function of the barrier and
show that the insertion of the barrier is physically unable to produce a supervelocity. Therefore, the peak of an incident
Gaussian wave packet and the peak of the transmitted wave packet are in no causal relationship. The shape of the transmitted
wave packet is produced from the incident wave by convolution with the pulse response of the barrier. This yields a distortion
of the shape of the wave packet which includes also the observed negative time shift of the peak. We demonstrate further that
the phenomenon of Hartman's supervelocities is not restricted to barriers with their exponentially decaying fields but occurs
for instance also in transmission lines with an inserted LCR circuit.
Received 7 January 1999 and Received in final form 22 April 1999 相似文献
5.
A. E. Bernardini 《The European Physical Journal C - Particles and Fields》2008,56(4):545-556
We point out some incompatibilities which appear when one applies the stationary phase method for deriving phase times to
obtain the spatial localization of wave packets scattered by a unidimensional potential barrier. We concentrate on the above
barrier diffusion problem where the wave packet collision implies the possibility of multiple reflected and transmitted wave
packets, which, depending on the boundary conditions, can overlap or stand in relative separation in space. We demonstrate
that the indiscriminate use of the method for such a particular configuration leads to paradoxical results for which the correct
interpretation, confirmed by analytical/numerical calculations, imposes the necessity of the appearance of multiple peaks
as a consequence of multiple reflections by the barrier steps.
Also at Instituto de Física Gleb Wataghin, UNICAMP, PO Box 6165, 13083-970 Campinas, SP, Brazil. 相似文献
6.
The problem of electron resonant and non-resonant scatterings on two magnetized barriers is studied in the one-dimension. The transfer-matrix is built up to exactly calculate the coefficient of the electron transmittance through the system of two magnetic barriers with non-collinear magnetizations. The polarization of the transmitted electron wave for resonance and non-resonance transmittances is calculated. The transmittance coefficient and spin polarization can be drastically enhanced and controlled by the angle between the barrier magnetizations. 相似文献
7.
《Superlattices and Microstructures》1988,4(3):375-379
Novel heterostructure devices are comprised of potential barriers connected by short conductors. In this paper we present a simple theory for the transport properties of the barrier-conductor chain. The analysis is based on the solution of the Boltzmann equation supplemented by the boundary conditions provided by the barrier reflection and transmission probabilities. As an application of the theory the small signal equivalent circuit is constructed for the single and double barrier cases and for the infinite periodic chain. The high frequency properties of these structures are discussed. In general, the multibarrier structures show transit time resonances associated with multiple reflections. 相似文献
8.
9.
E. A. Vilkov 《Acoustical Physics》2005,51(5):524-532
The boundary-value problem of the magnetoelastic wave interaction with a moving domain wall in a ferromagnetic crystal is solved in the nonexchange magnetostatic approximation with allowance for the external magnetic field. It is shown that the difference introduced by magnetic field between the ferromagnetic resonance frequencies of the domains does not cause any noticeably departure of the refraction characteristics of reflected and transmitted waves from those observed at zero frequency mismatch. By contrast, the magnitudes of the transmission and reflection coefficients strongly depend on the external magnetic field and on the mobility of the domain wall. The dependence of the magnitude of the reflection coefficient on the external magnetic field at a fixed angle of shear wave incidence is found to possess two ferromagnetic resonance peaks. The positions and heights of the peaks may vary depending on the mobility of the domain wall. 相似文献
10.
Fifty years ago Hartman studied the barrier transmission time of wave packets (J Appl Phys 33:3427–3433, 1962). He was inspired by the tunneling experiments across thin insulating layers at that time. For opaque barriers he calculated faster than light propagation and a transmission time independent of barrier length, which is called the Hartman effect. A faster than light (FTL or superluminal) wave packet velocity was deduced in analog tunneling experiments with microwaves and with infrared light thirty years later. Recently, the conjectured zero time of electron tunneling was claimed to have been observed in ionizing helium inside the barrier. The calculated and measured short tunneling time arises at the barrier front. This tunneling time was found to be universal for elastic fields as well as for electromagnetic fields. Remarkable is that the delay time is the same for the reflected and the transmitted waves in the case of symmetric barriers. Several theoretical physicists predicted this strange nature of the tunneling process. However, even with this background many members of the physics community do not accept a FTL signal velocity interpretation of the experimental tunneling results. Instead a luminal front velocity was calculated to explain the FTL experimental results frequently. However, Brillouin stated in his book on wave propagation and group velocity that the front velocity is given by the group velocity of wave packets in the case of physical signals, which have only finite frequency bandwidths. Some studies assumed barriers to be cavities and the observed tunneling time does represent the cavity lifetime. We are going to discus these continuing misleading interpretations, which are found in journals and in textbooks till today. 相似文献
11.
Valery A. Loiko Vladimir V. Berdnik 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(14-16):1502-1510
A method describing light propagation in a plane-parallel light-scattering layer with large concentration of homogeneous particles is developed. It is based on the radiative transfer equation and the doubling method. The interference approximation is used to take into account collective scattering effects. Spectral dependence of transmitted light for a layer of nonabsorbing optically soft particles with subwavelength-sized particles is investigated. At small volume concentration of the particles the weak spectral dependences of wave exponents for coherently transmitted and diffuse light are observed. It is shown that in a layer with large volume concentration of the subwavelength-sized particles the wave exponent can exceed considerably the value of four, which takes place for the Rayleigh particles. The dependence of wave exponents for coherently transmitted and diffuse light on the refractive index and concentration of particles is investigated in detail. Multiple scattering of light results in the reduction of the exponent. The quantitative results are presented and discussed. It is shown that there is a range of wavelengths where the negative values of the wave exponent at the regime of multiple scattering are implemented. 相似文献
12.
D'Aguanno G Centini M Bloemer MJ Myneni K Scalora M Bowden CM Sibilia C Bertolotti M 《Optics letters》2002,27(3):176-178
Experiments show that the transit times of chirped, narrow-band pulses that move across nonabsorbing, one-dimensional barriers are modified dramatically by the interplay between the chirp and the transmission function of the sample. In an experiment we monitored 0.9-ns chirped, nearly Gaussian pulses as they traversed a 450-mum GaAs etalon. At certain wavelengths pulse transit times can be superluminal or even negative. To explain these phenomena we have proposed a generalization of the transit time for chirped pulses that is still meaningful even when the transit times are superluminal or negative. Our predictions agree well with the experimental results. 相似文献
13.
K. Korbel 《Isotopes in environmental and health studies》2013,49(2):67-69
The simpliest and most convenient in a practical use method of the flow rate measurement, based on the tracer technique, is a such one, in which the passing time of the “tracer wave” is determined. The results are then obtained as a diagram of radiation intensity in the chosen points of the pipeline. The passing of the tracer over these points is marked on a recording tape in a form of the characteristic peaks. Depending on the kind of flow, the recorded peaks take the different shapes. In the first order they depend on the velocity profile in the pipe cross section. This differentiation of velocities causes that, when the distance between the detecting probe and the injecting unit increases, the tracer wave becomes more diluted, involving consequently a corresponding lengthening and flattening of peaks. 相似文献
14.
Collinear light diffraction by three-frequency sound is investigated theoretically. The amplitude distributions of transmitted and diffracted light waves along the cell are calculated for different amplitudes of sound signals. The dependence of the intensity of principal diffraction peaks on the frequency difference between acoustic signal components is studied for different amplitude ratios of these components. It is shown that the character of this dependence for a wave being in synchronism differs substantially from that for two other waves characterized by detuning. The dependence of the amplitudes of principal and parasitic diffraction peaks on the efficiency of acoustooptical interaction is investigated. It is demonstrated that parasitic sideband components in diffracted light can play a considerable role if the diffraction efficiency is sufficiently high and exceeds 80%. 相似文献
15.
Investigations on AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes With Si‐Doped Quantum Barriers of Different Doping Concentrations
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Kangkai Tian Qian Chen Chunshuang Chu Mengqian Fang Luping Li Yonghui Zhang Wengang Bi Changqing Chen Zi‐Hui Zhang Jiangnan Dai 《固体物理学:研究快报》2018,12(1)
In this work, we investigate the impact of Si doped AlGaN quantum barriers on the optical powers for [0001] oriented III‐nitride based deep‐ultraviolet light‐emitting diodes (DUV LEDs). The polarization‐induced electric field in the active region is screened as the result of Si‐doped quantum barriers, which gives rise to the improved spatial overlap between electron and hole wave functions. The polarization screening effect within the quantum wells is further proven by the observation of the blue shift for the wavelength. However, the hole distribution across the active region can be significantly retarded if the Si dosage in the quantum barriers is too high. Therefore, the improved radiative recombination within the active region can be realized provided that the Si dosage in the quantum barriers is moderately adjusted to guarantee both the better hole injection efficiency and the screened polarization effect in the multiple quantum wells. 相似文献
16.
为了研究直达表面波在圆弧过渡面处传播性能的变化,采用有限元方法模拟了热弹机制下,线性脉冲激光辐照金属铝块表面时激发的表面波在近表面传播过程中,在不同曲率半径的圆弧处发生的反射及透射现象,建立了圆弧半径与反射表面波以及透射表面波时域信号特征之间的联系。计算结果表明:曲率半径与表面波中心波长的数值关系对表面波在圆弧处的传播有显著的影响;同时证明了根据透射表面波信号的到达时间可以反演圆弧半径的大小,为之后利用表面波信号定量检测材料表面圆弧凹痕的深度提供了理论依据。 相似文献
17.
In analogy with the definition of resonant or quasi-bound states used in three-dimensional quantal scattering, we define the
quasi-bound states that occur in one-dimensional transmission generated by twin symmetric potential barriers and evaluate
their energies and widths using two typical examples: (i) twin rectangular barrier and (ii) twin Gaussian-type barrier. The
energies at which reflectionless transmission occurs correspond to these states and the widths of the transmission peaks are
also the same as those of quasi-bound states. We compare the behaviour of the magnitude of wave functions of quasi-bound states
with those for bound states and with the above-barrier state wave function. We deduce a Breit-Wigner-type resonance formula
which neatly describes the variation of transmission coefficient as a function of energy at below-barrier energies. Similar
formula with additional empirical term explains approximately the peaks of transmission coefficients at above-barrier energies
as well. Further, we study the variation of tunnelling time as a function of energy and compare the same with transmission,
reflection time and Breit-Wigner delay time around a quasi-bound state energy. We also find that tunnelling time is of the
same order of magnitude as lifetime of the quasi-bound state, but somewhat larger. 相似文献
18.
A.E. Bernardini 《The European Physical Journal C - Particles and Fields》2007,49(3):891-896
After reexamining the above-barrier diffusion problem where we notice that the wave packet collision implies the existence
of multiple reflected and transmitted wave packets, we analyze the way of obtaining phase times for tunneling/reflecting particles in
a particular colliding configuration where the idea of multiple peak decomposition is recovered. To partially overcome the
analytical incongruities which frequently arise when the stationary phase method is adopted for computing the (tunneling)
phase-time expressions, we present a theoretical exercise involving a symmetrical collision between two identical wave packets
and a unidimensional squared potential barrier where the scattered wave packets can be recomposed by summing the amplitudes
of simultaneously reflected and transmitted wave components so that the conditions for applying the stationary phase principle
are totally recovered. Lessons concerning the use of the stationary phase method are drawn.
PACS 02.30.Mv, 03.65.Xp 相似文献
19.