共查询到20条相似文献,搜索用时 15 毫秒
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Lotfi ZekriAhmed Kaiss Jean-Pierre ClercBernard Porterie Nouredine Zekri 《Physics letters. A》2011,375(3):346-351
Percolation properties and d.c. conductivity were determined for an L2×h-random resistor network model of metal-insulator composite films. The effects of the thickness h on the percolation threshold and conductivity were studied numerically in the limit of an infinite size of the L2-plane parallel to the film. For thicknesses ranging from h/L=0.01 to h/L=0.24, a crossover between a finite-size regime and a saturation regime was observed at h/L≈0.1. In the finite-size regime (h/L?0.01), the percolation threshold scales as pc(h)−pc3∝h−1/x, the exponent x being compatible with that of the critical exponent of the 3D correlation length, ν3. The conductivity exponent t appeared to depend linearly on the ratio h/L with a slope νD compatible with 2+ν2, where ν2 is the 2D correlation length exponent. In the saturation regime, a scaling correction for the percolation threshold was found with an exponent 1+1/ν3. In this regime we also observed a logarithmic dependence of the conductivity exponent on h/L. 相似文献
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V. A. Sablikov 《JETP Letters》2006,84(7):404-408
It is shown that the electron transport through junctions between one-and a two-dimensional systems and through quantum point contacts is considerably affected by the interaction of electrons belonging to different subbands. The interaction mechanism is related to Friedel oscillations, which are produced by the electrons of the closed subbands even in smooth transitions. Because of the interaction with these oscillations, electrons of the open subbands experience a backscattering. The electron reflection coefficient has a sharp peak at the energy equal to the Fermi energy and may reach a value of about 0.1. This result allows one to explain a number of available experimental facts. 相似文献
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Longhi S 《Optics letters》2007,32(5):557-559
Engineered optical waveguide structures with a controlled photon tunneling rate are shown to provide an experimentally accessible optical system to test universal features of dynamic control of quantum mechanical decay [Phys. Rev. Lett. 87, 270405 (2001)]. Examples of deceleration and acceleration of photon tunneling, as well as of suppression of fractional decay, are presented for a periodically curved waveguide coupled to a semi-infinite waveguide array. 相似文献
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We show that smooth variations, delta n(r), of the local electron concentration in a clean 2D electron gas give rise to a zero-bias anomaly in the tunnel density of states, nu(omega), even in the absence of scatterers, and thus, without the Friedel oscillations. The energy width, omega 0, of the anomaly scales with the magnitude, delta n, and characteristic spatial extent, D, of the fluctuations as (delta n/D)2/3, while the relative magnitude delta nu/nu scales as (delta n/D). With increasing omega, the averaged delta nu oscillates with omega. We demonstrate that the origin of the anomaly is a weak curving of the classical electron trajectories due to the smooth inhomogeneity of the gas. This curving suppresses the corrections to the electron self-energy which come from the virtual processes involving two electron-hole pairs. 相似文献
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Tunneling to both one and two or three subbands of the 2D electron system of a delta-doped layer is observed in Al/δ-GaAs structures. The energy positions of 2D subbands in one sample are varied due to the diamagnetic shift or persistent tunneling photoconductivity. The change of the sign of a step in tunneling conductivity is observed at the threshold of the emission of an LO phonon when a successive subband is involved in tunneling. An increase in conductivity (positive step) is observed for inelastic intrasubband electron-phonon scattering. A decrease in conductivity (negative step) is observed when the ordinary processes of inelastic tunneling are supplemented by intersubband transitions of electrons that have tunneled in 2D electron systems with the emission of an LO phonon. 相似文献
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Paul K. Hansma 《Physics Reports》1977,30(2):145-206
Inelastic Electron Tunneling Spectroscopy (IETS) is a new technique for measuring the vibrational spectrum of minute quantities of organic compounds. Sensitivity is its key advantage over the conventional techniques of infrared and Raman spectroscopy. This article will first discuss the technique itself: its theoretical basis, selection rules, sensitivity, vibrational mode shifts due to surface interactions and superconductivity, and sample preparation. Then it will discuss applications of the technique to problems in biology, radiation physics, surface physics, and catalysis. 相似文献
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We measure photon-assisted tunneling in 4- and 6-junction electron pumps at photon frequencies up to 60 GHz. We determine the microwave voltage at the pumps using noise thermometry. The standard theory of leakage in the electron pump, modified to include photon-assisted tunneling, describes our experiments well. From this test of theory we argue that, in the absence of external microwaves, photon-assisted tunneling driven by 1/f noise is an important error mechanism in electron pumps. 相似文献
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We have calculated the quantum conductance of single-walled
carbon nanotube (SWNT) waveguide by using a tight binding-based
Greens function approach. Our calculations show that the slow
conductance oscillations as well as the fast conductance
oscillations are manifestations of the intrinsic quantum
interference properties of the conducting SWNTs, being independent
of the defect and disorder of the SWNTs. And zigzag type tubes do
not show the slow oscillations. The SWNT electron waveguide is
also found to have distinctly different transport behavior
depending on whether or not the length of the tube is commensurate
with a (3N+1) rule, with N the number of basic carbon repeat
units along the nanotube length. 相似文献
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Resonant tunneling is accompanied by the accumulation of 2D electrons in the quantum well between the barriers of resonant
tunneling diodes. In high-quality structures this gives a Z-shaped current-voltage characteristic, and it is shown that self-excitation of 2D plasmons occurs in this quantum well for
any external circuit at completely realistic parameters of the structures.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 628–633 (25 October 1998) 相似文献
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J. G. Cui W. D. Li 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):187-191
The propagation of an initially-localized optical beam along two
coupled modulated waveguides is investigated. A universal step-like
structure emerges in the propagation process once |d|\delta
v/v0|v_0| ~ 1 and T = 2 π/m v0m v_0, both for the linear and nonlinear
optical waveguides. The reason is that the coupling between the two
waveguides can be completely suppressed at z = m
T or (2 m+1)T/2.
When the nonlinearity is strong, assisted tunneling can be found for
the initially-localized optical beam by slightly increasing the
strength of the modulation. 相似文献
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V. M. Svistunov Yu. V. Medvedev V. Yu. Tarenkov A. I. D’yachenko E. Hatta M. Mukasa R. Aoki H. Szymczak S. Lewandowski J. Leszczynski 《Journal of Experimental and Theoretical Physics》2000,91(3):547-552
Tunneling experiments were performed on ceramic samples with the composition La0.6Sr0.4MnO3, manifesting negative magnetoresistance. Two types of contacts were studied: symmetric (break junction type) and asymmetric ceramic-insulator-metal contact. A high magnetic-field sensitivity of the conductivity σ(H) of the contacts was observed even when only one of the electrodes was magnetic. The effect was explained by the existence of spin-polarized localized states in the tunneling barrier. Their appearance was attributed to the formation of an oxygen-depleted, magnetically two-phase state of localized ferromagnetic nanoregions in an anti-ferromagnetic dielectric matrix in the near-contact region. 相似文献
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LIU DuanYang XIA JianBai & CHANG YiaChung State Key Laboratory for Superlattices Microstructures 《中国科学:物理学 力学 天文学(英文版)》2010,(1)
The properties of Rashba wave function in the planar one-dimensional waveguide are studied, and the following results are obtained. Due to the Rashba effect, the plane waves of electron with the energy E divide into two kinds of waves with the wave vectors k 1 =k 0 +k δ and k 2 =k 0 -k δ , where k δ is proportional to the Rashba coefficient, and their spin orientations are +π/2 (spin up) and -π/2 (spin down) with respect to the circuit, respectively. If there is gate or ferromagnetic contact in the circuit, the Rashba wave function becomes standing wave form exp(±ik δ l)sin[k 0 (l-L)], where L is the position coordinate of the gate or contact. Unlike the electron without considering the spin, the phase of the Rashba plane or standing wave function depends on the direction angle θ of the circuit. The travel velocity of the Rashba waves with the wave vector k 1 or k 2 are the same hk0/m * . The boundary conditions of the Rashba wave functions at the intersection of circuits are given from the continuity of wave functions and the conservation of current density. Using the boundary conditions of Rashba wave functions we study the transmission and reflection probabilities of Rashba electron moving in several structures, and find the interference effects of the two Rashba waves with different wave vectors caused by ferromagnetic contact or the gate. Lastly we derive the general theory of multiple branches structure. The theory can be used to design various spin polarized devices. 相似文献
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《Superlattices and Microstructures》1998,24(5):321-335
The transport properties of corner reflectors have been studied using a method derived from the embedding method for confined quantum systems. The method is used to calculate the eigenstates and Green function which are expanded in any convenient basis set and then used to calculate the transmission and reflection coefficients. The results for the reflectors are compared to the results for a right-angled corner and a circular corner. Current flow studies have been done to clarify the transmission results. The local density of states for the corners are calculated to study bound states and resonances. The reflectors have both one-dimensional and two-dimensional densities of states depending on the size of the reflector. 相似文献
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《Superlattices and Microstructures》1995,18(2):121-130
We use a modulation-doped double barrier heterostructure to fabricate a resonant tunneling single electron transistor. Irregular Coulomb blockade oscillations are observed when the gate voltage is swept to vary one-by-one the number of electrons in the dot close to 'pinch-off'. The oscillation period is not regular, and generally becomes longer as the electron number is decreased down to zero, reflecting the growing importance of electron-electron interactions and size quantization. Negative differential resistance associated with resonant tunneling through zero-dimensional states is pronounced for a dot holding just a few electrons. The temperature dependence of the Coulomb blockade oscillations and that for the negative differential resistance are not the same. This highlights the different effects of charging and resonant tunneling on the transport characteristics. 相似文献