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1.
Magnetotransport in a dual waveguide coupled by a finite barrier: Energy filter and directional coupler
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We propose in this paper that a dual waveguide coupled by a finite
barrier be able to serve as an energy filter under a perpendicular
magnetic field. In the waveguide direction, the conductance exhibits
a periodic square-wave pattern in which the miniband is controlled
by the magnetic and potential modulation. The electrons with
energies in the miniband can completely transfer along one waveguide
while the other electrons undergo filtration. Compared with the
coupled waveguide without magnetic modulation, the structure under
magnetic field is found to be a good directional coupler. By
adjusting the potential barrier and magnetic field, the electrons
input from one port of waveguide can transfer to any other ports. 相似文献
2.
3.
The quantum conductance for electrons scattering from a uniform scatterer in a narrow-wire semiconductor is calculated. Instead of getting the conductance directly from the calculation of transmission coefficient, we calculate the reflection coefficient instead. The transmission coefficient is then calculated by using the conservation law, T=I−R. This alternative method can avoid the instability of the conductance obtained by including more evanescent modes for a finite-range scatterer in a narrow-wire semiconductor. This method is applied to a semi-infinite strip potential barrier and a rectangular potential barrier in a narrow wire. The quantum stepwise conductance is obtained in both cases. For a repulsive rectangular potential barrier, there are oscillations in each stepwise conductance. For an attractive rectangular potential barrier, there exist multiple quasi-bound states below the sub-band energies which can cause the drop of the quantum conductance. The effect of the continuum quasi-bound states diminishes as the energy of the incident electron increases, but the influence of the discrete quasi-bound states still persists. 相似文献
4.
A. M. Babanl? S. Bah?eli D. Türk?z Altu? 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(1):133-138
The energy spectrum, ballistic conductance of an electron on the surface of a Kane type semiconductor hollow cylinder has been calculated by using the Kane equation with an additional term that takes into account the spin-orbit (SO) interaction. This term, known as Rashba term, occurs for asymmetric quantum wells, where two directions on the normal n are physically nonequivalent. If Rashba spin-orbital interaction is incorporated into energy spectrum, it leads to the emergence of new extrema. We obtained electron energy spectrum, which depends on the sign of the effective spin orbital constant. The energy spectrum of electrons has two branches when the magnetic field does not exist. One of these branches has only one minimum while the other branch has one maximum around k = 0 and two minima. The external magnetic field can control these extrema which occur in the event transport. The results were used to obtain the ballistic conductance at finite temperature of the Kane type hollow cylinder. It has been found that the presence of additional local extremum points in the subband of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential. The g-factor of electrons was observed to depend on Rashba parameter in a linear manner. The effect of finite temperature smears out the sharp steps in the zero-temperature conductance. 相似文献
5.
M. Hannan R. W. Giannetta T. Grundbacher I. AdesidaJ. Eom V. Chandrasekhar 《Superlattices and Microstructures》1996,20(4):427-433
Transport phenomena in a double-bend quantum structure fabricated in the two-dimensional electron gas of a modulation doped GaAs/AlGaAs structure, are studied experimentally. The structure consists of an electrostatically defined quantum dot with two one-dimensional wires connected on opposite corners of the dot. The current–voltage characteristics of such devices exhibit quantized conductance breakdown (non-linear behavior), conductance variation with confinement, and non-linear and asymmetric behavior at high bias condition. Low temperature conductance of this structure shows evidence of resonant tunneling, while the peaks of the conductance vary with temperature. 相似文献
6.
We present model calculations for the Landauer conductance of tunnel junctions. The tunnelling of free electrons through a rectangular potential barrier is considered. The conductance of a finite number of barriers was calculated using a transfer matrix method. The periodic arrangement of the same barriers was described by a Kronig–Penney model to calculate the band structure and, from that, the conductance of a point contact in the ballistic limit. Comparison of the results showed the importance of the boundary conditions. Caused by resonant scattering in the superlattice, the conductance is overestimated by an order of 1/t, the transmission coefficient of the single barrier. In the case of metallic multilayers, these interferences are of minor importance. In conclusion, the application of the Landauer formula to periodic lattices to describe the tunnelling conductance of a single barrier is not appropriate. 相似文献
7.
An exact self-consistent solution for a finite temperature quantum-ordered state of correlated electron system found previously (8 and 1) is used to derive the fermionic single-particle Green's function. The quantum order parameter (QOP) found in the form of a periodic (elliptic Jacoby) function of the Matsubara's imaginary time (Mukhin, 2009), plays the role of effective scattering potential seen by electrons. The analytic solution for the Green's function demonstrates the following new features: (1) the pseudo-gap behavior of the single-electron density of states (DOS) near the (shifted) Fermi-level;(2) the side-bands of decreasing intensity away from the Fermi-level; (3) scaling of the quasi-particle energies with the QOP amplitude; (4) fermionic quasi-particles in the QOP state are combined from two confined “odd” and “even” fermions that separately would be unstable. The false-color plot of single-fermion DOS in the limit of a periodic kink-like Matsubara time-dependence of QOP is presented and could be used as prediction for the ARPES experiments. The plot of the DOS transfer between different energies at the “fermi-surface” momentum for a given kink-like QOP is also presented. Some possibly observable consequences of the found finger-prints are discussed. 相似文献
8.
We study electrons tunneling through a double-magnetic-barrier structure on the surface of monolayer graphene.The transmission probability and the conductance are calculated by using the transfer matrix method.The results show that the normal incident transmission probability is blocked by the magnetic vector potential and the Klein tunneling region depends strongly on the direction of the incidence electron.The transmission probability and the conductance can be modulated by changing structural parameters of the barrier,such as width and height,offering a possibility to control electron beams on graphene. 相似文献
9.
We investigate the influence of electromagnetic fluctuations on quantum transport in a two-dimensional electron gas. We calculate the conductance of a quantum point contact under the influence of transport and gate-voltage fluctuations at finite temperature, using a generalized Landauer-Büttiker approach. The fluctuations are described by a suitable bath of bosons. In contrast to fluctuations of the gate-voltage, transport voltage fluctuations can completely block the electron transport at T = 0. This blockade is lifted as a result of finite temperature of the electrons in the Fermi reservoirs and also of the coupled bosons. In a typical experiment, these two temperatures need not to be the same. We show that the temperature of the coupled bosons limits the accuracy of the conductance quantization of a quantum point contact to a few percent. 相似文献
10.
We show that quantum dots and quantum wires are formed underneath metal electrodes deposited on a planar semiconductor heterostructure containing a quantum well. The confinement is due to the self-focusing mechanism of an electron wave packet interacting with the charge induced on the metal surface. Induced quantum wires guide the transfer of electrons along metal paths and induced quantum dots store the electrons in specific locations of the nanostructure. Induced dots and wires can be useful for devices operating on the electron spin. An application for a spin readout device is proposed. 相似文献
11.
We study a junction of three quantum wires enclosing a magnetic flux. This is the simplest problem of a quantum junction between Tomonaga-Luttinger liquids in which Fermi statistics enter in a nontrivial way. We present a direct connection between this problem and the dissipative Hofstadter problem, or quantum Brownian motion in two dimensions in a periodic potential and an external magnetic field, which in turn is connected to open string theory in a background electromagnetic field. We find nontrivial fixed points corresponding to a chiral conductance tensor leading to an asymmetric flow of the current. 相似文献
12.
《Superlattices and Microstructures》1998,23(6):1227-1230
We theoretically investigate the ballistic conductance of hollow quantum wires made of a two-dimensional electron gas occupying a cylindrical surface. The dependence of the conductance on the electron Fermi momentum differs drastically from the conventional case of a strip-like wire. We trace the evolution between these two cases in an exactly solvable model of a circular cylinder affected by a δ-like potential barrier along its element. We consider also a cylinder with two diametrically opposite δ-function barriers, the case representing somewhat realistic semiconductor structures. The general consequences of the boundary condition topology are also discussed. 相似文献
13.
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
14.
15.
R. T.?Senger B.?Kozal A.?Chatterjee A.?Er?elebi 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(4):525-529
The bipolaronic ground state of two electrons in a spherical
quantum dot or a quantum wire with parabolic boundaries is studied in the strong electron-phonon coupling regime. We introduce
a variational wave function that can conveniently
conform to represent alternative ground state configurations of the two electrons,
namely, the bipolaronic bound state, the state of two individual
polarons, and two nearby interacting polarons confined by the
external potential. In the bipolaron state the electrons are found to be
separated by a finite distance about a polaron size. We present the formation
and stability criteria of bipolaronic phase in confined media. It
is shown that the quantum dot confinement extends the domain of
stability of the bipolaronic bound state of two electrons as
compared to the bulk geometry, whereas the quantum wire geometry
aggravates the formation of stable bipolarons. 相似文献
16.
We study finite quantum wires and rings in the presence of a charge-density wave gap induced by a periodic modulation of the chemical potential. We show that the Tamm-Shockley bound states emerging at the ends of the wire are stable against weak disorder and interactions, for discrete open chains and for continuum systems. The low-energy physics can be mapped onto the Jackiw-Rebbi equations describing massive Dirac fermions and bound end states. We treat interactions via the continuum model and show that they increase the charge gap and further localize the end states. The electrons placed in the two localized states on the opposite ends of the wire can interact via exchange interactions and this setup can be used as a double quantum dot hosting spin qubits. The existence of these states could be experimentally detected through the presence of an unusual 4π Aharonov-Bohm periodicity in the spectrum and persistent current as a function of the external flux. 相似文献
17.
《Superlattices and Microstructures》1995,17(2):197-200
A novel planar electron waveguide coupler is proposed as an electronic switch. The structure consists of two quantum wires interconnected by a dual branch coupling scheme which is assumed to be controlled by an electrostatic potential. Switching is provided by tuning the phase relations between the different scattered waves by the two coupling branch lines. Assuming ballistic transport, the analysis is conducted by solving the time independent two-dimensional Schrödinger equation in order to derive the conductance characteristics. At a resonant energy of 25 meV and for a waveguide width of 27.4 nm, over 90% of the electron wave has been transferred with a half picosecond time response. 相似文献
18.
O. Rousière D. Lemoine H. Folliot S. Hinooda R. Granger 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):491-496
Strong oscillations on capacitance and conductance have been observed in p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures, made by using a recent process for the interface passivation. This behaviour is
attributed to a two-dimensional electron gas in the n-inversion layer and the variation of the conductance maximums with temperature
indicates that the dominant perpendicular transport mechanism for electrons is an incoherent two-step tunnelling through deep
levels in the gap. Three models have been used to describe the quantum confinement: the simple variational method, the triangular
potential approximation and the propagation matrix method. The later approach takes into account the non parabolicity of the
conduction band structure and uses a finite height barrier at the insulator-semiconductor interface. A very good agreement
between experimental and calculated values for the two lowest subband energy is obtained.
Received 9 February 1999 相似文献
19.
We theoretically investigate the ballistic conductance of hollow quantum wires made of a two-dimensional electron gas occupying a cylindrical surface. The dependence of the conductance on the electron Fermi momentum differs drastically from the conventional case of a strip-like wire. We trace the evolution between these two cases in an exactly solvable model of a circular cylinder affected by a δ-like potential barrier along its element. We consider also a cylinder with two diametrically opposite δ-function barriers, the case representing somewhat realistic semiconductor structures. The general consequences of the boundary condition topology are also discussed. 相似文献
20.
M.V. Moskalets 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):523-529
The peculiarities of a low temperature heat transfer through a ballistic quantum dot (a double potential barrier) with interacting
leads due to a long-range Coulomb interaction (in the geometrical capacitance approach) are considered. It is found that the
thermal conductance K shows periodic peaks as a function of the electrostatic potential of a dot at low temperatures. At the peak maximum it is
whereas near the minimum it is . Near the peak maximum the dependence K(T) is essentially nonmonotonic at the temperatures correspondent to the level spacing in the quantum dot.
Received 20 October 1999 and Received in final form 20 January 2000 相似文献