共查询到20条相似文献,搜索用时 46 毫秒
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M.V. Moskalets 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):645-649
The effect of an electrostatic energy (in the geometrical capacitance approach) on a persistent current is considered. It
is shown that at high temperatures the current amplitude shows periodic dips as a function of the potential difference between
a ring and a reservoir. These dips correspond to a lift of the Coulomb blockade. In a minimum of a dips a current is periodic
in a magnetic flux with a period at any temperatures.
Received: 6 April 1998 / Revised: 5 June 1998 / Accepted: 21 July 1998 相似文献
3.
We study persistent currents in the double Aharonov-Bohm ring connected to two electron reservoirs by quantum waveguide theory. It is found that the persistent currents in the double Aharonov-Bohm ring depend on the direction of the current flow from one reservoir to another. When the direction of the current flow reverses, the persistent current in each ring of the double Aharonov-Bohm ring changes. If the two rings are of the same size, the persistent currents in the left and the right rings exchange at the reversal of the current flow direction. 相似文献
4.
Persistent current and transmission probability in the Aharonov-Bohm (AB) ring with an embedded quantum dot (QD) are studied using the technique of the scattering matrix. For the first time, we find that the persistent current can arise in the absence of magnetic flux in the ring with an embedded QD. The persistent current and the transmission probability are sensitive to the lead-ring coupling and the short-range potential barrier. It is shown that increasing the lead-ring coupling or the short-range potential barrier causes the suppression of the persistent current and the increasing resonance width of the transmission probability. The effect of the potential barrier on the number of the transmission peaks is also investigated. The dependence of the persistent current and the transmission probability on the magnetic flux exhibits a periodic property with period of the flux quantum. 相似文献
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The ground state of a phase-coherent mesoscopic system is sensitive to its environment. We investigate the persistent current of a ring with a quantum dot which is capacitively coupled to an external circuit with a dissipative impedance. At zero temperature, zero-point quantum fluctuations lead to a strong suppression of the persistent current with decreasing external impedance. We emphasize the role of displacement currents in the dynamical fluctuations of the persistent current and show that with decreasing external impedance the fluctuations exceed the average persistent current. 相似文献
7.
The present work is dedicated to the time evolution of excitation of a quantum ring in external electric and magnetic fields. Such a ring of mesoscopic dimensions in an external magnetic field is known to exhibit a wide variety of interesting physical phenomena. We have studied the dynamics of the single electron quantum ring in the presence of a static magnetic field and a combination of delayed half-cycle pulse pair. Detailed calculations have been worked out and the impact on dynamics by variation in the ring radius, intensity of external electric field, delay between the two pulses, and variation in magnetic field have been reported. A total of 19 states have been taken and the population transfer in the single electron quantum ring is studied by solving the time-dependent Schrödinger equation (TDSE), using the efficient fourth-order Runge–Kutta method. Many interesting features have been observed in the transition probabilities with the variation of magnetic field, delay between pulses and ring dimensions. A very important aspect of the present work is the persistent current generation in a quantum ring in the presence of external magnetic flux and its periodic variation with the magnetic flux, ring dimensions and pulse delay. 相似文献
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We investigate the equilibrium property of a mesoscopic ring with a spin-orbit interaction. It is well known that, for a normal mesoscopic ring threaded by a magnetic flux, the electron acquires a Berry phase that induces the persistent (charge) current. Similarly, the spin of an electron acquires a spin Berry phase traversing a ring with a spin-orbit interaction. It is this spin Berry phase that induces a persistent spin current. To demonstrate its existence, we calculate the persistent spin current without an accompanying charge current in the normal region in a hybrid mesoscopic ring. We point out that this persistent spin current describes the real spin motion and can be observed experimentally. 相似文献
10.
M. Henkel D. Karevski 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):787-792
The effect of point defects on persistent currents in mesoscopic rings is studied in a simple tight-binding model. Using an
analogy with the treatment of the critical quantum Ising chain with defects, conformal invariance techniques are employed
to relate the persistent current amplitude to the Hamiltonian spectrum just above the Fermi energy. From this, the dependence
of the current on the magnetic flux is found exactly for a ring with one or two point defects. The effect of an aperiodic
modulation of the ring, generated through a binary substitution sequence, on the persistent current is also studied. The flux-dependence
of the current is found to vary remarkably between the Fibonacci and the Thue-Morse sequences.
Received: 4 March 1998 / Revised: 20 April 1998 / Accepted: 30 April 1998 相似文献
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P. Kopietz A. Völker 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):397-405
A time-dependent electric field gives rise to a stationary non-equilibrium current I
(2)
around a mesoscopic metal ring threaded by a magnetic flux. We show that this current, which is proportional to the intensity
of the field, is closely related to the exchange part of the interaction contribution to the equilibrium persistent current, and that the corresponding non-linear conductivity directly measures the weak localization correction
to the polarization. We explicitly calculate the disorder average of I
(2)
in the diffusive regime as function of the frequency of the electric field and the static flux piercing the ring, and suggest
an experiment to test our theory.
Received: 5 September 1997 / Accepted: 4 November 1997 相似文献
13.
The persistent current in the ground state of a quantum ring threaded by a magnetic flux is calculated within the framework of the Holstein-Hubbard model. It is found that the persistent current is suppressed by both the electron–electron and electron–phonon interactions. Calculation of Drude weight reveals that the persistent current is diamagnetic in nature. It is observed that as the number of atoms in the quantum ring increases, the persistent current decays in a continuous way. It is finally predicted that there exists an intervening metallic phase flanked in real time by two insulating phases, the SDW phase and the CDW phase. 相似文献
14.
A. H. Phillips N. A. I. Aly K. Kirah H. E. El-Sayes 《中国物理快报》2008,25(1):250-253
The transport property of a quantum dot under the influence of external time-dependent field is investigated. The mesoscopic device is modelled as semiconductor quantum dot coupled weakly to superconducting leads via asymmetric double tunnel barriers of different heights. An expression for the current is deduced by using the Landauer-Buttiker formula, taking into consideration of both the Coulomb blockade effect and the magnetic field. It is found that the periodic oscillation of the current with the magnetic field is controlled by the ratio of the frequency of the applied ac-field to the electron cyclotron frequency. Our results show that the present device operates as a radio-frequency single electron transistor. 相似文献
15.
Within the framework of the effective mass approximation, coherent oscillations of a photoexcited electron wave packet in an asymmetric coupled quantum well structure have been studied using a time-dependent Schrödinger equation. In the method of calculation, the continuity of the current across a semiconductor heterojunction is considered. The amplitude and period of the electronic is obtained and in the case of high bias, it is found the existence of electric field-induced tunelling to semiconductor bulk. 相似文献
16.
We give a rigorous (Hamiltonian) treatment of a quantum system weakly coupled to an infinite free reservoir and subject to an external time-dependent driving potential varying on the scale of dissipation. The linear response of the system initially in thermal equilibrium is determined and compared with the usual expressions of linear response theory.Work partly supported by NSF grant no. MPS 75-11864-A04.On leave of absence from Fachbereich Physik der Universität München. Work supported by a DFG fellowship. 相似文献
17.
We present an implementation of a new method for explicit simulations of time-dependent electric currents through nanojunctions. The method is based on unitary propagation of stroboscopic wave packet states and is designed to treat open systems with fluctuating number of electrons while preserving full quantum coherence throughout the whole infinite system. We demonstrate the performance of the method on a model system consisting of a ring-shaped nanojunction with two semi-infinite tight-binding leads. Time-dependent electron current responses to abrupt bias turn-on or gate potential switching are computed for several ring configurations and ring-leads coupling parameters. The found current-carrying stationary states agree well with the predictions of the Landauer formula. As examples of genuinely time-dependent process we explore the presence of circulating currents in the rings in transient regimes and the effect of a time-dependent gate potential. 相似文献
18.
Spin-polarization-dependent transport in a quantum dot array coupled with an Aharonov-Bohm ring
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In this paper the quantum transport in a dot-array coupled with an Aharonov–Bohm (AB) ring is investigated via single-band tight-binding Hamiltonian. It is shown that the output spin current is a periodic function of the magnetic flux in the quantum unit Φ0. The resonance positions of the total transmission probability do not depend on the size of the AB ring but the electronic spectrum. Moreover, the persistent currents in the AB ring is also spin-polarization dependent and different from the isolated AB ring where the persistent current is independent of spin polarization. 相似文献
19.
Fano Interference versus Kondo Effect in Strongly Correlated T-Shaped Quantum Dots Embedded in an Aharonov-Bohm Ring
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We theoretically investigate the properties of the ground state of the strongly correlated T-shaped double quantum dots embedded in an Aharonov-Bohm ring in the Kondo regime by means of the one-impurity Anderson Hamiltonian. It is found that in this system, the persistent current depends sensitively on the parity and size of the ring. With the increase of interdot coupling, the persistent current is suppressed due to the enhancing Fano interference weakening the Kondo effect. Moreover, when the spin of quantum dot embedded in the Aharonov- Bohm ring is screened, the persistent current peak is not affected by interdot coupling. Thus this model may be a new candidate for detecting Kondo screening cloud. 相似文献
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We report a theoretical study on producing electrically spin-polarized current in the Rashba ring with parallel double dots embedded, which are subject to two time-dependent microwave fields. By means of the Keldysh Green's function method, we present an analytic result of the pumped current at adiabatic limit and demonstrate that the interplay between the quantum pumping effectand spin-dependent quantum interference can lead to an arbitrarily controllable spin-polarized current in the device. The magnitude and direction of the charge and spin current can be effectively modulated by system parameters such as the pumping phase difference, Rashba precession phase, and the dynamic phase difference of electron traveling in two arms of ring; moreover, thespin-polarization degree of the charge current can also be tuned in the range [-∞, +∞]. Our findings may shed light on the all-electric way to produce the controllable spin-polarized charge current in the field of spintronics. 相似文献