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We consider a microscopic model for a one-dimensional ring of non-interacting electrons threaded by a magnetic flux of the form Φ(t)=Φ0+Φ1cos(Ω0t). The ring is attached to two reservoirs at which a bias voltage is applied. We focus on small amplitudes of Φ1, and we analyze the behavior of the conductance as a function of Φ0. We solve the problem by means of non-equilibrium Green function techniques. 相似文献
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Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
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We have investigated the quantum transport through mesoscopic systems with a toroidal carbon nanotube coupled with two metal leads (N-TCN-N) threaded with an ac magnetic flux. The energy shifting takes place by applying the magnetic flux, and this shifting arises from both the dc and ac components of magnetic flux. The dc magnetic flux
induces the periodic variation of energy gap E
g
of the TCN, and the ac magnetic flux component always increases the energy gap. As the photon energy is larger than the energy gap
, the electrons in the valence band can jump to the conductance band at zero temperature, and the tunneling current appears for
, (
). The differential conductance and tunneling current display clear effect of ac flux by modifying the current oscillation structures. The photon-assisted tunneling current exhibits stair-like I-V characteristics, and it shows different behaviors for different TCN systems. The magnitude of the current is suppressed by the applied ac flux. We also present the time-dependent current evolution, which is contributed by the oscillating current components.Received: 31 May 2004, Published online: 3 August 2004PACS:
73.40.-c Electronic transport in interface structures - 73.63.Fg Nanotubes - 73.61.Wp Fullerenes and related materials - 73.22.-f Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals 相似文献
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L.G. Wang 《Physica B: Condensed Matter》2009,404(1):143-145
The transport property of electron in a quantum ring-stub system is investigated through quantum waveguide theory. The persistent current is produced and controlled by tuning the length of the stub even in the absence of the magnetic field, and it can be observed if one tuning the Fermi energy near the antiresonance or the Fano resonance of the transport current. 相似文献
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We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spin-orbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spin-orbit interaction. Because of broken time reversal symmetry, the two oppositely flowing spin-up and spin-down charge currents of the equilibrium spin current are no longer equal, and so a net persistent charge current can flow in the system. It is also found that the persistent current can be modulated by the Fermi energy, the Rashba spin-orbit interaction strength and the magnetization in the ring. Moreover, the magnetization perpendicular to the ring plane can optimize the current. The persistent current flowing in the ring is a manifestation of the nonzero equilibrium spin current existing in the ring. 相似文献
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We explore the surface disorder effect on the persistent current in a finite-width ring. In the strong disorder regime, the persistent current increases with surface disorder strength, while it decreases in the weak disorder regime. The result is at variance with the observation in bulk-disordered ring. Also, it is shown that the disorder-induced changes in the persistent current strongly depend on both the ring width and radius, which show up a singular quantum size effect. 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
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《Superlattices and Microstructures》1998,23(2):485-488
We calculate the persistent current in a multichannel semiconductor ring with strongly correlated electrons when they form a Wigner crystal (WC). Pinning this crystal with a smooth gate potential leads to the suppression of the amplitude of the Aharonov–Bohm oscillations and to the fractionalization of the period. A fractional period Φ0/w (w = 2,3,…,6) appears because of the strong coupling between channels in the tunneling process of the WC through the pinning barrier. 相似文献
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A.A. Zvyagin 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):351-360
The behavior of charge and spin persistent currents in an integrable lattice ring of strongly correlated electrons with a
magnetic impurity is exactly studied. Our results manifest that the oscillations of charge and spin persistent currents are
similar to the ones, earlier obtained for integrable continuum models with a magnetic impurity. The difference is due to two
(instead of one) Fermi velocities of low-lying excitations. The form of oscillations in the ground state is “saw-tooth”-like,
generic for any multi-particle coherent one-dimensional models. The integrable magnetic impurity introduces net charge and
spin chiralities in the generic integrable lattice system, which determine the initial phase shifts of charge and spin persistent
currents. We show that the magnitude of the charge persistent current in the generic Kondo situation does not depend on the
parameters of the magnetic impurity, unlike the (magneto)resistivity of transport currents.
Received 30 January 2003 / Received in final form 12 March 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: zvyagin@fy.chalmers.se 相似文献
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Zeitschrift für Physik B Condensed Matter - Effects of the Aharonov-Bohm flux on soliton excitations in the molecular-crystal model with the dispersion term in a one-dimensional ring are... 相似文献
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C.M. Falco 《Solid State Communications》1976,19(7):623-625
The thermally induced magnetic flux in a bi-metallic superconducting loop of Nb and Ta has been measured and compared with theory. The predicted logarithmic divergence of the flux near the Tc of Ta is found, however the magnitude of the flux is larger than predicted. 相似文献
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Hong-Kang Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):365-372
The ac Stark effect is investigated in the toroidal carbon nanotube system threaded with an ac magnetic flux. The Floquet
theory is employed to deal with the time-dependent quantum problems. The time-averaged energy of the system is derived and
is found to exhibit a strong relationship with an external field, and the modified energy gap has been presented. The ac flux
enhances energy gaps to cause metal-semiconductor transition. The steady current has been obtained by employing the free energy
approach, and the persistent current is a special case as the magnitude of the ac flux approaches zero. The photon-assisted
current is quite different from the persistent current due to the absorption and emission of photons. The local density of
states is obtained by calculating the Green's function in the Floquet state, and photon-resonant structures are observed.
All of the novel features are associated with the ac Stark effect, which is caused by the modification of energy levels.
Received 20 November 2002 / Received in final form 7 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: zhaohonk@yahoo.com 相似文献
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首次提出了利用周期永磁环做初始能源的螺旋型爆磁压缩发生器,该结构由4节永磁环正反排到组成。阐述了这种周期永磁环爆磁压缩发生器的结构及其特点,并利用等效电路模型分析了轴线起爆周期永磁环爆磁压缩发生器的磁通变化规律和爆磁压缩过程,得到了基本的电流变化关系。 分析及数值计算结果表明:这种周期永磁环爆磁压缩发生器能够实现电流放大,在磁化电流为0.13 MA,磁化回路负载电感为1.0 μH条件下,最终输出电流可达0.16 MA。周期永磁环可以作为爆磁压缩发生器的初始能源,这种概念设计值得进行进一步的实验探索。 相似文献
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首次提出了利用周期永磁环做初始能源的螺旋型爆磁压缩发生器,该结构由4节永磁环正反排到组成。阐述了这种周期永磁环爆磁压缩发生器的结构及其特点,并利用等效电路模型分析了轴线起爆周期永磁环爆磁压缩发生器的磁通变化规律和爆磁压缩过程,得到了基本的电流变化关系。 分析及数值计算结果表明:这种周期永磁环爆磁压缩发生器能够实现电流放大,在磁化电流为0.13 MA,磁化回路负载电感为1.0 μH条件下,最终输出电流可达0.16 MA。周期永磁环可以作为爆磁压缩发生器的初始能源,这种概念设计值得进行进一步的实验探索。 相似文献
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We calculate the average persistent current in a normal conducting, mesoscopic ring in the diffusive regime. In the presence of magnetic impurities, a contribution to the persistent current is identified, which is related to fluctuations in the electron spin density. Assuming a spin-flip scattering rate which is comparable to the Thouless energy E c and low temperature, this new contribution to the persistent current is of the order I ~ E c 2 (kTφ0), which is considerably larger than the persistent current induced by the electron-electron interaction. 相似文献