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1.
The possibility of observing persistent voltage in superconducting rings of different arm widths is experimentally investigated. It was previously found that switching of the arms between superconducting and normal states by an AC current induces DC voltage oscillation in the magnetic field with a period corresponding to the flux quantum inside the ring. We used systems with a large number of asymmetric rings connected in series to investigate the possibility of observing this quantum phenomenon near the superconducting transition, where thermal fluctuations lead to switching of ring segments without an external influence and the persistent current is much smaller than in the superconducting state. 相似文献
2.
V. L. Gurtovoi S. V. Dubonos A. V. Nikulov N. N. Osipov V. A. Tulin 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(1):15-19
The current-voltage characteristics and the magnetic field dependences of the critical current have been measured for symmetric and asymmetric superconducting rings and systems of such rings. The dependences obtained explain the periodic change in the rectified voltage observed on asymmetric rings as a result of a periodic change in the asymmetry of current-voltage characteristics. 相似文献
3.
A tunnel current through a heterostructure whose barrier contains quantum rings is calculated. The plane of the rings is parallel to the barrier interface. In a magnetic field perpendicular to this plane, a tunnel current at a fixed bias experiences Aharonov-Bohm oscillations under the variation of magnetic flux through a ring; however, these oscillations are not strictly periodic. 相似文献
4.
W. Y. Cui S. Z. Wu G. Jin X. Zhao Y. Q. Ma 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):47-54
We investigate the electron transmission through a structure of
serial mesoscopic metallic rings coupled to two external leads. A
set of analytical expressions based on the quantum waveguide
transport and the transfer matrix method are derived and used to
discuss the effects of geometric configurations on transmission
probabilities. It is found that in the contact ring case the
existence of an applied magnetic flux is necessary to create
transmission gaps, while in the non-contact ring case transmission
gaps always appear irrespective of whether there is an applied
magnetic flux or not. The transmissions for periodic rings with a
defect ring and periodic rings built by two sorts of rings are
also briefly studied. It is also found that the transmission
periodicity with wave vector must be ensured by the
commensurability of two characteristic lengths, i.e., of the half
perimeter of a ring and the connecting wire between two adjacent
rings. The special points of wave vector and magnetic flux which
give rise to the transmission resonance and antiresonance are
analyzed in detail. 相似文献
5.
6.
M. Solaimani 《Optical and Quantum Electronics》2018,50(7):283
Here, we study the effects of the number of sites, quantum ring radius and potential well depth on the energy levels, persistent current, magnetic susceptibility and density of states (DOS) of a quantum ring with a quantum well within its circumstance in a magnetic flux perpendicular to its plane. We show that, for small radius quantum ring systems, there are periodic local gaps along the magnetic flux axis in the DOS plots and along the axis ‘energy’. For large radius quantum ring systems, a uniform gap along the energy axis exists and along the phi axis nothing changes. In quantum rings with a quantum well in their circumstance, by using the large confining potential, we can create uniform gaps in the Energy–phi plane. The energy eigenvalues, persistent current and magnetic susceptibility decrease by increasing the confining potential. A quantum ring even with a very small confining potential in its circumstance can sensibly decrease the persistent current and magnetic susceptibility, although it may do not change the energy eigenvalues and DOS maximum considerably. Thus, by using the abovementioned parameters, we are able to tune the DOS, persistent current, magnetic susceptibility and energy levels, desirably. 相似文献
7.
M. Himmerich P. G.J. van Dongen R. M. Noack 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):5-15
A nonperturbative method for calculating persistent currents
in molecules and nanoscopic quantum rings is presented. Starting
from the extended Hubbard model on a ring threaded by an
Aharonov-Bohm flux, a feedback term through which the current
can generate magnetic flux is added. Another extension
of the Hamiltonian describes the energy stored in the
internally generated field. This model is evaluated using
exact diagonalization and an iterative scheme to find the
minima of the free energy with respect to the current.
The magnetic properties due to electron delocalization
of conjugated hydrocarbons like
benzene [magnetic anisotropy, magnetic
susceptibility exaltation, nucleus-independent
chemical shift (NICS)] — that have become important
criteria for aromaticity — can be examined using this model.
A possible novel mechanism for a permanent orbital magnetic moment
in quantum rings analogous to the one in π-SQUIDs is found in the
framework of the proposed model. The quantum rings must
satisfy two conditions to exhibit this kind of
permanent orbital magnetic moment: a negative
Drude weight and an inductivity
above the critical level. 相似文献
8.
A. A. Burlakov V. L. Gurtovoi A. I. Il’in A. V. Nikulov V. A. Tulin 《JETP Letters》2014,99(3):169-173
A new type of a superconducting quantum interference device (SQUID) based on a single superconducting loop without Josephson junctions and with asymmetric contacts has been proposed. This SQUID offers advantages in simplicity of fabrication and a steeper dependence of measured quantities on the magnetic flux. To confirm the possibility of making this type of SQUID, the magnetic field dependence of the critical current in an aluminum ring with asymmetric contacts has been experimentally investigated. 相似文献
9.
É. V. Matizen P. P. Bezverkhii V. G. Martynets 《Journal of Experimental and Theoretical Physics》1997,84(3):578-583
We establish how trapped magnetic flux depends on the frequency and amplitude of an alternating field and how such a field
affects the relaxation rate of the flux. We find that the nature of the flux creep changes in the process and that relaxation
of the flux stops after the external field is switched off. We examine the dynamics of flux relaxation in a ring in the approximation
in which the current density is assumed homogeneous, for various density dependences of the effective vortex activation energy.
The critical current density and the vortex activation energy are obtained as functions of the external field strength. Finally,
we explain the observed behavior in terms of the different field profiles emerging in the rings.
Zh. éksp. Teor. Fiz. 111, 1047–1056 (March 1997) 相似文献
10.
V. I. Kuznetsov A. A. Firsov S. V. Dubonos M. V. Chukalina 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(8):1083-1085
The interaction between the quantum states of two circularly asymmetric superconducting aluminum rings forming figure eight, threaded by a magnetic flux and biased by an external sinusoidal ac current with zero dc component, has been investigated. Quantum oscillations in the dependence V dc(B) of the rectified dc voltage on magnetic field for these structures have been measured at different external currents and temperatures close to critical. Fourier and wavelet analyses of the function V dc(B) have revealed, along with the two fundamental ring frequencies, various combination frequencies; this fact is indicative of interaction in the structure. Deviation of the function V dc(B) from oddness with respect to the magnetic field direction has been found for the first time. 相似文献
11.
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
12.
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
13.
G. Q. Zha 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(3):459-466
The magnetic flux dependence of the vortex state for small mesoscopic superconducting
rings surrounded by a medium is investigated by the phenomenological Ginzburg-Landau
theory. The influences of the ring size and the surface superconductivity on the free
energy and total supercurrent are studied. For narrow rings, the persistent current
evolves towards a periodic behaviour with magnetic flux. The complete paramagnetic or
diamagnetic state, corresponding to positive or negative current flowing in the whole
ring, can occur. A remarkable intermittent superconducting behaviour for the ground-state
transition is found when the strength of surface-suppressed superconductivity is enlarged
or the ring size is decreased. Consequently, a pure superconducting state with positive
total current can be obtained. 相似文献
14.
Effect of electric field on the electronic spectrum and the persistent current of a quantum ring with two electrons 总被引:1,自引:0,他引:1
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The effect of an electric field E on a narrow quantum ring that contains two
electrons and is threaded by a magnetic flux B has been investigated. Localization
of the electronic distribution and suppression of the Aharonov--Bohm oscillation
(ABO) are found in the two-electron ring, which are similar to those found in a
one-electron ring. However, the period of ABO in a two-electron ring is reduced by
half compared with that in a one-electron ring. Furthermore, during the variation of
B, the persistent current of the ground state may undergo a sudden change in sign.
This change is associated with a singlet--triplet transition and has no counterpart
in one-electron rings. For a given E, there exists a threshold of energy. When
the energy of the excited state exceeds the threshold, the localization would
disappear and the ABO would recover. The value of the threshold is proportional to
the magnitude of E. Once the threshold is exceeded, the persistent current is much
stronger than the current of the ground state at E=0. 相似文献
15.
当前行波管周期永磁聚焦系统的波端口位置处的磁环通常采用单向开口磁环。在波端口位置引入波导阻抗调谐支节的基础上,提出了两种不同的双向开口磁环结构。利用三维电磁仿真软件Opera-3D,分析了双开口磁环的中心轴线附近的磁场,并据此进一步介绍了带双开口磁环周期永磁聚焦系统的设计方法。为了验证带双开口磁环的周期永磁聚焦系统应用的可行性,设计和测试了一套E波段折叠波导行波管电子光学系统。在行波管试验中,电子枪发射电流83 mA,带双开口磁环的周期永磁聚焦系统聚焦的电子束流通率达到99%。 相似文献
16.
V. L. Gurtovoi S. V. Dubonos A. V. Nikulov N. N. Osipov V. A. Tulin 《Journal of Experimental and Theoretical Physics》2007,105(6):1157-1173
The obtained periodic magnetic-field dependences I c+(Φ/Φ0) and I c?(Φ/Φ0) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I c?(Φ/Φ0) = I c+(Φ/Φ0 + Δ?) of the critical current measured in opposite directions. This shift means that the position of I c+(Φ/Φ0) and I c?(Φ/Φ0) minima does not correspond to n + 0.5 magnetic flux Φ quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I c, an(Φ/Φ0) = I c+(Φ/Φ0) ? I c?(Φ/Φ0) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature. 相似文献
17.
18.
Barash YS 《Physical review letters》2008,100(17):177003
Wave functions of low-energy quasiparticle subgap states in d-wave superconducting rings, threaded by an Aharonov-Bohm magnetic flux, are found analytically. The respective energies are closest to the midgap position at small magnetic fluxes and deviate from the Fermi surface due to the Doppler shift, produced by the supercurrent. The Doppler-shifted zero-energy states result in a paramagnetic response of the ring at small fluxes. The states exist only for even angular momenta of the center of mass of Cooper pairs, in agreement with recent numerical studies of the problem. This macroscopic quantum effect in d-wave rings results in broken h/2e periodicity, retaining only the h/e periodic behavior of the supercurrent with varying magnetic flux. 相似文献
19.
研究了与铁磁/半导体/铁磁结构相关的双量子环自旋输运的规律,研究结果表明:总磁通为零条件下,铁磁电极磁化方向反平行时,双量子环与单量子环相比提高了自旋电子透射概率的平均值.铁磁电极磁化方向平行时,双量子环对提高自旋向下电子平均透射概率的效果更明显;双量子环受到Rashba自旋轨道耦合作用影响时,自旋电子的平均透射概率明显高于单量子环,即使再加上外加磁场的影响,透射概率较高这一特征依然存在;双量子环所含的δ势垒具有阻碍自旋电子输运的作用,随δ势垒强度Z的增大透射概率
关键词:
双量子环
Rashba自旋轨道耦合
透射概率
δ势垒')" href="#">δ势垒 相似文献
20.
Ying-hua Ji Hai-mei Luo Jie Liu Hua-Ming Wan 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):668-674
We propose a quantum Hamiltonian and obtain the relationship between external magnetic field and currents of three mesoscopic coupling rings. The impact of coupling on quantum current magnification in the system is studied. It is found that the quantum current magnification effect strongly depend on both the external magnetic flux and the coupling factors. As a result, by taking use of coupling rings, we can design some circuits to transfer and communicate signals. 相似文献