Curvature and Zeeman effects on persistent currents in a multi-walled carbon nanotorus

Taking into account both the intrinsic curvature and Zeeman effects, persistent currents in a multi-walled carbon nanotorus are explored by using a supercell method, within the tight-binding formalism. It is shown that in the absence of the Zeeman effect, the intrinsic curvature induces some dramatic changes in energy spectra and thus changes in the shape of the flux-dependent current. A paramagnetism diamagnetism transition is observed. With consideration of the Zeeman splitting energy, the period of persistent current is destroyed, and a diamagnetism-paramagnetism transition is obtained at high magnetic field. In addition, we further explore the effect of external electric field energy （Eef） on persistent current, indicating that it changes unmonotonously with Eef.

Persistent current in a magnetized Rashba ring

We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spinorbit 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 spinorbit 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.

PERSISTENT CURRENT IN A ONE-DIMENSIONAL MESOSCOPIC RING WITH ELECTRON-PHONON INTERACTION IN THE LATTICE MODEL

A new non-perturbative method is used to discuss the persistent current in a one-dimensional mesoscopic ring threaded by a flux φ with electron-phonon interaction in the lattice model. The current is periodic in φ with a flux quantum φ 0 and the electron-phonon interaction suppresses the persistent current. By considering the contributions of many-phonon correlations, we could obtain more accurate results.

Persistent currents in three-dimensional shell-doped nanorings

The persistent current in three-dimensional （P × N2） nanorings as a function of the unit cell number （P）, the channel number （M =N2）, surface disorder （ζ）, and temperature （T） is theoretically investigated in terms of rotational symmetry. On the whole, the typical current increases linearly with √M but decreases exponentially with P, while wide fluctuations exist therein. In the presence of surface disorder, the persistent current decreases with ζ in the regime of weak disorder but increases in the regime of strong disorder. In addition, it is found that the persistent current in perfect rings decreases exponentially with temperature even at T 〈 T＊, while in most disorder rings, the typical current decreases slightly with temperature at T 〈 T＊.

Fano Interference versus Kondo Effect in Strongly Correlated T-Shaped Quantum Dots Embedded in an Aharonov-Bohm Ring

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.

Aharonov–Casher effect and persistent spin currents in a Coulomb-type potential induced by Lorentz symmetry breaking effects

We investigate quantum effects on a nonrelativistic neutral particle with a permanent magnetic dipole moment that interacts with an electric field.This neutral particle is also under the influence of a background that breaks the Lorentz symmetry.We focus on the Lorentz symmetry violation background determined by a space-like vector field.Then,we show that the effects of the violation of Lorentz symmetry can yield an attractive Coulomb-type potential.Furthermore,we obtain the bound state solutions to the SchrÖdinger–Pauli equation and show that the spectrum of energy is a function of the Aharonov–Casher geometric quantum phase.Finally,we discuss the arising of persistent spin currents.

Persistent spin currents in a triple-terminal quantum ring with three arms

A new model of a triple-terminal quantum ring with three arms is proposed.We develop an equivalent method for reducing the triple-terminal quantum ring to the double-terminal quantum ring and calculate the persistent spin currents in this model.The results indicate that the persistent spin currents show behavior of nonperiodic and unequal amplitude oscillation with increasing semiconductor ring size when the total magnetic flux is zero. However,when the total magnetic flux is non-zero,the persistent spin currents make periodic equal amplitude oscillations with increasing AB magnetic flux intensity.At the same time,the two kinds of spin state persistent spin currents have the same frequency and amplitude but the inverse phase.In addition,the Rashba spin-orbit interaction affects the phase and the phase difference of the persistent spin currents.The average persistent spin currents relate to the arm length and the terminal position as well as the distribution of the magnetic flux in each arm.Furthermore, our results indicate that the AB magnetic flux has different influences on the two kinds of spin state electrons.

Field measurement for superconducting magnets of ADS injector Ⅰ

A superconducting magnet prototype for Accelerator Driven Sub-critical System Injection- I had been designed and fabricated, and tested in a new made vertical Dewar in November 2012. Batch magnet production was processed after some major revision from the magnet prototype, they include： removing off the perm-alloy shield, extending the iron yoke, using thin superconducting wire, etc. The first one of the batch magnets was tested in the vertical Dewar at the Harbin Institute of Technologyin in September 2013. A field measurement was carried out at the same time by the measurement platform that was seated on the top of the vertical Dewar, the measurement results met the design requirements. This paper will present the field measurement system design, measurement results and discussion on the residual field from the persistent current effect.

Review of high temperature superconducting flux pumps

High temperature superconducting(HTS)magnets conduct DC currents ranging from hundreds to tens of thousands of amperes.To achieve such DC output amplitudes,conventional power supplies are unsuitable,owing to their extreme cost,energy consumption,and bulkiness.The indispensable current leads of conventional power supplies carrying large DC current cause an extra heat leakage into the cryogenic system,thus increasing the number of required cryocoolers.A potential solution to tackle this problem,however,is to use HTS flux pumps that inject a large amount of DC current into the HTS magnet in a wireless fashion,thereby eliminating the need for current leads,and allow the magnets to work in the quasi‐persistent current mode.Compared with the conventional power supplies,the flux pumps offer the advantages of low cost,low energy consumption,and compact size,etc.,which essentially have broad application prospects in nuclear magnetic resonance(NMR/MRI),fusion,particle accelerators,superconducting electric machine,maglev train,etc.Over the last decade,a variety of HTS flux pumps have been invented with improved DC outputs,reaching over kiloamperes.Moreover,those flux pumps have different working principles,structures and operation strategies.In this paper,we provide an in‐depth review on the HTS flux pumps developed in the last decade.In particular,for the HTS travelling wave flux pumps and HTS transformer‐rectifier flux pumps,the discussions are focused on their working principles and technical advances.In the end,we discuss the present applications of HTS flux pumps,along with their potential future applications.