Quantum phase transitions in mesoscopic Rashba rings

Novel quantum phases are found in the ground state of Rashba ring: the orbital magnetic phase (OMP), non-OMP, pseudo-OMP and quasi-OMP, which depend on the spin-orbit interaction (SOI) strength, electron number and ring size. We give the phase diagram and their quantum-phase-transition conditions.     

Spin-orbit coupling and spin current in mesoscopic devices

Recently,the spin-orbit coupling and spin current in nanodevice have been investigated extensively.In this paper,we review the recent progresses in this field.We introduce the real space Hamiltonian and the second quantization Hamiltonian of a typical quantum transport mesoscopic device,metal-QD-metal configuration,containing the spin-orbit interaction,e-e interactions,and magnetic field.Some noteworthy effects(e.g.,the spin-polarized current,spin accumulation,persistent spin current) originated from the spin-orbit interaction are reviewed,and the electric field induced by spin-current is mentioned.Lastly,we introduce some unsolved problems and prospects in this field.     

Persistent currents in mesoscopic rings

The discrepancy between measured values of the persistent current in mesoscopic rings and theoretical calculations based upon the model of independent electrons moving in a random potential is discussed. Some attempts at including the Coulomb interaction between electrons are reviewed, and results of model calculations are presented.     

Interference and interactions in mesoscopic rings

We consider a mesoscopic ring connected to external reservoirs by tunnel junctions. The ring is capacitively coupled to an external gate electrode and may be pierced by a magnetic field. Due to strong electron–electron interactions within the ring the conductance shows Coulomb blockade oscillations as a function of the gate voltage, while Aharonov–Bohm interference effects lead to a dependence on the magnetic flux. The Hamiltonian of the ring is given by a Luttinger model that allows for an exact treatment of both interaction and interference effects. We conclude that the positions of conductance maxima as a function the external parameters can be used to determine the interaction parameter , and the shapes of conductance peaks are strongly affected by electron correlations within the ring.     

介观薄圆环中的间隙性超导

本文运用了唯象的Ginzburg-Landau 理论研究了介观薄圆环的间隙性超导, 给出了在外磁场作用下超导圆环出现间隙性超导现象的尺寸相图. 这种间隙性超导现象只出现在尺寸小圆环中, 而且是超导圆环区别于超导圆盘的一个特征.     

Intermittent superconductivity in three-dimensional mesoscopic rings

Three-dimensional mesoscopic rings are investigated by the phenomenological Ginzburg–Landau theory in the presence of an externally applied magnetic-field. By solving an eigenvalue problem and minimizing systematic free energy, we find that the superconducting and normal states cyclically appear, and that between the state L and the state L + 1 the field extent of existing normal state increases with increase of vorticity L. The dimensional phase diagram with the maximum vorticity and existing normal state between two superconducting states is given. The normal state can be controlled by the medium with surface enhancement or suppression of superconductivity.     

Persistent currents in mesoscopic connected rings

We report measurements of the low temperature magnetic response of a line of 16 GaAs/GaAlAs connected mesoscopic rings whose total length is much larger than l(straight phi). Using an on-chip micro-SQUID technology, we have measured a periodic response, with period h/e, corresponding to persistent currents in the rings of a typical amplitude of 0.40+/-0.08 nA per ring. Direct comparison with measurements on the same rings but isolated is presented.     

Photoinduced charge currents in mesoscopic rings

The temporal and spatial controllability of charge distribution in submicron structures opens new avenues for potential applications and for the understanding of nonequilibrium processes. Here we suggest a novel way to trigger and control within picoseconds charge currents and magnetic moments in nanoscopic and mesoscopic ring structures by applying two shaped, time-delayed light pulses. Our quantum dynamic calculations show that the magnitude and direction of the induced currents are tunable by varying the time delay and strengths of the pulses. Furthermore, in an array of rings desirable magnetic orders are generated depending on the ring sizes and particle number.