Conductance Oscillations through an Aharonov Bohm Ring with a Quantum Gate

Based on a one dimensional quantum wave guide theory, we investigate the ballistic conductance through an Aharonov Bohm ring with a quantum gate. The analytical expression of the conductance is exactly obtained as the function of magnetic flux penetrating the ring and Fermi energy of indcident electrons. When Fermi energy equals that of bound states in the isolated stub, the conductance is fixed at a constant value which is only determined by the geometric structure of the ring system. We have found that there are a new kind of conductance oscillations for some special mesoscopic ring systems. As Fermi energy of incident electrons crosses that of bound state in the isolated stub, the conductance oscillations have no abrupt change of phase by π and are in phase. This striking feature is not in ageement with that of previous experiments and theories. The mechanism causing this new feature is discussed.

Polarized Conductance Oscillations Controlled by Magnetic Field in an Aharonov-Bohm Ring

Oscillations of the spin polarized conductance controlled by a uniform magnetic field in a modified Aharonov Bohm ring is studied with use of one dimensional quantum wave guide. Its expression at zero temperature is obtained as a function of the flux penetrating the ring and the magnetic field. It has been found that there are two kinds of polarized conductance extremas for a given Fermi energy. As Zeemann energy of spin polarized electron in the stub is varied, one kind of extrema exhibits continuous phase shift. However, another is locked at particular values of phase shift and it can only change abruptly from a maxima to a minima when Zeemann crosses the level of the bound state of isolated stub. This is a different mehanism for abrupt change phase of conductance osillations.

Theoretical investigation of frequency characteristics of free oscillation and injection-locked magnetrons

The frequency characteristics of free oscillation magnetron（FOM） and injection-locked magnetron（ILM） are theoretically investigated.By using the equal power voltage obtained from the experiment data,expressions of the frequency and radio frequency（RF） voltage of FOM and ILM,as well as the locking bandwidth,on the anode voltage and magnetic field are derived.With the increase of the anode voltage and the decrease of the magnetic field,the power and its growth rate increase,while the frequency increases and its growth rate decreases.The theoretical frequency and power of FOM agree with the particle-in-cell（PIC） simulation results.Besides,the theoretical trends of the power and frequency with the anode voltage and magnetic field are consistent with the experimental results,which verifies the accuracy of the theory.The theory provides a novel calculation method of frequency characteristics.It can approximately analyze the power and frequency of both FOM and ILM,which promotes the industrial applications of magnetron and microwave energy.

Antiresonance Effect in Electronic Tunnelling through a One-Dimensional Quantum Dot Chain

Electronic tunnelling through a one-dimensional quantum dot chain is theoretically studied, when two leads couple to the individual component quantum dots of the chain arbitrarily. If there are some dangling quantum dots in the chain outside the leads, the electron tunnelling through the quantum dot chain is wholly forbidden while the energy of the incident electron is just equal to the molecular energy levels of the dangling quantum dots, which is known as the antiresonance effect. In addition, the influence of electron interaction on the antiresonance effect is discussed within the Hartree-Fock approximation.