Hua Li

The influence of intradot Coulomb interactions on the conductance for a parallel-coupled triple quantum dot system

Using the nonequilibrium Keldysh Green function technique, the influence of intradot Coulomb interactions on conductance for a parallel-coupled triple quantum dot system is investigated. The conductance as a function of electron energy is numerically calculated. The combined effect of the intradot Coulomb interaction and the magnetic flux leads to an intricate conductance lineshape. Moreover, both the magnetic flux and the interdot coupling strength may modulate the Fano effect.

Bistable transmission of antiferromagnetic Fabry-Perot resonator

We investigate the magnetically nonlinear optical transmission of the Fabry-Perot resonator filled with an antiferromagnetic medium. In a proper incident power range, we find very large nonlinear phase shifts so that the bistable switches appear even for a very thin medium film, such as of half-wavelength thickness. All results are based on antiferromagnetic MnF2 medium with far-infrared resonant frequencies.

Magnetostatic surface waves in an FM/LH/FM sandwiched structure

Properties of magnetostatic surface waves in a magnetic structure with one left-handed material (LHM) film sandwiched between two ferromagnetic (FM) films are discussed, where FM films are magnetized to be saturated by an external field parallel to the film surfaces and the LHM film has a constant and negative magnetic permeability. Besides the surface magnetostatic wave lying in the same frequency range as that of a single film, two new branches of surface magnetostatic waves with negative group velocity are found in different frequency ranges. The new branches propagate along the inner surface of an FM film, but the other propagates along the outer surface.

Probing an Individual Electron Spin State in a Quantum Dot with Spin Bias

A quantum dot coupled to two electrodes with spin-dependent splitting of chemical potentials (spin bias) is proposed as a detector of an individual electron spin. Spin polarized transport properties through the quantum dot have been investigated theoretically by means of the nonequilibrium Greens function formalism. We found that the direction of current flow is dependent on the electronic spin state in quantum dot. Measuring the direction of the current flow through the devices, we can determine the direction of the electronic spin state in quantum dot. This proposed detector provides a practical and all electrical approach to detect the electronic spin state in quantum dot structure.

Spin transport through a junction entirely consisting of molecules from first principles

Using first-principles calculations based on density functional theory combined with the nonequilibrium Greens function formalism, we studied the spin transport through a single molecular junction which consists of a single 1,4-benzenedithiolate (BDT) molecule and two ferromagnetic electrodes [(Ge5)Fe]∞. A large magnetoresistance ratio (MR) of 21100% was found in the [(Ge5)Fe]∞-BDT-[(Ge5)Fe]∞ molecular junction at small bias voltage, and the MR value decreased with the increase in the applied bias voltage. For the parallel magnetization configuration, the molecular junction showed outstanding spin injection effects. Negative differential resistance was observed for the antiparallel magnetization configuration. Spin dependent transmission spectra at different bias voltages were used to explain the calculated results.

Spin polarization in a double-quantum dot interferometer with Rashba spin–orbit interaction

We propose a spin device consisting of three normal metal leads and double quantum dots (QDs) with Rashba spin–orbit (RSO) interaction. On the basis of the nonequilibrium Keldysh Greens function technique, the spin-polarized currents flowing in different leads and spin accumulations in QDs are investigated. It is shown that the spin-polarized currents with opposite direction can be extracted into the left and right leads, respectively, due to the quantum interference between different channels. Moreover, the magnitude and direction of polarization can be modulated electrically by shifting the dots’ levels and tuning the strength of the RSO interaction. The spin-polarized currents exhibit a 2π-periodic function with respect to φ R. In addition, the direction of the spin accumulation in two dots is exactly opposite and its magnitude and direction can be easily controlled by tuning the levels.

Nonlinear Far-Infrared Transmission of Antiferromagnetic Fabry-Perot Resonator

The magnetically nonlinear optical transmission of the Fabry-Perot resonator tilled with an antiferromagnetic medium is discussed. In a proper incident power range, we find the bistable switches can appear even for a very thin medium film, such as of half-wavelength thickness. All results are based on antiferromagnetic FeF2 medium with far-infrared resonant frequencies.

Theoretical Study on the Transport through a Quantum Dots Array with a Side Quantum Dot

We studied transport properties through a noninteracting quantum dots array with a side quantum dot employing the equation of motion method and Green function technique. The linear conductance has been calculated numerically. It is shown that an antiresonance always pinned at the energy level of side quantum dot. The conductance develops Fano line shape when the side quantum dot level is not aligned with that of the quantum dots in the array due to quantum interference through different channels.

Effect of Molecular Shape on Polymeric Liquid Crystal

The effect of molecular shape on molecular configuration of liquid crystalline polymers under shear flows is numerically analyzed using the extended Doi theory. We can find that the molecular shape strongly affects on the transition among flow-orientation modes. The change in sign of the first normal stress difference is to speed up by the increasing .

Electronic transport through a T-shaped four-quantum dot system

Making use of the equation of motion method and Keldysh Greens function technique, we have developed a calculation method by which an analytical formula for the current under dc bias is obtained and the transmission probabilities are numerically studied for a T-shaped four-quantum dot (QD) system connected to three terminals. The results are explained in terms of the localization properties of the confined states in the system.