Adel H. Phillips

Spin Polarized Transport in an AC-Driven Quantum Curved Nanowire

Using the effective-mass approximation method, and Floquet theory, we study the spin transport characteristics through a curved quantum nanowire. The spin polarization, 𝑃 , and the tunneling magnetoresistance, TMR, are deduced under the effect of microwave and infrared radiations of wide range of frequencies. The results show an oscillatory behavior of both the spin polarization and the tunneling magnetoresistance. This is due to Fano-type resonance and the interplay between the strength of spin-orbit coupling and the photons in the subbands of the one-dimensional nanowire. The present results show that this investigation is very important, and the present device might be used to be a sensor for small strain in semiconductor nanostructures and photodetector.

Photo-Induced Spin Dynamics in Nanoelectronic Devices

The present research is devoted to the investigation of electron spin transmission through a nanoelectronic device. This device is modeled as nonmagnetic semiconductor quantum dot coupled to two diluted magnetic semiconductor leads. The spin transport characteristics through such a device are investigated under the effect of an ac-field of a wide range of frequencies. The present result shows a periodic oscillation of the conductance for both the cases of parallel and antiparallel spin alignment. These oscillations are due to Fano-resonance. Results for spin polarization and giant magneto-resistance show the coherency property. The present research might be useful for developing single spin-based quantum bits (qubits) required for quantum information processing and quantum spin-telecommunication.

SPIN-COHERENT TRANSPORT IN MESOSCOPIC INTERFERENCE DEVICE

We investigate the quantum size effect in the phase coherent mesoscopic ring. A quantum dot is embedded in one arm and it is connected to one lead via tunnel barrier. Both Aharonov–Casher and Aharonov–Bohm effects are studied. A spin-dependent conductance has been deduced and it depends on the intrinsic parameters. Our results show that the strength of spin-orbit coupling depends on the size of the present device. This investigation is valuable for fabricating such spintronics devices.

ELECTRON SPIN DYNAMICS THROUGH FERROMAGNETIC QUANTUM POINT CONTACT

We study spin-dependent tunneling through ferromagnetic quantum point contact. It was found that both the current and the conductance show increasing oscillatory fluctuations with the variation of Fermi energy and contact area at different temperatures. These oscillations are due to polarization inversion at the incoming of each new sub-band and increasing transmission probability through the higher sub-bands. The results are found to be in good concordance with those in the literature.

STUDY OF THE ANOMALY PHENOMENA FOR THE HYBRID SUPERCONDUCTOR-SEMICONDUCTOR JUNCTIONS

The conductance anomaly behavior for superconductor-semiconductor-superconductor junctions is investigated. We propose a potential profile at the interface which depends on the intrinsic parameters of the junctions, e.g. carrier concentration. The tunneling probability is derived by the WKB method and the corresponding conductance is expressed in terms of the tunneling probability through Landauer–Buttiker formula. The results show a zero-bias anomaly (ZBA) for the dependence of conductance on bias voltage. Also, the oscillatory behavior of the conductance with the magnetic field, due to the chaotic behavior of the junction.

Simulation of the Band Structure of Graphene and Carbon Nanotube

Simulation technique has been performed to simulate the band structure of both graphene and carbon nanotube. Accordingly, the dispersion relations for graphene and carbon nanotube are deduced analytically, using the tight binding model & LCAO scheme. The results from the simulation of the dispersion relation of both graphene and carbon nanotube were found to be consistent with those in the literature which indicates the correctness of the process of simulation technique. The present research is very important for tailoring graphene and carbon nanotube with specific band structure, in order to satisfy the required electronic properties of them.

PHOTON-ASSISTED TRANSPORT IN CARBON NANOTUBE MESOSCOPIC DEVICE

The aim of the present paper is to investigate the quantum transport properties of a mesoscopic device under the influence of gate voltage and photon energy. A model for such mesoscopic devices is proposed as two metal contacts are deposited on the carbon nanotube quantum dot to serve as source and drain electrodes. The conducting substrate is the gate electrode in this three-terminal mesoscopic device. Another metallic gate is used to govern the electrostatics and the switching of carbon nanotube channel. The substrate at the carbon nanotube quantum dot contacts are controlled by the back gate. Both effects of the photons energy and gate voltage are investigated. The photon-assisted tunneling probability is deduced by solving Dirac equation. Then the current is deduced according to Landauer–Buttiker formula. The quantum capacitance for the device is deduced in terms of density of states. Oscillatory behavior of the current is observed which is due to the Coulomb blockade oscillations. It was found, also, that the peak heights of the dependence of the current on the parameters under study are strongly affected by the interplay between the tunneled electrons and the photon energy. This interplay affects the sidebands resonance. The results obtained in this study are found to be in concordant with those in the literature, which confirm the correctness of the proposed model. This study is valuable for nanotechnology applications, e.g., photodetector devices and solid state quantum computing systems and quantum information processes.

Thermal Shot Noise through Boundary Roughness of Carbon Nanotube Quantum Dots

Thermal shot noise, thermal voltage and thermo power are studied through a carbon nanotube quantum dot coupled to two leads with random roughness of amplitude on each of the two boundaries, under the effect of microwave field, and magnetic field. The expressions for the thermal shot noise and thermal energy are deduced when the barrier strength and contact area are taken into consideration. A model for such mesoscopic devices is proposed as a carbon nanotube quantum dot coupled to two leads with random roughness of amplitude on each of the two boundaries. The results show oscillatory behaviors of the dependence of the thermal shot noise on the studied parameters. The thermopower oscillates with the variation of the contact area, and the peak heights decrease linearly with the contact area and increases with temperature. This trend of behavior is due to the interplay of the induced microwave photons and the tunneling rate through the side bands. This research is important for using a model as a high-frequency shot noise detector and the thermopower is sensitive to the energy dependence of the conductance.

Transport Characteristics of Mesoscopic Radio-Frequency Single Electron Transistor

The transport property of a quantum dot under the influence of external time-dependent field is investigated. The mesoscopic device is modelled as semiconductor quantum dot coupled weakly to superconducting leads via asymmetric double tunnel barriers of different heights. An expression for the current is deduced by using the Landauer–Buttiker formula, taking into consideration of both the Coulomb blockade effect and the magnetic field. It is found that the periodic oscillation of the current with the magnetic field is controlled by the ratio of the frequency of the applied ac-field to the electron cyclotron frequency. Our results show that the present device operates as a radio-frequency single electron transistor.

Thermodynamics Properties of Mesoscopic Quantum Nanowire Devices

We investigate the thermodynamics properties of mesoscopic quantum nanowire devices, such as the effect of electron-phonon relaxation time, Peltier coefficient, carrier concentration, frequency of this field, and channel width. The influence of time-varying fields on the transport through such device has been taken into consideration. This device is modelled as nanowires connecting to two reservoirs. The two-dimensional electron gas in a GaAs–AlGaAs heterojunction has a Fermi wave length which is a hundred times larger than that in a metal. The results show the oscillatory behaviour of dependence of the thermo power on frequency of the induced field. These results agree with the existing experiments and may be important for electronic nanodevices.