N. Porras-Montenegro

Laser-dressing effects on the electron g factor in low-dimensional semiconductor systems under applied magnetic fields

The effects of a laser field on the conduction-electron effective Land? g factor in GaAs?Ga1?xAlxAs quantum wells and quantum-well wires under applied magnetic fields are studied within the effective-mass approximation. The interaction between the laser field and the semiconductor heterostructure is taken into account via a renormalization of the semiconductor energy gap and conduction-electron effective mass. Calculations are performed for the conduction-electron Land? factor and g-factor anisotropy by considering the non-parabolicity and anisotropy of the conduction band. Theoretical results are obtained as functions of the laser intensity, detuning and geometrical parameters of the low-dimensional semiconductor heterostructures, and indicate the possibility of manipulating and tuning the conduction-electron g factor in heterostructures by changing the detuning and laser-field intensity.

Zero-(n) non-Bragg gap plasmon-polariton modes and omni-reflectance in 1D metamaterial photonic superlattices.

A theoretical study of the photonic band structure and transmission spectra for 1D periodic superlattices with an elementary cell composed of two layers of refractive indices n(a) and n(b), which may take on positive as well as negative values, has been performed within the transfer-matrix approach. The dependence on the angle of incidence of the electromagnetic wave for excitation of plasmon-polaritons as well as the properties of the (n) = 0 gap were thoroughly investigated. Results are found for the generalized conditions that must be satisfied by the ratio a/b of the layer widths of metamaterial photonic superlattices, for both transverse electric and transverse magnetic polarizations, in order to have an omnidirectional (n) = 0 gap. The present study indicates new perspectives in the design and development of future optical devices.

Pressure, temperature, and thickness dependence of transmittance in a 1D superconductor-semiconductor photonic crystal

Using the transfer matrix method, we study the transmittance of 1D photonic crystals made of alternated layers of a semiconductor (GaAs) and a high-Tc superconductor (HgBa2Ca2Cu3O8+δ) under the effects of temperature, applied hydrostatic pressure, and thickness of the layers. The frequency-dependent dispersion formula according to the two-fluid model was adopted to describe the optical response of the superconducting system. We found that increasing the superconductor (semiconductor) layer thickness results in a shift to higher (lower) values of the transmittance cutoff frequency. Additionally, this cutoff frequency is shifted to lower values with the temperature increase. Furthermore, we found that the width of the photonic bandgaps varies with the applied pressure. The most notorious variation is presented near the 17u2009THz region, where a new gap appears with the increase in pressure. We hope this work may be taken into consideration for the development of new perspectives in the design of new optical de...

Laser-dressing and magnetic-field effects on shallow-donor impurity states in semiconductor GaAs–Ga1−xAlxAs cylindrical quantum-well wires

The influence of an intense laser field on shallow-donor states in cylindrical GaAs-Ga(1-x)Al(x)As quantum-well wires under an external magnetic field applied along the wire axis is theoretically studied. Numerical calculations are performed in the framework of the effective-mass approximation, and the impurity energies corresponding to the ground state and 2p(±) excited states are obtained via a variational procedure. The laser-field effects on the shallow-donor states are considered within the extended dressed-atom approach, which allows one to treat the problem impurity + heterostructure + laser field + magnetic field as a renormalized impurity + heterostructure + magnetic field problem, in which the laser effects are taken into account through a renormalization of both the conduction-band effective mass and fundamental semiconductor gap.

Band structure of a 2D photonic crystal based on ferrofluids of Co0.8Zn0.2Fe2O4 nanoparticles under perpendicular applied magnetic fields

Using a ferrofluid of cobalt-zinc ferrite nanoparticles (Co0.8Zn0.2Fe2O4) coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps.

Magnetic field role on the structure and optical response of photonic crystals based on ferrofluids containing Co0.25Zn0.75Fe2O4 nanoparticles

Ferrofluids based on magnetic Co0.25Zn0.75Fe2O4 ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO4, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co0.25Zn0.75Fe2O4 samples showed superparamagnetic behavior, according to hysteresis loop results. Taking in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferr...

Landég-factor and cyclotron effective mass in a cylindrical GaAs-(Ga,Al)As quantum pillbox under the influence of an axis-parallel applied magnetic field

We have performed a theoretical study of electronic states and the parallel Landeg-factor in a quantum dot (QD), assumed to be in the form of a pillbox, in the presence of an uniform magnetic field applied parallel to the pillbox axis. The quantum pillbox is assumed to consist of a finite length cylinder of GaAs material surrounded by Ga1-xAlxAs which describe the realistic finite potential confinement. The calculations have been performed by using the Kummer confluent hypergeometric functions. This study is performed for different radii and lengths of the cylindrical GaAs pillbox and the limit cases have been studied to prove the validity of the model. Our results are in good agreement with the previous theoretical results [F.E. Lopez, B.A. Rodriguez, E. Reyes-Gomez, L.E. Oliveira, in press] in the limit geometry of a quantum well wire (QWW).

Effects of geometry, applied hydrostatic pressure and magnetic field on the electron-hole transition energy in a GaAs-Ga 1-x Al x As pillbox immersed in a system of Ga 1-y Al y As

In this work, we study the behavior of the electron-hole transition energy in a GaAs-Ga1-xAlxAs pillbox immersed in a system of Ga1-yAlyAs as a function of thickness of the ladder barrier potential for a fixed length of the pillbox, length of the pillbox, thickness of the ladder barriers and pillbox position in the host of Ga1-yAlyAs. The behavior of the electron-hole transition energy as a function of an applied hydrostatic pressure and an applied magnetic field is also studied. For both electron and hole we found that in the strong confinement regime (L≤10A) energy of the ground state as function of the position of the pillbox relative to the ladder barrier potential presents a behavior similar to the binding energy of a hydrogenic impurity in quantum wells, quantum wires and quantum dots [L. Esaki, R. Tsu, IBM J. Res. Dev. 14 (1970) 61; G. Bastard, Phys. Rev. B 24 (1981) 4714; N. Porras-Montenegro, J. Lopez-Gondar, L.E. Oliveira, Phys. Rev. B 43 (1991) 1824]. Electron-heavy hole transition energies increase with the applied magnetic field. Also, we have found that these transition energies, as a function of the applied hydrostatic pressure, present an excellent agreement with experimental reports by Venkateswaran et al. [phys. Rev. B 33 (1986) 8416].

Coupling-barrier and non-parabolicity effects on the conduction electron cyclotron effective mass and Landé factor in GaAs double quantum wells

We have performed a theoretical study of the effects of the non-parabolicity and coupling barrier in between GaAs quantum wells on the conduction electron cyclotron effective mass and Landé [Formula: see text] factor under the action of a growth-direction applied magnetic field. Numerical calculations are performed within the effective mass approximation and taking into account the non-parabolicity effects for the conduction-band electrons, by means of the Ogg-McCombe effective Hamiltonian. The system consists of two GaAs quantum wells connected by a Ga(1 - x)Al(x)As barrier and surrounded by Ga(1 - y)Al(y)As material. We have found that both the [Formula: see text] factor and the cyclotron effective mass are sensitive to the coupling strength, that is the height and width of the barrier in between the GaAs quantum wells. This behavior is similar for every Landé [Formula: see text] factor and the cyclotron effective mass calculated for different Landau levels. It is noticeable that the splitting between the [Formula: see text] and [Formula: see text] cyclotron effective mass increases with the central barrier width and the growth-direction applied magnetic field. As in a single quantum well, we found that the electron Landé [Formula: see text] factor increases with the growth-direction applied magnetic field, comparing quite well with the experimental reports, and that the magnetic field plays an important role in decoupling the quantum wells of the system. Additionally, we have studied the electron cyclotron effective mass and Landé g factor as functions of the Landau levels, depending on the non-parabolicity. From this result one can infer that their population must be taken into account for a complete study of the band parameters as has been proposed in previous works. The present theoretical results are in very good agreement with previous experimental reports in the limiting geometry of a single quantum well.

The electron Landé g factor in GaAs‐(Ga, Al)As coupled quantum wells

Nowadays there is a lot of work devoted to the study of the electron Lande g factor in semiconducting low dimensional structures due to its potential technological applications. Therefore manipulation of the electron Lande g factor by means of the control of the electron confinement, applied magnetic field and applied hydrostatic pressure offers the possibility of having a wide range of ways to control single qubit operation and to have pure spin states to guarantee that no losses occur when the electron spin transports information. This may be achieved by manipulating the electron Lande g factor in semiconductor heterostructures designing appropriate external gate control devices. In this work we study the electron Lande g factor in GaAs‐(Ga, Al) coupled quantum wells in the presence of growth direction applied magnetic field, using the Ogg‐McCombe effective Hamiltonian for the electron in the conduction band in GaAs‐(Ga, Al) coupled quantum wells, which includes nonparabolicity and anisotropy effects. O...