Marcos Degani - Academia.edu (original) (raw)

Papers by Marcos Degani

Condensed Matter

This modelling work concerns the effects of the interference between two partial subband condensa... more This modelling work concerns the effects of the interference between two partial subband condensates in a quasi-one-dimensional superconducting superlattice. The iterative under-relaxation with phase control method is used to solve Bogoliubov–de Gennes equations in the envelope ansatz. This method—easily generalisable to a wide class of multiband superconducting systems—allows us to obtain both the constructive and the destructive interference solution. The discussion is centred on the latter case, with one of the condensates collapsing with increased inter-subband coupling strength, due to the other—the dominating one—imposing its symmetry on the overall order parameter. The in-depth qualitative analysis is made of underlying intra-subband and inter-subband dynamics, such as the possible factors determining the dominant subband condensate or the ones determining the region where the destructive solution coexists with the constructive one. A comprehensive discussion with the recent ...

Physica E: Low-dimensional Systems and Nanostructures

Superlattices and Microstructures, 2021

IEEE Journal of Quantum Electronics, 2016

In this paper, we show a superlattice quantum well infrared photodetector (S-QWIP) grown by metal... more In this paper, we show a superlattice quantum well infrared photodetector (S-QWIP) grown by metal-organic vapor phase epitaxy with two narrow photocurrent peaks in the mid infrared range due to transitions between the ground state from a quantum well and two excited states localized in the continuum. The structure composed of InGaAs/InAlAs quantum-well lattice matched to InP with a central quantum well acting as an artificial defect. The potential profile is carefully chosen to explore the parity anomaly of the continuum localized states and also to reduce the thermoexcited electrons decreasing the dark current. The photocurrent spectrum shows two peaks with transition energies of 300 and 460 meV (λ/λ of 0.13 and 0.12) at 12 K. The peak detectivity is 1.23×10 10 Jones at 30 K and +5 V. When compared with a regular multiquantum well sample designed to generate photocurrent at the same wavelength, the S-QWIP shows an increase of 15 K on its background-limited performance temperature and a lower dark current for temperatures above 200 K.

Surface Science, 1992

We have investigated the subband energies on Se S-doped GaAs structures by tunneling current. Sel... more We have investigated the subband energies on Se S-doped GaAs structures by tunneling current. Self-consistent calculations including many-body effects were performed to compare the experimental data. It was shown that increasing the gate voltage induces ionization of resonant deep donor. Carrier distribution was determined by capacitance-voltage measurements. The subsequent annealing experiments revealed that significant diffusion of the Se dopant at 700 o C had taken place in ~mparison to the Si dopant case.

Solid State Communications, 1993

A new double channel field-effect structure based on &doping technology is proposed. Resonant tun... more A new double channel field-effect structure based on &doping technology is proposed. Resonant tunneling between the channels is employed to control the transport along the interface plane. A realistic simulation is performed for several temperatures. We solve the Schriidinger and Poisson equations self-consistently and have found that a large peak-tevalley ratio in the current-voltage characteristic occurs at the whole range of temperature investigated. This effect indicates the potential application of this phenomenon for switching devices, where the transversal conductivity can be controlled due to the coupling between states belonging to different channels.

Brazilian Journal of Physics, 1999

We calculate the characteristic current-voltage curve of a tunneling device based on semimagnetic... more We calculate the characteristic current-voltage curve of a tunneling device based on semimagnetic semiconductor materials. The device is a heterostructure with layers of Cd1,xMnxTe in which the magnetic ions Mn 2+ interact strongly with the conducting electrons via the s-d exchange interaction. Thermal uctuations of Mn 2+ magnetic moments cause spin-dependent electron scattering that modi es the characteristic current-voltage curve. Our calculation shows how this electron-ion scattering is expected to a ect the spin dynamics in transport measurements.

Applied Physics Letters, 2014

Photocurrents are calculated for a specially designed GaMnAs semiconductor heterostructure. The r... more Photocurrents are calculated for a specially designed GaMnAs semiconductor heterostructure. The results reveal regions in the infrared range of the energy spectrum in which the proposed structure is remarkably spinselective. For such photon energies, the generated photocurrents are strongly spin-polarized. Application of a relatively small static bias in the growth direction of the structure is predicted to efficiently reverse the spinpolarization for some photon energies. This behavior suggests the possibility of conveniently simple switching mechanisms. The physics underlying the results is studied and understood in terms of the spin-dependent properties emerging from the particular potential profile of the structure.

Brazilian Journal of Physics, 1994

The phonon density-of-states (DOS) of insulating BaBi03 in orthorhombic phase and superconducting... more The phonon density-of-states (DOS) of insulating BaBi03 in orthorhombic phase and superconducting Bal-,K,Bi03 in cubic phase are studied using the molecular dynamics (MD) method. The MD simulations are carried out with an effective interaction potential which includes Coulomb interactions, the charge-dipole interactions due to the electronic polarizability of O--, and steric effects. Partia1 DOS of Ba, K, Bi and O in BaBi03 and Bal-,K,Bi03 are also determined from MD simulations and reveal that phonons above 20 meV are due to oxygen vibrations. The reference oxygen-isotope-effect exponent, a,, = -dln /dln Mo, of Bal-,K,Bi03 is determined to be a,, = 0.42 k 0.05 from the mass (Mo) variation of the first moment of the phonon DOS, l6 and 'v w >. This value is in very good agreement with the oxygen isotope-effect exponent ao, determined experimentally from the variation of Tc, and suggests that Bal-,KxBi03 is a weak-to-moderate coupling BCS-like superconductor and that the high T...

Philosophical Magazine B-Physics of Condensed Matter Statistical Mechanics Electronic Optical and Magnetic Properties, 1993

... This is also in good agreement with the slow diffusion rate of Ge into GaAs as observed by Ka... more ... This is also in good agreement with the slow diffusion rate of Ge into GaAs as observed by Kavanagh and Magee (1987 ... The photoionization energy has little dependence on alloy composition (Mooney 1990) and so this light should be able to excite electrons in the same way ...

Physical Review B

We theoretically investigate electron spin operations driven by applied electric fields in a semi... more We theoretically investigate electron spin operations driven by applied electric fields in a semiconductor double quantum dot (DQD). Our model describes a DQD formed in semiconductor nanowire with longitudinal potential modulated by local gating. The eigenstates for two electron occupation, including spin-orbit interaction, are calculated and then used to construct a model for the charge transport cycle in the DQD taking into account the spatial dependence and spin mixing of states. The dynamics of the system is simulated aiming at implementing protocols for qubit operations, that is, controlled transitions between the singlet and triplet states. In order to obtain fast spin manipulation, the dynamics is carried out taking advantage of the anticrossings of energy levels introduced by the spin-orbit and interdot couplings. The theory of optimal quantum control is invoked to find the specific electric-field driving that performs qubit logical operations. We demonstrate that it is possible to perform within high efficiency a universal set of quantum gates {CNOT, H⊗I, I⊗H, T⊗I, and T⊗I}, where H is the Hadamard gate, T is the π/8 gate, and I is the identity, even in the presence of a fast charge transport cycle and charge noise effects.

Journal of Physics C: Solid State Physics

ABSTRACT The motion of an individual many-electron dimple parallel to the interface of phase-sepa... more ABSTRACT The motion of an individual many-electron dimple parallel to the interface of phase-separated 3He-4He mixtures is described by a Frohlich-type Hamiltonian as for the polaron problem. The authors have applied a simple unitary transformation formalism to evaluate the ground-state energy, effective mass and the radius of such a dimple as a function of the external pressing electric field. The results are compared to those recently obtained by V.B. Shikin and P. Leiderer (1980) within a different context.

MRS Proceedings

ABSTRACTThe phonon densities-of-states (DOS) of superconducting Ba1−xKxBi16O3 and Ba1−xKxBi18O3 (... more ABSTRACTThe phonon densities-of-states (DOS) of superconducting Ba1−xKxBi16O3 and Ba1−xKxBi18O3 (x=0.4) are determined using molecular dynamics (MD) simulations and inelastic neutron scattering measurements. The reference isotope-effect exponent is obtained from the mass variation of the first frequency moment of the phonon DOS. The energy gap, oxygen isotope-effect exponent and electron tunneling characteristics are calculated within the framework of Eliashberg theory of electron-phonon coupling.

AIP Conference Proceedings, 2005

ABSTRACT The purpose of this work is to present a theoretical study on Stark effect and permanent... more ABSTRACT The purpose of this work is to present a theoretical study on Stark effect and permanent dipole moment of vertically confined excitons in ring-like quantum dots of InAs embedded in GaAs. Similarly to what is observed in dots, this system presents blue shift energy when an electric field is applied from the base to the top of the disk.

AIP Conference Proceedings, 2007

ABSTRACT The energy spectrum in semiconductor quantum rings (QR’s) is calculated considering an e... more ABSTRACT The energy spectrum in semiconductor quantum rings (QR’s) is calculated considering an external magnetic field applied perpendicular to those structures. The existence of positive hydrogenic impurities is also investigated, showing that, depending on their signal and localization, they can destroy AB oscillations. The effects on the energy spectrum due to an arbitrary deformation in the QR are considered and we observed that, in some cases the AB oscillations can also be suppressed.

Semiconductor Science and Technology, Nov 7, 2001

ABSTRACT We calculated the effects of a transverse magnetic field on electron-hole exchange inter... more ABSTRACT We calculated the effects of a transverse magnetic field on electron-hole exchange interaction for free excitons in semiconductor quantum wells (QWs). The magnetic field is the source of an anisotropy on the exciton dispersion for motion on the QW plane in directions parallel and perpendicular to the field. Weakening of the exciton binding energy and the exchange interaction terms were predicted for the moving excitons. These effects are better resolved in wide QWs.