Browsing by Author "Sierra-Ortega, Jose"

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Double Quantum Ring under an Intense Nonresonant Laser Field: Zeeman and Spin-Orbit Interaction Effects
(MDPI, 2023) Mora-Ramos, Miguel E.; Vinasco, Juan A.; Radu, Adrian; Restrepo, Ricardo L.; Morales, Alvaro L.; Sahin, Mehmet; Mommadi, Omar; Sierra-Ortega, Jose; Escorcia-Salas, Gene Elizabeth; Heyn, Christian; Duque, Derfrey A.; Duque, Carlos A.; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
We theoretically investigate the properties of an electron energy spectrum in a double GaAs-Al0.3Ga0.7As quantum ring by using the effective mass and adiabatic approximations, together with a realistic description of the confining potential profile, which is assumed to be deformed due to the application of an intense nonresonant laser field. The effects of the applied magnetic field and spin-orbit interaction are included. We discuss the features of the lowest confined energy levels under a variation of magnetic field strengths and intense laser parameters. The influence of this external probe on the linear optical absorption response associated with interlevel transitions is analyzed by considering both the presence and absence of spin-orbit effects.
Elliptical Quantum Rings with Variable Heights and under Spin-Orbit Interactions
(MDPI, 2023) Mora-Ramos, Miguel E.; Vinasco, Juan A; Radu, A.; Restrepo, Ricardo L.; Morales, Alvaro L.; Sahin, Mehmet; Mommadi, Omar; Sierra-Ortega, Jose; Escorcia-Salas, Gene Elizabeth; Duque, Carlos A.; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
We investigate the electronic properties of a semiconductor quantum ring with an elliptical shape and non-uniform height, allowing for distributed quantum-dot-like bulges along its perimeter. The adiabatic approximation and the finite element method are combined to calculate the allowed electron states in the structure under the effective mass approximation, considering the contributions from Rashba and Dresselahaus spin–orbit interactions and the Zeeman effect in the presence of an applied magnetic field. We discuss the features of the calculated spectra for two different ring geometries: a symmetric one with four dot-like bulges, and an asymmetric one with three hilled protuberances. The information about those states allows us to evaluate the linear optical absorption response associated with interlevel transitions between the ground and lowest excited states. This phenomenon takes place at resonant energies of only a few milielectronvolts. It is observed that spin–orbit interactions tend to quench this response under zero-field conditions in the case of symmetric confinement.
Optical Properties in a ZnS/CdS/ZnS Core/Shell/Shell Spherical Quantum Dot: Electric and Magnetic Field and Donor Impurity Effects
(MDPI, 2023) Sahin, Mehmet; Toscano-Negrette, Rafael G.; Leon-Gonzalez, Jose C.; Vinasco, Juan A.; Morales, A. L.; Koc, Fatih; Kavruk, Ahmet Emre; Mora-Ramos, M. E; Sierra-Ortega, Jose; Martinez-Orozco, J. C.; Restrepo, R. L; Duque, C. A.; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrödinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations of internal dot radius, the application of electric and magnetic fields (both oriented along z-direction), as well as the presence of on-center donor impurity. Reported optical properties are the absorption and relative refractive index change coefficients. These quantities are related to transitions between the ground and first excited states, with linearly polarized incident radiation along the z-axis. It is found that transition energy decreases with the growth of internal radius, thus causing the red-shift of resonant peaks. The same happens when the external magnetic field increases. When the strength of applied electric field is increased, the opposite effect is observed, since there is a blue-shift of resonances. However, dipole matrix moments decrease drastically with the increase of the electric field, leading to a reduction in amplitude of optical responses. At the moment impurity effects are activated, a decrease in the value of the energies is noted, significantly affecting the ground state, which is more evident for small internal radius. This is reflected in an increase in transition energies.