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Papers by Adriano Martins

Research paper thumbnail of Mechanisms of interlayer exciton emission and giant valley polarization in van der Waals heterostructures

Research paper thumbnail of Simulated annealing method for molecular constants calculation: the electronic transition A2Σ+–X2Π of N2O+ radical 000–000 and 001–001 band cases

Molecular Physics, 2021

The Simulated Annealing (SA) method is here first adopted to retrieve the molecular constants use... more The Simulated Annealing (SA) method is here first adopted to retrieve the molecular constants used to fit wavenumbers into a model, from a vibrational band of the electronic transition A of the N O radical, 000–000, starting from a set of molecular constants obtained in a previous work, and varying their values within a range in order to mimic an error in each one parameter used. The SA calculations have been carried out following the proposal of Vanderbilt and Louie for performing a minimisation of an objective function where the parameters are continuous variables whose values can vary. Through SA, the 280 experimentally wavenumbers from the previous work were reduced using a Hamiltonian model and new molecular constants obtained. A comparison among the results obtained through a nonlinear deterministic model and the retrieved values obtained using the SA shows that the simulated annealing can be considered as a very strong method for molecular constants determination. Second, intending to test the SA method in a direct fit to obtain the molecular constants, the 142 wavenumbers from the 001–001 band A electronic transition of the N O were studied in this work and the molecular constants analysed. GRAPHICAL ABSTRACT

Research paper thumbnail of Note: Cold spectra of the electronic transition A2Σ+-X2Π of N2O+ radical: High resolution analysis of the bands 000-100, 100-100, and 001-101

The Journal of Chemical Physics, 2015

In this note, three vibrational bands of the electronic transition A2Σ+-X2Π of the N2O+ radical (... more In this note, three vibrational bands of the electronic transition A2Σ+-X2Π of the N2O+ radical (000-100, 100-100, and 001-101) were theoretically analysed. Starting from Hamiltonian models proposed for this kind of molecule, their parameters were calculated using a Levenberg-Marquardt fit procedure in order to reduce the root mean square deviation from the experimental transitions below to 0.01 cm−1. The main objective of this work is to obtain new and reliable values for rotational constant B″ and the spin-orbit interaction parameter A of the analysed vibrational levels of the X2Π electronic state of this molecule.

Research paper thumbnail of Comment on "Line of Dirac Nodes in Hyperhoneycomb Lattices

Physical review letters, Jun 17, 2016

Research paper thumbnail of An elastic model for the In–In correlations in InxGa1−xAs semiconductor alloys

Solid State Communications, 2000

Research paper thumbnail of The Nature of Shallow-State Wave Functions in Semiconductors

physica status solidi (b), 2002

ABSTRACT The problem of donor impurities is revisited within the tight-binding (TB) framework, yi... more ABSTRACT The problem of donor impurities is revisited within the tight-binding (TB) framework, yielding an atomistic description of the impurity levels and their wave functions. Finite-size scaling is used in order to extrapolate our supercell calculations to the bulk limit. Special attention is given to the analysis of the defect wave function and comparison with the effective mass theory (EMT) predictions.

Research paper thumbnail of Semiconductor Hetrostructures with Non-Ideal Interfaces: Electronic Structure and Optical Properties

physica status solidi (a), 1999

ABSTRACT

Research paper thumbnail of Au and Cu Atoms on NaCl(001): a single-atom based memory device prototype?

The European Physical Journal B, 2010

Research paper thumbnail of Silicon-based spin and charge quantum computation

Anais da Academia Brasileira de Ciências, 2005

Silicon-based quantum-computer architectures have attracted attention because of their promise fo... more Silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus) in Si are ideal candidates for qubits in such proposals due to the relatively long spin coherence times. For these spin qubits, donor electron charge manipulation by external gates is a key ingredient for control and read-out of single-qubit operations, while shallow donor exchange gates are frequently invoked to perform two-qubit operations. More recently, charge qubits based on tunnel coupling in P+2 substitutional molecular ions in Si have also been proposed. We discuss the feasibility of the building blocks involved in shallow donor quantum computation in silicon, taking into account the peculiarities of silicon electronic structure, in particular the six degenerate states at ...

Research paper thumbnail of Revisiting Spin Glasses: Impact of Spin-Spin Interaction Range

Brazilian Journal of Physics, 2017

Research paper thumbnail of Energy of Ni/Ni3Al interface: A temperature-dependent theoretical study

Research paper thumbnail of Optical effects of interdiffusion in GaAs/AlAs heterostructures: Atomic scale calculations

Applied Physics Letters, 1996

We investigate the effects of atomic interdiffusion in the optical properties of AlAs/GaAs quantu... more We investigate the effects of atomic interdiffusion in the optical properties of AlAs/GaAs quantum wells through tight-binding model calculations. Ensembles of supercells, each cell containing up to ∼104 atoms with periodic boundary conditions, are used to simulate the heterostructures. The oscillator strength f of optical transitions at the absorption threshold is calculated as a function of the quantum-wells width W and the diffusion length L. As L increases, f undergoes a discontinuous transition to zero, indicating indirect-gap behavior for L larger than a critical value of the diffusion length. A unified behavior of f as a function of L/W1.7 is found. This permits relating optical properties to structural properties through simple fitting formulas.

Research paper thumbnail of Atomistic description of shallow levels in semiconductors

Research paper thumbnail of Conduction-band tight-binding description for Si applied to P donors

Research paper thumbnail of Anisotropic Electronic Structure and Transport Properties of the H-0 Hyperhoneycomb Lattice

The Journal of Physical Chemistry C, 2017

Research paper thumbnail of Electric-field control and adiabatic evolution of shallow donor impurities in silicon

Research paper thumbnail of Mechanisms of interlayer exciton emission and giant valley polarization in van der Waals heterostructures

Research paper thumbnail of Simulated annealing method for molecular constants calculation: the electronic transition A2Σ+–X2Π of N2O+ radical 000–000 and 001–001 band cases

Molecular Physics, 2021

The Simulated Annealing (SA) method is here first adopted to retrieve the molecular constants use... more The Simulated Annealing (SA) method is here first adopted to retrieve the molecular constants used to fit wavenumbers into a model, from a vibrational band of the electronic transition A of the N O radical, 000–000, starting from a set of molecular constants obtained in a previous work, and varying their values within a range in order to mimic an error in each one parameter used. The SA calculations have been carried out following the proposal of Vanderbilt and Louie for performing a minimisation of an objective function where the parameters are continuous variables whose values can vary. Through SA, the 280 experimentally wavenumbers from the previous work were reduced using a Hamiltonian model and new molecular constants obtained. A comparison among the results obtained through a nonlinear deterministic model and the retrieved values obtained using the SA shows that the simulated annealing can be considered as a very strong method for molecular constants determination. Second, intending to test the SA method in a direct fit to obtain the molecular constants, the 142 wavenumbers from the 001–001 band A electronic transition of the N O were studied in this work and the molecular constants analysed. GRAPHICAL ABSTRACT

Research paper thumbnail of Note: Cold spectra of the electronic transition A2Σ+-X2Π of N2O+ radical: High resolution analysis of the bands 000-100, 100-100, and 001-101

The Journal of Chemical Physics, 2015

In this note, three vibrational bands of the electronic transition A2Σ+-X2Π of the N2O+ radical (... more In this note, three vibrational bands of the electronic transition A2Σ+-X2Π of the N2O+ radical (000-100, 100-100, and 001-101) were theoretically analysed. Starting from Hamiltonian models proposed for this kind of molecule, their parameters were calculated using a Levenberg-Marquardt fit procedure in order to reduce the root mean square deviation from the experimental transitions below to 0.01 cm−1. The main objective of this work is to obtain new and reliable values for rotational constant B″ and the spin-orbit interaction parameter A of the analysed vibrational levels of the X2Π electronic state of this molecule.

Research paper thumbnail of Comment on "Line of Dirac Nodes in Hyperhoneycomb Lattices

Physical review letters, Jun 17, 2016

Research paper thumbnail of An elastic model for the In–In correlations in InxGa1−xAs semiconductor alloys

Solid State Communications, 2000

Research paper thumbnail of The Nature of Shallow-State Wave Functions in Semiconductors

physica status solidi (b), 2002

ABSTRACT The problem of donor impurities is revisited within the tight-binding (TB) framework, yi... more ABSTRACT The problem of donor impurities is revisited within the tight-binding (TB) framework, yielding an atomistic description of the impurity levels and their wave functions. Finite-size scaling is used in order to extrapolate our supercell calculations to the bulk limit. Special attention is given to the analysis of the defect wave function and comparison with the effective mass theory (EMT) predictions.

Research paper thumbnail of Semiconductor Hetrostructures with Non-Ideal Interfaces: Electronic Structure and Optical Properties

physica status solidi (a), 1999

ABSTRACT

Research paper thumbnail of Au and Cu Atoms on NaCl(001): a single-atom based memory device prototype?

The European Physical Journal B, 2010

Research paper thumbnail of Silicon-based spin and charge quantum computation

Anais da Academia Brasileira de Ciências, 2005

Silicon-based quantum-computer architectures have attracted attention because of their promise fo... more Silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus) in Si are ideal candidates for qubits in such proposals due to the relatively long spin coherence times. For these spin qubits, donor electron charge manipulation by external gates is a key ingredient for control and read-out of single-qubit operations, while shallow donor exchange gates are frequently invoked to perform two-qubit operations. More recently, charge qubits based on tunnel coupling in P+2 substitutional molecular ions in Si have also been proposed. We discuss the feasibility of the building blocks involved in shallow donor quantum computation in silicon, taking into account the peculiarities of silicon electronic structure, in particular the six degenerate states at ...

Research paper thumbnail of Revisiting Spin Glasses: Impact of Spin-Spin Interaction Range

Brazilian Journal of Physics, 2017

Research paper thumbnail of Energy of Ni/Ni3Al interface: A temperature-dependent theoretical study

Research paper thumbnail of Optical effects of interdiffusion in GaAs/AlAs heterostructures: Atomic scale calculations

Applied Physics Letters, 1996

We investigate the effects of atomic interdiffusion in the optical properties of AlAs/GaAs quantu... more We investigate the effects of atomic interdiffusion in the optical properties of AlAs/GaAs quantum wells through tight-binding model calculations. Ensembles of supercells, each cell containing up to ∼104 atoms with periodic boundary conditions, are used to simulate the heterostructures. The oscillator strength f of optical transitions at the absorption threshold is calculated as a function of the quantum-wells width W and the diffusion length L. As L increases, f undergoes a discontinuous transition to zero, indicating indirect-gap behavior for L larger than a critical value of the diffusion length. A unified behavior of f as a function of L/W1.7 is found. This permits relating optical properties to structural properties through simple fitting formulas.

Research paper thumbnail of Atomistic description of shallow levels in semiconductors

Research paper thumbnail of Conduction-band tight-binding description for Si applied to P donors

Research paper thumbnail of Anisotropic Electronic Structure and Transport Properties of the H-0 Hyperhoneycomb Lattice

The Journal of Physical Chemistry C, 2017

Research paper thumbnail of Electric-field control and adiabatic evolution of shallow donor impurities in silicon