arXiv subjects

F. Ramirez

Publications and source records attributed to F. Ramirez.

4 recordsLinked to original sources

arXiv2019

Systematical study of optical potential strengths in reactions involving strongly, weakly bound and exotic nuclei on $^{120}$Sn

We present new experimental angular distributions for the elastic scattering of $^6$Li$+^{120}$Sn at three bombarding energies. We include these data in a wide systematic involving the elastic scattering of $^{4,6}$He, $^7$Li, $^9$Be, $^{10}$B and $^{16,18}$O projectiles on the same target at energies around the respective Coulomb barriers. Considering this data set, we report on optical model analyses based on the double-folding Sao Paulo Potential. Within this approach, we study the sensitivity of the data fit to different models for the nuclear matter densities and to variations in the optical potential strengths.

nucl-th↗

arXiv2015

High-precision laser spectroscopy of the CO A$^1Π$ - X$^1Σ^+$ (2,0), (3,0) and (4,0) bands

High-precision two-photon Doppler-free frequency measurements have been performed on the CO A$^1Π$ - X$^1Σ^+$ fourth-positive system (2,0), (3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for rotational quantum numbers up to $J = 5$, have been determined at an accuracy of $1.6\times10^{-3}$ cm$^{-1}$, using advanced techniques of two-color 2+1' resonance-enhanced multi-photon ionization, Sagnac interferometry, frequency-chirp analysis on the laser pulses, and correction for AC-Stark shifts. The accurate transition frequencies of the CO A$^1Π$ - X$^1Σ^+$ system are of relevance for comparison with astronomical data in the search for possible drifts of fundamental constants in the early universe. The present accuracies in laboratory wavelengths of $Δλ/λ= 2 \times 10^{-8}$ may be considered exact for the purpose of such comparisons.

physics.atom-ph↗

arXiv1998

Correlation and symmetry effects in transport through an artificial molecule

Spectral weights and current-voltage characteristics of an artificial diatomic molecule are calculated, considering cases where the dots connected in series are in general different. The spectral weights allow us to understand the effects of correlations, their connection with selection rules for transport, and the role of excited states in the experimental conductance spectra of these coupled double dot systems (DDS). An extended Hubbard Hamiltonian with varying interdot tunneling strength is used as a model, incorporating quantum confinement in the DDS, interdot tunneling as well as intra- and interdot Coulomb interactions. We find that interdot tunneling values determine to a great extent the resulting eigenstates and corresponding spectral weights. Details of the state correlations strongly suppress most of the possible conduction channels, giving rise to effective selection rules for conductance through the molecule. Most states are found to make insignificant contributions to the total current for finite biases. We find also that the symmetry of the structure is reflected in the I-V characteristics, and is in qualitative agreement with experiment.

cond-mat.mes-hall↗

arXiv1996

Coulomb effects in artificial molecules

We study the capacitance spectra of artificial molecules consisting of two and three coupled quantum dots from an extended Hubbard Hamiltonian model that takes into account quantum confinement, intra- and inter-dot Coulomb interaction and tunneling coupling between all single particle states in nearest neighbor dots. We find that, for weak coupling, the interdot Coulomb interaction dominates the formation of a collective molecular state. We also calculate the effects of correlations on the tunneling probability through the evaluation of the spectral weights, and corroborate the importance of selection rules for understanding experimental conductance spectra.

cond-mat↗