arXiv subjects

Luiz N. Oliveira

Publications and source records attributed to Luiz N. Oliveira.

9 recordsLinked to original sources

arXiv2026

Real-space renormalization-group study of decoherence and revival following a sudden quench in a finite system

To investigate the nonequilibrium dynamics of a quantum impurity system, we examine two physical properties for the spinless resonant level model subject to sudden quenches of the hybridization between the impurity and the metal. We compute the time dependence of the impurity occupation and survival probability (fidelity) as probes of the dephasing induced by particle-hole excitations. For finite systems, the loss of coherence is only apparent, as discrete spectra lead to quasi-periodic dynamics and revivals when phases realign. We show that a hybrid linear-logarithmic discretization suppresses these finite-size artifacts by rendering the excitation energies incommensurate, thereby reducing revivals. Starting from the Rabi oscillations in the single-site limit of the tight-binding model describing the metal, we extend the analysis to large lattices, where damping and relaxation emerge. Our combination of analytical and numerical results offers a unified picture of the crossover from coherent oscillations to effectively irreversible decoherence.

cond-mat.mes-hall↗

arXiv2021

Real-space numerical renormalization-group computation of transport properties in the side-coupled geometry

The equilibrium transport properties of an elementary nanostructured device with side-coupled geometry are computed and related to universal functions. The computation relies on a real-space formulation of the numerical renormalization-group (NRG) procedure. The real-space construction, dubbed eNRG, is more straightforward than the NRG discretization and allows more faithful description of the coupling between quantum dots and conduction states. The procedure is applied to an Anderson-model description of a quantum wire side-coupled to a single quantum dot. A gate potential controls the dot occupation. In the Kondo regime, the electrical conductance through this device is known to map linearly onto a universal function of the temperature scaled by the Kondo temperature. Here, the energy moments from which the Seebeck coefficient and the thermal conductance can be computed are shown to map linearly onto universal functions also. The moments and transport properties computed by the eNRG procedure are shown to agree very well with these analytical developments. Algorithms facilitating comparison with experimental results are discussed. As an illustration, one of the algorithms is applied to thermal dependence of the thermopower measured by Köhler [PhD Thesis, TUD, Dresden, 2007] in Lu$_{0.9}$Yb$_{0.1}$Rh$_{2}$Si$_{2}$.

cond-mat.str-el↗

arXiv2019

Approximate expression for the ground-state energy of the two- and three-dimensional Hubbard model at arbitrary filling obtained from dimensional scaling

We generalize the linear discrete dimensional scaling approach for the repulsive Hubbard model to obtain a nonlinear scaling relation that yields accurate approximations to the ground-state energy in both two and three dimensions, as judged by comparison to auxiliary-field quantum Monte Carlo (QMC) data. Predictions are made for the per-site ground-state energies in two and three dimensions for $n$ (filling factor) and $U$ (Coulomb interaction) values for which QMC data are currently unavailable.

cond-mat.str-el↗

arXiv2018

Monty Hall problem revisited once more

The Monty Hal problem is an attractive puzzle. It combines simple statement with answers that seem surprising to most audiences. The problem was thoroughly solved over two decades ago. Yet, more recent discussions indicate that the solution is incompletely understood. Here, we review the solution and discuss pitfalls and other aspects that make the problem interesting.

math.HO↗

arXiv2018

Entanglement in finite quantum systems under twisted boundary conditions

In a recent publication, we have discussed the effects of boundary conditions in finite quantum systems and their connection with symmetries. Focusing on the one-dimensional Hubbard Hamiltonian under twisted boundary conditions, we have shown that properties, such as the ground-state and gap energies, converge faster to the thermodynamical limit ($L \rightarrow \infty$) if a special torsion $Θ^*$ is adjusted to ensure particle-hole symmetry. Complementary to the previous research, the present paper extends our analysis to a key quantity for understanding correlations in many-body systems: the entanglement. Specifically, we investigate the average single-site entanglement $\langle S_j \rangle$ as a function of the coupling $U/t$ in Hubbard chains with up to $L=8$ sites and further examine the dependence of the per-site ground-state $ε_0$ on the torsion $Θ$ in different coupling regimes. We discuss the scaling of $ε_0$ and $\langle S_j \rangle$ under $Θ^*$ and analyse their convergence to Bethe Ansatz solution of the infinite Hubbard Hamiltonian. Additionally, we describe the exact diagonalization procedure used in our numerical calculations and show analytical calculations for the case-study of a trimer.

cond-mat.str-el↗

arXiv2018

How sharply does the Anderson model depict a single-electron transistor?

The single-impurity Anderson model has been the focus of theoretical studies of molecular junctions and the single-electron transistor, a nanostructured device comprising a quantum dot that bridges two otherwise decoupled metallic leads. The low-temperature transport properties of the model are controlled by the ground-state occupation of the quantum dot, a circumstance that recent density-functional approaches have explored. Here we show that the ground-state dot occupation also parametrizes a linear mapping between the thermal dependence of the zero-bias conductance and a universal function of the temperature scaled by the Kondo temperature. Careful measurements by Grobis and co-workers are very accurately fitted by the universal mapping. Nonetheless, the dot occupation and an asymmetry parameter extracted from the same mapping are relatively distant from the expected values. We conclude that mathematical results derived from the model Hamiltonian reproduce accurately the universal physical properties of the device. In contrast, non-universal features cannot be reproduced quantitatively. To circumvent this limitation, \emph{ab initio} studies of the device at high energies seem necessary, to accurately define the model Hamiltonian. Our conclusion reinforces findings by Gross and coworkers, who applied time-dependent density-functional theory to show that, to describe the low-energy properties of molecular junctions, one must be able to describe the high-energy regime.

cond-mat.str-el↗

arXiv2015

Kondo dynamics in one-dimensional doped ferromagnetic insulators

Some well-established examples of itinerant-electron ferromagnetism in one dimension occur in a Mott-insulating phase. We examine the consequences of doping a ferromagnetic insulator and cou- pling magnons to gapless charge fluctuations. Using a bosonization scheme for strongly interacting electrons, we derive an effective field theory for the magnon-holon interaction. When the magnon momentum matches the Fermi momentum of the holons, the backscattering of the magnon at low energies gives rise to a Kondo effect of a pseudospin defined from the chirality degree of freedom (right- or left-moving particles). The crossover between weak-coupling and strong-coupling fixed points of the effective mobile-impurity model is then investigated using a numerical renormalization group approach.

cond-mat.str-el↗

arXiv2009

Universality and the zero-bias conductance of the single-electron transistor

The thermal dependence of the electrical conductance of the single-electron transistor (SET) in the zero-bias Kondo regime is discussed. An exact mapping to the universal curve for the symmetric Anderson model is established. Linear, the mapping is parametrized by the Kondo temperature and the charge in the Kondo cloud. Illustrative numerical renormalization-group results, in excellent agreement with the mapping, are presented.

cond-mat.mes-hall↗

arXiv2008

Density-functional description of superconducting and magnetic proximity effects across a tunneling barrier

A density-functional formalism for superconductivity {\em and} magnetism is presented. The resulting relations unify previously derived Kohn-Sham equations for superconductors and for non-collinear magnetism. The formalism, which discriminates Cooper pair singlets from triplets, is applied to two quantum liquids coupled by tunneling through a barrier. An exact expression is derived, relating the eigenstates and eigenvalues of the Kohn-Sham equations, unperturbed by tunneling, on one side of the barrier to the proximity-induced ordering potential on the other.

cond-mat.mtrl-sci↗