L. Costa Ribeiro

Federal Center for Technological Education Celso Suckow da Fonseca

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E. V. Anda

Pontifical Catholic University of Rio de Janeiro

G. B. Martins

Universidade Federal de Uberlândia

I. J. Hamad

Institute of Physics Rosario

G. Chiappe

University of Alicante

R. S. Dutra

Rio de Janeiro Federal Institute of Education, Science and Technology

E. Vernek

Universidade Federal de Uberlândia

C.M. Porto

Universidade Federal Rural do Rio de Janeiro

Victor Lopes

University of Alicante

Elbio Dagotto

University of Tennessee at Knoxville

E. Louis

University of Alicante

Cooperative Institutions

Pontifical Catholic University of Rio de Janeiro

University of Alicante

Oak Ridge National Laboratory

Florida State University

National High Magnetic Field Laboratory

University of Tennessee at Knoxville

Federal Center for Technological Education Celso Suckow da Fonseca

University of New Mexico

University of California, Santa Barbara

Scuola Internazionale Superiore di Studi Avanzati

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The spatial range of the Kondo effect: a numerical analysis

arXiv (Cornell University) (2009)

C. A. Büsser G. B. Martins L. Costa Ribeiro E. Vernek E. V. Anda

The spatial length of the Kondo screening is still a controversial issue related to Kondo physics. While renormalization group and Bethe Anzats solutions have provided detailed information about the thermodynamics of magnetic impurities, they are insufficient to study the effect on the surrounding electrons, i.e., the spatial range of the correlations created by the Kondo effect between the localized magnetic moment and the conduction electrons. The objective of this work is to present a quantitative way of measuring the extension of these correlations by studying their effect directly on the local density of states (LDOS) at arbitrary distances from the impurity. The numerical techniques used, the Embedded Cluster Approximation, the Finite U Slave Bosons, and Numerical Renormalization Group, calculate the Green functions in real space. With this information, one can calculate how the local density of states away from the impurity is modified by its presence, below and above the Kondo temperature, and then estimate the range of the disturbances in the non-interacting Fermi sea due to the Kondo effect, and how it changes with the Kondo temperature $T_{\rm K}$. The results obtained agree with results obtained through spin-spin correlations, showing that the LDOS captures the phenomenology of the Kondo cloud as well. To the best of our knowledge, it is the first time that the LDOS is used to estimate the extension of the Kondo cloud.

10.48550/arxiv.0906.2951

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Transport properties of a two-impurity system: A theoretical approach

Physical Review B (2013)

I. J. Hamad L. Costa Ribeiro G. B. Martins E. V. Anda

A system of two interacting cobalt atoms, at varying distances, was studied in a recent scanning tunneling microscope experiment by Bork et. al.[Nature Phys. 7, 901 (2011)]. We propose a microscopic model that explains, for all experimentally analyzed interatomic distances, the physics observed in these experiments. Our proposal is based on the two-impurity Anderson model, with the inclusion of a two-path geometry for charge transport. This many-body system is treated in the finite-U slave boson mean-field approximation and the logarithmic-discretization embedded-cluster approximation. We physically characterize the different charge transport regimes of this system at various interatomic distances and show that, as in the experiments, the features observed in the transport properties depend on the presence of two impurities but also on the existence of two conducting channels for electron transport. We interpret the splitting observed in the conductance as the result of the hybridization of the two Kondo resonances associated with each impurity.

Anderson impurity model

10.1103/physrevb.87.115102

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Uma aplicação da dinâmica de uma partícula em uma trajetória predeterminada: o problema do iglu elipsoidal

Revista Brasileira de Ensino de Física (2018)

R. S. Dutra L. Costa Ribeiro C.M. Porto

Resumo Neste trabalho o problema clássico de uma partícula que descreve um arco de círculo ao deslizar pela superfície polida de um iglu esférico é estendido para o caso de um iglu elipsoidal. Neste caso, a altura na qual a partícula perde contato com a superfície do iglu passa a obedecer a uma equação cúbica com coeficientes que dependem dos parâmetros que determinam a trajetória elíptica. A solução analítica dessa equação é então obtida a partir do método de Cardano-Tartaglia.

10.1590/1806-9126-rbef-2018-0185

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Transport across two interacting quantum dots: Bulk Kondo, Kondo box, and molecular regimes

Physical Review B (2014)

L. Costa Ribeiro I. J. Hamad G. Chiappe E. V. Anda

We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. We finally study how the transport properties are affected as N is increased. For the study we used exact multiconfigurational Lanczos calculations and finite-$U$ slave-boson mean-field theory at $T=0$. The results obtained with both methods describe qualitatively and also quantitatively the same physics.

Kondo insulator

Slave boson

10.1103/physrevb.89.045412

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Maximizing tangential frictional forces effects in bidimensional collisions: a study of the tangent restitution coefficient through a video analysis approach

Revista Brasileira de Ensino de Física (2023)

Anderson Rocha R. S. Dutra L. Costa Ribeiro

In this work we used the video analysis technique to investigate the contribution of the friction forces to the dynamic of a series of oblique collisions of a basketball against the floor’s surface. This contribution was evaluated through the tangent restitution coefficients associated to these collisions, which, in general, presented values distinct from the unit, proving, thus, its importance. Additionally, the appreciably values bigger than unity obtained for this quantity quantitatively confirms the physical scenario suggested in a previous work by some of the authors [1] which is governed by the torques transmitted to the ball during the successive collisions and characterized by variations on the magnitudes and even on the directions of the friction forces. To support this dynamic we considered a ball of relatively sizeable radius and mass, and launched with a certain spin velocity. Also, in order to increase the friction coefficient, the floor’s surface was covered with a rough and rubberized material.

Coefficient of restitution

Ball (mathematics)

Normal force

Coefficient of friction

Dynamical friction

Contact force

10.1590/1806-9126-rbef-2022-0277

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Three stage Kondo effect in a three quantum dot system

APS March Meeting Abstracts (2014)

G. Chiappe L. Costa Ribeiro I. J. Hamad E. V. Anda

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Influence of spin correlations in the transport properties of a double quantum dot system

Bulletin of the American Physical Society (2013)

I. J. Hamad L. Costa Ribeiro G. Chiappe E. V. Anda

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Totally Spin-Polarized Currents in an Interferometer with Spin–Orbit Coupling and the Absence of Magnetic Field Effects

Nanomaterials (2022)

Victor Lopes G. Chiappe L. Costa Ribeiro E. V. Anda

The paper studies the electronic current in a one-dimensional lead under the effect of spin-orbit coupling and its injection into a metallic conductor through two contacts, forming a closed loop. When an external potential is applied, the time reversal symmetry is broken and the wave vector k of the circulating electrons that contribute to the current is spin-dependent. As the wave function phase depends upon the vector k, the closed path in the circuit produces spin-dependent current interference. This creates a physical scenario in which a spin-polarized current emerges, even in the absence of external magnetic fields or magnetic materials. It is possible to find points in the system's parameter space and, depending upon its geometry, the value of the Fermi energy and the spin-orbit intensities, for which the electronic states participating in the current have only one spin, creating a high and totally spin-polarized conductance. For a potential of a few tens of meV, it is possible to obtain a spin-polarized current of the order of μA. The properties of the obtained electronic current qualify the proposed device as a potentially important tool for spintronics applications.

Spin–orbit interaction

10.3390/nano12224082

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E se a superfície for áspera? Um estudo sobre a influência da força de atrito em colisões inelásticas através de videoanálise

Revista Brasileira de Ensino de Física (2021)

Reyva Franco V.S. Miranda R. S. Dutra L. Costa Ribeiro

Este trabalho apresenta um estudo que explica a física associada ao conjunto das sucessivas colisões inelásticas de um sólido esférico contra a superfície rígida do piso do laboratório, após ser lançado de uma determinada altura. O centro de massa do sólido é rastreado a partir da videoanálise realizada através do conhecido software educacional Tracker, possibilitando a obtenção da velocidade de seu centro de massa durante todo o caminho percorrido. O momento linear do sólido é obtido nos instantes imediatamente antes e após as colisões, permitindo o cálculo de sua dissipação, assim como da dissipação da energia cinética, durante esses eventos. O papel desempenhado pela força de atrito durante as colisões também é avaliado, através de uma grandeza pouco conhecida na literatura de física básica, designada por coeficiente de restituição tangencial. Medidas dessa grandeza apresentaram valores próximos à unidade e, portanto, revelaram quantitativamente que, para o experimento realizado, é ínfima a contribuição da força de atrito para o impulso durante as colisões, se comparada à fornecida pela força normal, também exercida pelo piso do laboratório. Esse resultado é implicitamente considerado em modelos de colisões apresentados em livros didáticos de física básica, onde, sem nenhuma justificativa, a força de atrito é ignorada.

10.1590/1806-9126-rbef-2020-0528

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Citations (1)

Numerical analysis of the spatial range of the Kondo effect

Physical Review B (2010)

C. A. Büsser G. B. Martins L. Costa Ribeiro E. Vernek E. V. Anda

The spatial length of the Kondo screening is still a controversial issue related to Kondo physics. While renormalization-group and Bethe-Ansatz solutions have provided detailed information about the thermodynamics of magnetic impurities, they are insufficient to study the effect on the surrounding electrons, i.e., the spatial range of the correlations created by the Kondo effect between the localized magnetic moment and the conduction electrons. The objective of this work is to present a quantitative way of measuring the extension of these correlations by studying their effect directly on the local density of states (LDOS) at arbitrary distances from the impurity. The numerical techniques used, the embedded cluster approximation, the finite-$U$ slave bosons, and numerical renormalization group, calculate the Green's functions in real space. With this information, one can calculate how the local density of states away from the impurity is modified by its presence, below and above the Kondo temperature, and then estimate the range of the disturbances in the noninteracting Fermi sea due to the Kondo effect, and how it changes with the Kondo temperature ${T}_{\text{K}}$. The results obtained agree with results obtained through spin-spin correlations, showing that the LDOS captures the phenomenology of the Kondo cloud as well.

Anderson impurity model

Kondo insulator

Bethe ansatz

Ansatz

Magnetic impurity

10.1103/physrevb.81.045111

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Citations (51)