In the present work, we investigate the electronic transport through a T-shape double quantum dot... more In the present work, we investigate the electronic transport through a T-shape double quantum dot system coupled to two normal leads and to one superconducting lead. We explore the interplay between Kondo and Andreev states due to proximity effects. We find that Kondo resonance is modified by the Andreev bound states, which manifest through Fano antiresonances in the local density of states of the embedded quantum dot and normal transmission. This means that there is a correlation between Andreev bound states and Fano resonances that is robust under the influence of high electronic correlation. We have also found that the dominant couplings at the quantum dots are characterized by a crossover region that defines the range where the Fano-Kondo and the Andreev-Kondo effect prevail in each quantum dot. Likewise, we find that the interaction between Kondo and Andreev bound states has a notable influence on the Andreev transport.
An extended Hubbard model, including Coulomb repulsion and correlated hopping between nearest nei... more An extended Hubbard model, including Coulomb repulsion and correlated hopping between nearest neighbors, is studied using a mean field approach. Superconducting solutions are tested in the presence of antiferromagnetism, near to and away from half filling. Competition between on-site and intersite repulsions, modulated by correlated hopping, yields a covalent bond configuration with partial intrasite and intersite pairings. In addition, antiferromagnetism induces mixed sand p-type pairing, and superconductivity is completely suppressed by the saturation of the staggered magnetic moment.
... COVALENT BOND PAIRING IN AN EXTENDED HUBBARD MODEL 'WITH CORRELATED HOPPING INTERPLAY OF... more ... COVALENT BOND PAIRING IN AN EXTENDED HUBBARD MODEL 'WITH CORRELATED HOPPING INTERPLAY OF ANTIFERROMAGNETISM AND SUPERCONDUCTIVITY GALARA and GGCABRERA INSTITUTO DE FISICA GLEB WATAGHIN, UNIVERSIDADE ESTADUAL ...
We study the finite size effect of the Kondo screening cloud in a double-quantum-dot setup via a ... more We study the finite size effect of the Kondo screening cloud in a double-quantum-dot setup via a large-N slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size L and the other dot is side-coupled to the embedded dot via an antiferromagnetic spin-spin exchange coupling with the strength K. The antiferromagnetic coupling favors the local spin-singlet and suppresses the Kondo screening. The effective Kondo temperature T k (proptotional to the inverse of the Kondo screening cloud size) shows the Kosterlitz-Thouless (KT) scaling at finite sizes, indicating the quantum transition of the KT type between the Kondo screened phase for K ≤ Kc and the local spin-singlet phase for K ≥ Kc in the thermodynamic limit with Kc being the critical value. The mean-field phase diagram as a function of 1/L and K shows a crossover between Kondo and local spin-singlet ground states for K < Kc (L = 4n, 4n + 1, 4n + 3) and for K > Kc (L = 4n + 2). To look into the crossover region more closely, the local density of states on the quantum dot and the persistent current at finite sizes with different values of K are also calculated.
In this article, we study the quantum transport through a single-level quantum-dot in Kondo regim... more In this article, we study the quantum transport through a single-level quantum-dot in Kondo regime, coupled to current leads and embedded between two one-dimensional topological superconductors, each hosting Majorana zero modes at their ends. The Kondo effect in the quantum dot is modeled by mean-field finite-U auxiliary bosons approximation and solved by using the nonequilibrium Green's function approach. First, we calculate the density of states of the quantum dot, and then both the current and the differential conductance through the quantum dot in order to characterize the interplay between the Kondo resonance and Majorana zero modes. The results reveal that the presence of Majorana zero modes modifies the Kondo resonance exhibiting an anti-resonance structure in the density of states, leading to obtain spin-resolved behavior of the measurable current and differential conductance. We believe our findings could be helpful to understand the behavior of the Kondo effect in connection with Majorana zero modes.
We study the tunneling of electrons in semiconductor superlattices (SL) where the width of the ba... more We study the tunneling of electrons in semiconductor superlattices (SL) where the width of the barrier is modulated by a Gaussian function. The system is modelated using the effective mass approximation for the electrons and it is solved with the transfer-matrix method. We found, as in the previous models of Gaussian SL, that the probability of transmission is almost equal to unity in the miniband. In comparison with previous designs of SLs, our system shows experimental advantages.
Single electron transistors can be manufactured by coupling a Carbon Nanotubes (CNT) to metal lea... more Single electron transistors can be manufactured by coupling a Carbon Nanotubes (CNT) to metal leads. In this case the Kondo effect may arise. The difference between the Kondo effect in CNT and the same effect in quantum dots (QD) comes from the degeneracy of the chiral states of the CNT. While in QDs the Kondo effect is related to the
Electron tunneling through a double quantum dot molecule, in the Kondo regime, under the effect o... more Electron tunneling through a double quantum dot molecule, in the Kondo regime, under the effect of a magnetic field and an applied voltage, is studied. This system possesses a complex response to the applied fields characterized by a tristable solution for the conductance. The different nature of the solutions are studied in and out thermodynamical equilibrium. It is shown that the interdot coupling and the fields can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution of the problem.
We study transport of non-interacting electrons through two quantum dot molecules embedded in an ... more We study transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov-Bohm interferometer. The system in equilibrium exhibits bound states in the continuum (BIC) and total suppression of transmission. It also shows a magnetic flux-dependent effective level attraction and lines of perfect transmission when the intramolecular coupling is weak. Out of equilibrium, the current displays two kind of negative differential conductance (NDC) regions, which have different origins. One is generated by the usual mechanism of the NDC arising in a double quantum dot system. The other is induced by the magnetic flux, and it occurs at small voltages and for a well definite range of the intramolecular couplings. We explain this effect in terms of the level attraction displayed by the system.
Electron tunneling through a two stage Kondo system constituted by a double quantum-dot molecule ... more Electron tunneling through a two stage Kondo system constituted by a double quantum-dot molecule side coupled to a quantum wire, under the effect of a finite external potential is studied. We found that I-V characteristic shows a negative differential conductance region induced by the electronic correlation. This phenomenon is a consequence of the properties of the two stage Kondo regime under the effect of an external applied potential that takes the system out of equilibrium. The problem is solved using the mean-field finite-U slave-boson formalism.
In this work, we use three different numerical techniques to study the charge transport propertie... more In this work, we use three different numerical techniques to study the charge transport properties of a system in the two-level SU(2) (2LSU2) regime, obtained from an SU(4) model Hamiltonian by introducing orbital mixing of the degenerate orbitals via coupling to the leads. SU(4) Kondo physics has been experimentally observed, and studied in detail, in Carbon Nanotube Quantum Dots. Adopting a two molecular orbital basis, the Hamiltonian is recast into a form where one of the molecular orbitals decouples from the charge reservoir, although still interacting capacitively with the other molecular orbital. This basis transformation explains in a clear way how the charge transport in this system turns from double-to single-channel when it transitions from the SU(4) to the 2LSU2 regime. The charge occupancy of these molecular orbitals displays gate-potential-dependent occupancy oscillations that arise from a competition between the Kondo and Intermediate Valence states. The determination of whether the Kondo or the Intermediate Valence state is more favorable, for a specific value of gate potential, is assessed by the definition of an energy scale T0, which is calculated through DMRG. We speculate that the calculation of T0 may provide experimentalists with a useful tool to analyze correlated charge transport in many other systems. For that, a current work is underway to improve the numerical accuracy of its DRMG calculation and explore different definitions.
Physica E: Low-dimensional Systems and Nanostructures, 2010
ABSTRACT We study equilibrium and non-equilibrium transport of non-interacting electrons through ... more ABSTRACT We study equilibrium and non-equilibrium transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov–Bohm interferometer, and focus in several quantum interference effects occurring in both regimes. We obtain analytical expressions for the transmission and the density of states, and we calculate numerically the current at zero temperature. We show that the system exhibits Fano resonances, total suppression of transmission, and bound states in the continuum. In equilibrium we find a magnetic flux-dependent effective level attraction and lines of perfect transmission when the intramolecular coupling is weak. This feature has strong consequences in the non-equilibrium regime, where the I–V characteristics displays a region of negative differential conductance induced by the magnetic flux. The current suffers an abrupt rise for small bias voltages as consequence of an effective level attraction of the hybridized levels produced by the flux. The decrease of current is result of the destruction of this effect when the bias is increased.
We study transport through two quantum dot molecules embedded in an Aharonov-Bohm interferometer.... more We study transport through two quantum dot molecules embedded in an Aharonov-Bohm interferometer. We obtain analytically the conductance in equilibrium at zero temperature. As a result of quantum interference, this system exhibits up to two bound states in the continuum simultaneously, and remarkably maximum conductance occurs even when the molecules have both extremely weak interdot couplings.
Electron tunneling through a double quantum dot molecule side attached to a quantum wire, in the ... more Electron tunneling through a double quantum dot molecule side attached to a quantum wire, in the Kondo regime, is studied. The mean-field finite-U slave-boson formalism is used to obtain the solution of the problem. We investigate the many body molecular Kondo state and its interplay with the inter-dot antiferromagnetic correlation as a function of the parameters of the system.
The analysis of resonant tunneling through semiconductor superlattices (SLs) has a lot of interes... more The analysis of resonant tunneling through semiconductor superlattices (SLs) has a lot of interest whether from fundamental point of view as for its applications in microelectronic devices. Since the pioneering work of Esaki and Tsu [1], the transport properties of these structures have been intensely investigated experimentally and theoretically [2]. Due to advances in manufacturing techniques of semiconductor heterostructures, it is possible to tailor the band structure of SLs to the particular needs of every experiment. Recently, Tung and Lee [3] proposed a novel SL where the heights of the barrier and the bottom of the quantum wells are modulated by Gaussian functions. These authors found some plateaus in the transmission characteristic where electrons are almost un-scattered. This is very different at uniform SLs, where the transmission probability has great oscillations in each miniband. More recently, Gomez et al.[4] have reported similar effects SLs where only the heights of...
Physica E: Low-dimensional Systems and Nanostructures, 2003
Electron tunneling through a non-equilibrium double quantum dot in a series in the Kondo regime i... more Electron tunneling through a non-equilibrium double quantum dot in a series in the Kondo regime is studied. In the region of negative di erential resistance, it is shown that this system possesses a complex response to the applied potential characterized by a tristable solution for the current. The di erent natures of the solutions are characterized and it is shown that the e ects of an applied magnetic ÿeld could be used to control the region of tristability. The mean-ÿeld slave-boson formalism is used to obtain the solution of the problem.
Electron tunneling through a non-equilibrium double quantum dot in the Kondo regime is studied. I... more Electron tunneling through a non-equilibrium double quantum dot in the Kondo regime is studied. In the region of negative differential resistance, it is shown that this system possesses a complex response to the applied potential characterized by a tristable solution for the current. Increasing the applied potential or reducing the inter-dot coupling, the system goes through a transition from a coherent inter-dot regime to an incoherent one. The different nature of the solutions are characterized and it is shown that the effects of the asymmetry in the dot-lead coupling can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution of the problem.
We present a cluster effective-medium approach to the extended Hubbard model, for the zerotempera... more We present a cluster effective-medium approach to the extended Hubbard model, for the zerotemperature, half-filled-band paramagnetic phase. We recover the known limits and comment on the broadening corrections to the model, and find a first-order metal-insulator transition, resulting from both the cluster nature of the method and the correlated hopping term.
In the present work, we investigate the electronic transport through a T-shape double quantum dot... more In the present work, we investigate the electronic transport through a T-shape double quantum dot system coupled to two normal leads and to one superconducting lead. We explore the interplay between Kondo and Andreev states due to proximity effects. We find that Kondo resonance is modified by the Andreev bound states, which manifest through Fano antiresonances in the local density of states of the embedded quantum dot and normal transmission. This means that there is a correlation between Andreev bound states and Fano resonances that is robust under the influence of high electronic correlation. We have also found that the dominant couplings at the quantum dots are characterized by a crossover region that defines the range where the Fano-Kondo and the Andreev-Kondo effect prevail in each quantum dot. Likewise, we find that the interaction between Kondo and Andreev bound states has a notable influence on the Andreev transport.
An extended Hubbard model, including Coulomb repulsion and correlated hopping between nearest nei... more An extended Hubbard model, including Coulomb repulsion and correlated hopping between nearest neighbors, is studied using a mean field approach. Superconducting solutions are tested in the presence of antiferromagnetism, near to and away from half filling. Competition between on-site and intersite repulsions, modulated by correlated hopping, yields a covalent bond configuration with partial intrasite and intersite pairings. In addition, antiferromagnetism induces mixed sand p-type pairing, and superconductivity is completely suppressed by the saturation of the staggered magnetic moment.
... COVALENT BOND PAIRING IN AN EXTENDED HUBBARD MODEL 'WITH CORRELATED HOPPING INTERPLAY OF... more ... COVALENT BOND PAIRING IN AN EXTENDED HUBBARD MODEL 'WITH CORRELATED HOPPING INTERPLAY OF ANTIFERROMAGNETISM AND SUPERCONDUCTIVITY GALARA and GGCABRERA INSTITUTO DE FISICA GLEB WATAGHIN, UNIVERSIDADE ESTADUAL ...
We study the finite size effect of the Kondo screening cloud in a double-quantum-dot setup via a ... more We study the finite size effect of the Kondo screening cloud in a double-quantum-dot setup via a large-N slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size L and the other dot is side-coupled to the embedded dot via an antiferromagnetic spin-spin exchange coupling with the strength K. The antiferromagnetic coupling favors the local spin-singlet and suppresses the Kondo screening. The effective Kondo temperature T k (proptotional to the inverse of the Kondo screening cloud size) shows the Kosterlitz-Thouless (KT) scaling at finite sizes, indicating the quantum transition of the KT type between the Kondo screened phase for K ≤ Kc and the local spin-singlet phase for K ≥ Kc in the thermodynamic limit with Kc being the critical value. The mean-field phase diagram as a function of 1/L and K shows a crossover between Kondo and local spin-singlet ground states for K < Kc (L = 4n, 4n + 1, 4n + 3) and for K > Kc (L = 4n + 2). To look into the crossover region more closely, the local density of states on the quantum dot and the persistent current at finite sizes with different values of K are also calculated.
In this article, we study the quantum transport through a single-level quantum-dot in Kondo regim... more In this article, we study the quantum transport through a single-level quantum-dot in Kondo regime, coupled to current leads and embedded between two one-dimensional topological superconductors, each hosting Majorana zero modes at their ends. The Kondo effect in the quantum dot is modeled by mean-field finite-U auxiliary bosons approximation and solved by using the nonequilibrium Green's function approach. First, we calculate the density of states of the quantum dot, and then both the current and the differential conductance through the quantum dot in order to characterize the interplay between the Kondo resonance and Majorana zero modes. The results reveal that the presence of Majorana zero modes modifies the Kondo resonance exhibiting an anti-resonance structure in the density of states, leading to obtain spin-resolved behavior of the measurable current and differential conductance. We believe our findings could be helpful to understand the behavior of the Kondo effect in connection with Majorana zero modes.
We study the tunneling of electrons in semiconductor superlattices (SL) where the width of the ba... more We study the tunneling of electrons in semiconductor superlattices (SL) where the width of the barrier is modulated by a Gaussian function. The system is modelated using the effective mass approximation for the electrons and it is solved with the transfer-matrix method. We found, as in the previous models of Gaussian SL, that the probability of transmission is almost equal to unity in the miniband. In comparison with previous designs of SLs, our system shows experimental advantages.
Single electron transistors can be manufactured by coupling a Carbon Nanotubes (CNT) to metal lea... more Single electron transistors can be manufactured by coupling a Carbon Nanotubes (CNT) to metal leads. In this case the Kondo effect may arise. The difference between the Kondo effect in CNT and the same effect in quantum dots (QD) comes from the degeneracy of the chiral states of the CNT. While in QDs the Kondo effect is related to the
Electron tunneling through a double quantum dot molecule, in the Kondo regime, under the effect o... more Electron tunneling through a double quantum dot molecule, in the Kondo regime, under the effect of a magnetic field and an applied voltage, is studied. This system possesses a complex response to the applied fields characterized by a tristable solution for the conductance. The different nature of the solutions are studied in and out thermodynamical equilibrium. It is shown that the interdot coupling and the fields can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution of the problem.
We study transport of non-interacting electrons through two quantum dot molecules embedded in an ... more We study transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov-Bohm interferometer. The system in equilibrium exhibits bound states in the continuum (BIC) and total suppression of transmission. It also shows a magnetic flux-dependent effective level attraction and lines of perfect transmission when the intramolecular coupling is weak. Out of equilibrium, the current displays two kind of negative differential conductance (NDC) regions, which have different origins. One is generated by the usual mechanism of the NDC arising in a double quantum dot system. The other is induced by the magnetic flux, and it occurs at small voltages and for a well definite range of the intramolecular couplings. We explain this effect in terms of the level attraction displayed by the system.
Electron tunneling through a two stage Kondo system constituted by a double quantum-dot molecule ... more Electron tunneling through a two stage Kondo system constituted by a double quantum-dot molecule side coupled to a quantum wire, under the effect of a finite external potential is studied. We found that I-V characteristic shows a negative differential conductance region induced by the electronic correlation. This phenomenon is a consequence of the properties of the two stage Kondo regime under the effect of an external applied potential that takes the system out of equilibrium. The problem is solved using the mean-field finite-U slave-boson formalism.
In this work, we use three different numerical techniques to study the charge transport propertie... more In this work, we use three different numerical techniques to study the charge transport properties of a system in the two-level SU(2) (2LSU2) regime, obtained from an SU(4) model Hamiltonian by introducing orbital mixing of the degenerate orbitals via coupling to the leads. SU(4) Kondo physics has been experimentally observed, and studied in detail, in Carbon Nanotube Quantum Dots. Adopting a two molecular orbital basis, the Hamiltonian is recast into a form where one of the molecular orbitals decouples from the charge reservoir, although still interacting capacitively with the other molecular orbital. This basis transformation explains in a clear way how the charge transport in this system turns from double-to single-channel when it transitions from the SU(4) to the 2LSU2 regime. The charge occupancy of these molecular orbitals displays gate-potential-dependent occupancy oscillations that arise from a competition between the Kondo and Intermediate Valence states. The determination of whether the Kondo or the Intermediate Valence state is more favorable, for a specific value of gate potential, is assessed by the definition of an energy scale T0, which is calculated through DMRG. We speculate that the calculation of T0 may provide experimentalists with a useful tool to analyze correlated charge transport in many other systems. For that, a current work is underway to improve the numerical accuracy of its DRMG calculation and explore different definitions.
Physica E: Low-dimensional Systems and Nanostructures, 2010
ABSTRACT We study equilibrium and non-equilibrium transport of non-interacting electrons through ... more ABSTRACT We study equilibrium and non-equilibrium transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov–Bohm interferometer, and focus in several quantum interference effects occurring in both regimes. We obtain analytical expressions for the transmission and the density of states, and we calculate numerically the current at zero temperature. We show that the system exhibits Fano resonances, total suppression of transmission, and bound states in the continuum. In equilibrium we find a magnetic flux-dependent effective level attraction and lines of perfect transmission when the intramolecular coupling is weak. This feature has strong consequences in the non-equilibrium regime, where the I–V characteristics displays a region of negative differential conductance induced by the magnetic flux. The current suffers an abrupt rise for small bias voltages as consequence of an effective level attraction of the hybridized levels produced by the flux. The decrease of current is result of the destruction of this effect when the bias is increased.
We study transport through two quantum dot molecules embedded in an Aharonov-Bohm interferometer.... more We study transport through two quantum dot molecules embedded in an Aharonov-Bohm interferometer. We obtain analytically the conductance in equilibrium at zero temperature. As a result of quantum interference, this system exhibits up to two bound states in the continuum simultaneously, and remarkably maximum conductance occurs even when the molecules have both extremely weak interdot couplings.
Electron tunneling through a double quantum dot molecule side attached to a quantum wire, in the ... more Electron tunneling through a double quantum dot molecule side attached to a quantum wire, in the Kondo regime, is studied. The mean-field finite-U slave-boson formalism is used to obtain the solution of the problem. We investigate the many body molecular Kondo state and its interplay with the inter-dot antiferromagnetic correlation as a function of the parameters of the system.
The analysis of resonant tunneling through semiconductor superlattices (SLs) has a lot of interes... more The analysis of resonant tunneling through semiconductor superlattices (SLs) has a lot of interest whether from fundamental point of view as for its applications in microelectronic devices. Since the pioneering work of Esaki and Tsu [1], the transport properties of these structures have been intensely investigated experimentally and theoretically [2]. Due to advances in manufacturing techniques of semiconductor heterostructures, it is possible to tailor the band structure of SLs to the particular needs of every experiment. Recently, Tung and Lee [3] proposed a novel SL where the heights of the barrier and the bottom of the quantum wells are modulated by Gaussian functions. These authors found some plateaus in the transmission characteristic where electrons are almost un-scattered. This is very different at uniform SLs, where the transmission probability has great oscillations in each miniband. More recently, Gomez et al.[4] have reported similar effects SLs where only the heights of...
Physica E: Low-dimensional Systems and Nanostructures, 2003
Electron tunneling through a non-equilibrium double quantum dot in a series in the Kondo regime i... more Electron tunneling through a non-equilibrium double quantum dot in a series in the Kondo regime is studied. In the region of negative di erential resistance, it is shown that this system possesses a complex response to the applied potential characterized by a tristable solution for the current. The di erent natures of the solutions are characterized and it is shown that the e ects of an applied magnetic ÿeld could be used to control the region of tristability. The mean-ÿeld slave-boson formalism is used to obtain the solution of the problem.
Electron tunneling through a non-equilibrium double quantum dot in the Kondo regime is studied. I... more Electron tunneling through a non-equilibrium double quantum dot in the Kondo regime is studied. In the region of negative differential resistance, it is shown that this system possesses a complex response to the applied potential characterized by a tristable solution for the current. Increasing the applied potential or reducing the inter-dot coupling, the system goes through a transition from a coherent inter-dot regime to an incoherent one. The different nature of the solutions are characterized and it is shown that the effects of the asymmetry in the dot-lead coupling can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution of the problem.
We present a cluster effective-medium approach to the extended Hubbard model, for the zerotempera... more We present a cluster effective-medium approach to the extended Hubbard model, for the zerotemperature, half-filled-band paramagnetic phase. We recover the known limits and comment on the broadening corrections to the model, and find a first-order metal-insulator transition, resulting from both the cluster nature of the method and the correlated hopping term.
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Papers by Gustavo Lara