arXiv subjects

P. A. Orellana

Publications and source records attributed to P. A. Orellana.

At least 37 records · Page 2Linked to original sources

arXiv2019

Majorana bound state in the continuum: Coupling between Majorana bound state and quantum dot mediated by continuum

In this work, we consider a single-level quantum dot (QD) and a Majorana bound state (MBS) placed at the end of a topological superconducting nanowire (TSW). Both are coupled to the continuum and do not have a direct connection between them. We addressed the behavior of MBS leaking phenomena and its consequences into the QD physics in non-interacting and Coulomb blockade regime. By employing Green's function formalism via the equation of motion procedure, we calculate the physical quantities of interest. Our results show that the leakage of the MBS into the continuum state is achieved and can alter the physics of Coulomb blockade in the system through continuum-mediated coupling between MBS and QD. As a main consequence, we found a robust and non-trivial mechanism to accomplish a bound state in the continuum in the system.

cond-mat.mes-hall↗

arXiv2019

Fano-Majorana effect and bound states in the continuum on a crossbar-shaped quantum dot hybrid structure

We investigate transport properties through a crossbar-shaped structure formed by a quantum dot (QD) coupled to two normal leads and embedded between two one-dimensional topological superconductors (TSCs). Each TSC hosts Majorana bound states (MBSs) at its ends, which can interact between them with an effective coupling strength. We find a signature of bound states in continuum (BIC) in the MBSs spectral function. By allowing finite inter MBSs coupling, BICs splitting is observed and shows projection in transmission for asymmetric coupling case as cuasi-BICs. As a consequence, we also show that the Fano effect, arising from interference phenomena between MBSs hybridization trough QD, is observed with a half-integer amplitude modulation. We believe our findings can help to better understand the properties of MBSs and their interplay with QDs.

cond-mat.mes-hall↗

arXiv2019

Tunable spin-polarized edge currents in proximitized transition metal dichalcogenides

We explore proximity-induced ferromagnetism on transition metal dichalcogenide (TMD), focusing on molybdenum ditelluride (MoTe$_{2}$) ribbons with zigzag edges, deposited on ferromagnetic europium oxide (EuO). A three-orbital tight-binding model incorporates the exchange and Rashba fields induced by proximity to the EuO substrate. For in-gap Fermi levels, electronic modes in the nanoribbon are strongly spin-polarized and localized along the edges, acting as one-dimensional (1D) conducting channels with tunable spin-polarized currents. Hybrid structures such as the MoTe$_{2}$/EuO configuration can serve as building blocks for spintronic devices, and provide versatile platforms to further understand proximity effects in diverse materials systems.

cond-mat.mes-hall↗

arXiv2019

A tunable single photon quantum router

We propose an efficient single-photon router comprising two resonator waveguide channels coupled by several sequential cavities with embedded three-level atoms. We show that the system can operate as a perfect four-way single-photon switch. We also demonstrate that an incident single-photon propagating in one of the waveguides can be routed into one or the other output channels; such routing can be controlled by the external classical electromagnetic field driving the atoms. We argue that, under appropriate conditions, the efficiency of such routing can be close to 100\% within a broad operational bandwidth, suggesting various applications in photonics.

quant-ph↗

arXiv2018

Bound states in the continuum poisoned by Majorana fermions

In this work, we study the bound states in the continuum (BICs) in a system formed by a triple quantum dot array embedded between two one-dimensional topological superconductors, both hosting Majorana bound states (MBSs) at its ends. The results show the formation of BICs with topological characteristics due to the presence of MBSs. The latter is a consequence of the interplay between the BIC arising from quantum dots states by means of energy level symmetry breaking through gate voltages, and MBSs leaked into the quantum dots. The BIC is not observed when both TSCs are in long wire limit, i. e. for vanishing inter MBSs coupling, while it projects into the electronic transmission whenever the inter MBSs couplings are away from zero, regardless if they are different and/or the phase difference between both TSCs. We study the behavior of BICs poisoned by MBSs as a function of the parameters that are controlling the system. We believe our findings could be useful to implement a protection tool for BICs using MBSs based on tunable gate voltages.

cond-mat.mes-hall↗

arXiv2018

Enhancement of the thermoelectric efficiency in a T-shaped quantum dot system in the linear and nonlinear regimes

In the present work, we investigate the thermoelectric properties of a T-shaped double quantum dot system coupled to two metallic leads incorporating the intra-dot Coulomb interaction. We explore the role of the interference effects and Coulomb blockade on the thermoelectric efficiency of the system in the linear and nonlinear regimes. We studied as well the effect of a Van-Hove singularity of the leads density of states (DOS) at the neighborhood of the Fermi energy, a situation that can be obtained using a carbon nanotube, a graphene nano-ribbon or other contacts with one-dimensional properties. The system is studied above the Kondo temperature. The Coulomb blockade of the electronic charges is studied using the Hubbard III approximation, which properly describes the transport properties of this regime. In the linear response, our results show an enhancement of the thermopower and the figure of merit of the system. For a nonlinear situation, we calculate the thermoelectric efficiency and power output, concluding that the T-shaped double quantum dot is an efficient thermoelectric device. Moreover, we demonstrate the great importance of the DOS Van-Hove singularity at the neighborhood of the Fermi energy to obtain a very significant increase of the thermoelectric efficiency of the system.

cond-mat.mes-hall↗

arXiv2017

Spin-Seebeck effect and spin polarization in a multiple quantum dot molecule

In this work, we study the conductance and the thermoelectric properties of a quantum dot embedded between two metallic leads with a side-coupled triple quantum dot molecule under a magnetic field. We focus on the spin polarization and thermoelectric quantities. Our results show the possibility of design an efficient spin filter device besides a noticeable enhancement of the Seebeck coefficient driven by the asymmetry in the quantum dots energy levels and a tunable pure spin Seebeck effect is obtained. This behavior also holds in the interacting case, where a pure spin Seebeck effect can be obtained for fixed values of the embedded quantum dot energy level. Our findings could lead to the implementation of a new pure spin energy conversion and capable spin filter devices working with weak magnetic fields.

cond-mat.mes-hall↗

arXiv2017

Stacking change in MoS$_{2}$ bilayers induced by interstitial Mo impurities

We use a theoretical approach to reveal the electronic and structural properties of molybdenum impurities between MoS$_{2}$ bilayers. We find that interstitial Mo impurities are able to reverse the well-known stability order of the pristine bilayer, because the most stable form of stacking changes from AA' (undoped) into AB (doped). The occurrence of Mo impurities in different positions shows their split electronic levels in the energy gap, following octahedral and tetrahedral crystal fields. The energy stability is related to the accommodation of Mo impurities compacted in hollow sites between layers. Other less stable configurations for Mo dopants have larger interlayer distances and band gaps than those for the most stable stacking. Our findings suggest possible applications such as exciton trapping in layers around impurities, and the control of bilayer stacking by Mo impurities in the growth process.

cond-mat.mtrl-sci↗

arXiv2017

Spin and charge caloritronics in bilayer graphene flakes with magnetic contacts

We investigate the coupling of spin and thermal currents as a means to rise the thermoelectric efficiency of nanoscale graphene devices. We consider nanostructures composed of overlapping graphene nanoribbons with ferromagnetic contacts in different magnetic configurations. Our results show that the charge Seebeck effect is greatly enhanced when the magnetic leads are in an antiparallel configuration, due to the enlargement of the transport gap. However, for the optimization of the charge figure of merit ZT it is better to choose a parallel alignment of the magnetization in the leads, because the electron-hole symmetry is broken in this magnetic configuration. We also obtain the spin-dependent Seebeck coefficient and spin figure of merit. In fact, the spin ZT can double its value with respect to the charge ZT for a wide temperature range, above 300 K. These findings suggest the potential value of graphene nanosystems as energy harvesting devices employing spin currents.

cond-mat.mes-hall↗

arXiv2017

Spin-polarized electric current in silicene nanoribbons induced by atomic adsorption

We investigate the nonequilibrium transport properties of a silicene armchair nanoribbon with a random distribution of adsorbed atoms in apex positions. A ferromagnetic insulator grown below the nanoribbon splits spin-up and spin-down electron bands and gives rise to a spin polarization of the conductance. The conductance vanishes when the Fermi energy matches the adatom levels due to the coupling of adatom localized states with the continuum spectra of the nanoribbon. This is the well-known Fano effect, resulting in a spin-dependent antiresonance in the conductance. The different antiresonance energies of spin-up and spin-down electrons give rise to a full spin polarization of the conductance in a broad energy window. This spin-dependent Fano effect opens the possibility to using it in spintronics as a tuneable source of polarized electrons.

cond-mat.mes-hall↗

arXiv2017

Detecting coupling of Majorana bound states with an Aharonov-Bohm interferometer

We study the transport properties of an interferometer composed by a quantum dot (QD) coupled with two normal leads and two one-dimensional topological superconductor nanowires (TNWs) hosting Majorana bound states (MBS) at their ends. The geometry considered is such that one TNW has both ends connected with the QD, forming an Aharonov-Bohm (AB) interferometer threaded by an external magnetic flux, while the other TNW is placed near the interferometer TNW. This geometry can alternatively be seen as a long wire contacted across a local defect, with possible coupling between independent-MBS. We use the Green's function formalism to calculate the conductance across normal current leads on the QD. We find that the conductance exhibits a half-quantum value regardless of the AB phase and location of the dot energy level, whenever the interferometer configuration interacts with the neighboring TNW. These findings suggest that such a geometry could be used for a sensitive detection of MBS interactions across TNWs, exploiting the high sensitivity of conductance to the AB phase in the interferometer.

cond-mat.mes-hall↗

arXiv2016

Photon-assisted transport in bilayer graphene flakes

The electronic conductance of graphene-based bilayer flake systems reveal different quantum interference effects, such as Fabry-Pérot resonances and sharp Fano antiresonances on account of competing electronic paths through the device. These properties may be exploited to obtain spin-polarized currents when the same nanostructure is deposited above a ferromagnetic insulator. Here we study how the spin-dependent conductance is affected when a time-dependent gate potential is applied to the bilayer flake. Following a Tien-Gordon formalism we explore how to modulate the transport properties of such systems via appropriate choices of the $ac$-field gate parameters. The presence of the oscillating field opens the possibility of tuning the original antiresonances for a large set of field parameters. We show that interference patterns can be partially or fully removed by the time-dependent gate voltage. The results are reflected in the corresponding weighted spin polarization which can reach maximum values for a given spin component. We found that differential conductance maps as functions of bias and gate potentials show interference patterns for different $ac$-field parameter configurations. The proposed bilayer graphene flake systems may be used as a frequency detector in the THz range.

cond-mat.mes-hall↗

arXiv2016

Fano-Andreev effect in T-shape double-quantum-dot in the Kondo regime

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.

cond-mat.mes-hall↗

arXiv2016

Thermoelectric transport through Majorana bound states and violation of Wiedemann-Franz law

We study features of the thermoelectric transport through a Kitaev chain hosting Majorana bound states (MBS) at its ends. We describe the behavior of the Seebeck coefficient and the ZT figure of merit for two different configurations between MBS and normal current leads. We find an important violation of the Wiedemann-Franz law in one of these geometries, leading to sizeable values of the thermoelectric efficiency over a narrow window in chemical potential away from neutrality. These findings could lead to interesting thermoelectric-based MBSs detection devices, via measurements of the Seebeck coefficient and figure of merit.

cond-mat.mes-hall↗

arXiv2015

Enhancing thermoelectric properties of graphene quantum rings

We study the thermoelectric properties of rectangular graphene rings connected symmetrically or asymmetrically to the leads. A side-gate voltage applied across the ring allows for the precise control of the electric current flowing through the system. The transmission coefficient of the rings manifests Breit-Wigner line-shapes and/or Fano line-shapes, depending on the connection configuration, the width of nanoribbons forming the ring and the side-gate voltage. We find that the thermopower and the figure of merit are greatly enhanced when the chemical potential is tuned close to resonances. Such enhancement is even more pronounced in the vicinity of Fano like anti-resonances which can be induced by a side-gate voltage independently of the geometry. This opens a possibility to use the proposed device as a tunable thermoelectric generator.

cond-mat.mes-hall↗

arXiv2014

Interference effects induced by Andreev bound states in a hybrid nanostructure composed by a quantum dot coupled to ferromagnetic and superconductor leads

In this work, it is considered a nanostructure composed by a quantum dot coupled to two ferromagnets and a superconductor. The transport properties of this system are studied within a generalized mean-field approximation taking into account proximity effects and spin-flip correlations within the quantum dot. It is shown that the zero-bias transmittance for the co-tunneling between the ferromagnetic leads presents a dip whose height depends on the relative orientation of the magnetizations. When the superconductor is coupled to the system, electron-hole correlations between different spin states leads to a resonance in the place of the dip appearing in the transmittance. Such an effect is accompanied by two anti-resonances explained by a leakage of conduction channels from the co-tunneling to the Andreev transport. In the non-equilibrium regime, correlations within the quantum dot introduce a dependence of the resonance condition on the finite bias applied to the ferromagnetic leads. However, it is still possible to observe signatures of the same interference effect in the electrical current.

cond-mat.mes-hall↗

arXiv2014

Bound states in the continuum: localization of Dirac-like fermions

We report the formation of bound states in the continuum for Dirac-like fermions in structures composed by a trilayer graphene flake connected to nanoribbon leads. The existence of this kind of localized states can be proved by combining local density of states and electronic conductance calculations. By applying a gate voltage, the bound states couple to the continuum, yielding a maximum in the electronic transmission. This feature can be exploited to identify bound states in the continuum in graphene-based structures.

cond-mat.mes-hall↗

arXiv2014

Single-parameter spin-pumping in driven metallic rings with spin-orbit coupling

We consider the generation of a pure spin-current at zero bias voltage with a single time-dependent potential. To such end we study a device made of a mesoscopic ring connected to electrodes and clarify the interplay between a magnetic flux, spin-orbit coupling and non-adiabatic driving in the production of a spin and electrical current. By using Floquet theory, we show that the generated spin to charge current ratio can be controlled by tuning the spin-orbit coupling.

cond-mat.mes-hall↗