arXiv subjects

D. Zambrano

Publications and source records attributed to D. Zambrano.

11 recordsLinked to original sources

arXiv2026

Effects of random vacancies on the spin-dependent thermoelectric properties of silicene nanoribbon

The spin-dependent thermoelectric properties of silicene nanoribbon heterostructures are investigated, in which the central conductor contains a random distribution of vacancies and is connected to two pristine leads of the same material, placed in proximity to ferromagnetic insulators. The magnetic moments of the leads are analyzed in both parallel and antiparallel configurations. A tight-binding Hamiltonian and the Green's function formalism are employed to calculate the spin-resolved thermoelectric properties of the system as functions of geometrical confinement and vacancy concentration. The results demonstrate an enhancement in charge and spin-dependent thermopower, resulting in an improved thermoelectric efficiency at room temperature, which overcomes the limitations imposed by the classical Wiedemann-Franz law. These findings indicate that defective silicene nanoribbons are promising platforms for the development of efficient thermoelectric and spin-caloritronic devices.

cond-mat.mes-hall↗

arXiv2023

Bound states in the continuum and Majorana zero modes in a double quantum dot interferometer: Ghost-Fano Majorana effect

We investigate the transport properties through a nanostructure composed of parallel double quantum dots coupled to two normal contacts. Additionally, each quantum dot is connected to a topological superconducting nanowire, hosting Majorana zero modes at its ends. A magnetic flux threading across the area enclosed by the interferometer is considered. First, we investigate the physical quantities of the system employing Green's function formalism. We find that the emergence of bound states appears in symmetric configurations of topological superconducting nanowires, i.e., depending on their lengths and coupling energies to the quantum dots. Also, we find a transport suppression anomaly as a function of the magnetic flux in the same symmetric configurations mentioned above. Besides, we find that the magnetic flux controls both the projection of Majorana zero modes and of the bound states in the continuum into the density of states and the linear conductance, suggesting that only by switching this parameter can we manipulate both bound states.

cond-mat.mes-hall↗

arXiv2022

Kondo effect in a quantum dot embedded between topological superconductors

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 non-equilibrium 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.

cond-mat.mes-hall↗

arXiv2021

Spin and valley filter based on two-dimensional WSe$_2$ heterostructures

In this work, we investigate spin and valley transport properties of a WSe$_2$ monolayer placed on top of a ferromagnetic insulator. We are interested in controlling the transport properties by applying external potentials to the system. To obtain spin an valley polarizations, we have considered a single and a double barrier structure with gate potentials. We have analyzed how the efficiency of these polarized transport properties depend on the gate-potential intensities and geometrical configurations. Additionally, we investigate how the spin and valley transport properties are modified when an ac-potential is applied to the system. We have obtained a controllable modulation of the spin and valley polarizations as a function of the intensity and frequency of the ac-potential, mainly in the terahertz range. These results validate the proposal of double quantum well structures of WSe$_2$ as candidates to provide spin and valley dependent transport within an optimal geometrical parameter regime.

cond-mat.mes-hall↗

arXiv2019

Quantum and classical Otto engine for a 2-D material: the case of a graphene quantum dot

In this work, we study the performance of classical and quantum magnetic Otto cycles with a working substance composed of a single graphene quantum dot modeled by the continuum approach with the use of the zigzag boundary condition. Modulating an external/perpendicular magnetic field, in the classical approach, we found a constant behavior in the total work extracted that is not present in the quantum formulation. We find that, in the classical approach, the engine yielded a greater performance in terms of total work extracted and efficiency as compared with its quantum counterpart. In the classical case, this is due to the working substance being in thermal equilibrium at each point of the cycle, maximizing the energy extracted in the adiabatic strokes.

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↗

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↗

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

Finite-size corrections to scaling of the magnetization distribution in the $2d$ $XY$-model at zero temperature

The zero-temperature, classical $XY$-model on an $L \times L$ square-lattice is studied by exploring the distribution $Φ_L(y)$ of its centered and normalized magnetization $y$ in the large $L$ limit. An integral representation of the cumulant generating function, known from earlier works, is used for the numerical evaluation of $Φ_L(y)$, and the limit distribution $Φ_{L \rightarrow \infty} (y) = Φ_0(y)$ is obtained with high precision. The two leading finite-size corrections $Φ_L (y) -Φ_0 (y) \approx a_1(L)\, Φ_1(y) + a_2(L)\,Φ_2(y)$ are also extracted both from numerics and from analytic calculations. We find that the amplitude $a_1(L)$ scales as $\ln(L/L_0) /L^2$ and the shape correction function $Φ_1 (y)$ can be expressed through the low-order derivatives of the limit distribution, $Φ_1 (y) = [\,y\, Φ_0 (y) + Φ'_0 (y)\,]'$. The second finite-size correction has an amplitude $a_2(L)\propto 1/L^2$ and one finds that $a_2\,Φ_2(y) \ll a_1 \,Φ_1(y)$ already for small system size ($L> 10$). We illustrate the feasibility of observing the calculated finite-size corrections by performing simulations of the $XY$-model at low temperatures, including $T = 0$.

cond-mat.stat-mech↗

arXiv2009

Analytical computation of the magnetization probability density function for the harmonic 2D XY model

The probability density function (PDF) of some global average quantity plays a fundamental role in critical and highly correlated systems. We explicitly compute this quantity as a function of the magnetization for the two dimensional XY model in its harmonic approximation. Numerical simulations and perturbative results have shown a Gumbel-like shape of the PDF, in spite of the fact that the average magnetization is not an extreme variable. Our analytical result allows to test both perturbative analytical expansions and also numerical computations performed previously. Perfect agreement is found for the first moments of the PDF. Also for large volume and in the high temperature limit the distribution becomes Gaussian, as it should be. In the low temperature regime its numerical evaluation is compatible with a Gumbel distribution.

hep-lat↗

arXiv2009

Cluster Algorithm Renormalization Group Study of Universal Fluctuations in the 2D Ising Model

In this paper we propose a novel method to study critical systems numerically by a combined collective-mode algorithm and Renormalization Group on the lattice. This method is an improved version of MCRG in the sense that it has all the advantages of cluster algorithms. As an application we considered the 2D Ising model and studied wether scale invariance or universality are possible underlying mechanisms responsible for the approximate "universal fluctuations" close to a so-called bulk temperature $T^*(L)$. "Universal fluctuations" was first proposed in [1] and stated that the probability density function of a global quantity for very dissimilar systems, like a confined turbulent flow and a 2D magnetic system, properly normalized to the first two moments, becomes similar to the "universal distribution", originally obtained for the magnetization in the 2D XY model in the low temperature region. The results for the critical exponents and the renormalization group flow of the probability density function are very accurate and show no evidence to support that the approximate common shape of the PDF should be related to both scale invariance or universal behavior.

cond-mat.stat-mech↗