arXiv subjects

Emmanuel Pereira

Publications and source records attributed to Emmanuel Pereira.

At least 19 recordsLinked to original sources

arXiv2023

Heat Current Properties of a Rotor Chain Type Model with Next-Nearest-Neighbor Interactions

In this article, to study the heat flow behavior, we perform analytical investigations in a rotor chain type model (involving inner stochastic noises) with next and next-nearest-neighbor interactions. It is known in the literature that the chain rotor model with long range interactions presents an insulating phase for the heat conductivity. But we show, in contrast with such a behavior, that the addition of a next-nearest-neighbor potential increases the thermal conductivity, at least in the low temperature regime, indicating that the insulating property is a genuine long range interaction effect. We still establish, now by numerical computations, the existence of a thermal rectification in systems with graded structures.

math-ph↗

arXiv2022

Non-trivial effect of dephasing: Enhancement of rectification of spin current in graded XX chains

In order to reveal mechanisms to control and manipulate spin currents, we perform a detailed investigation of the dephasing effects in the open XX model with a Lindblad dynamics involving global dissipators and thermal baths. Specifically, we consider dephasing noise modelled by current preserving Lindblad dissipators acting on graded versions of these spin systems, that is, systems in which the magnetic field and/or the spin interaction are growing (decreasing) along the chain. In our analysis, we study the non-equilibrium steady-state via the covariance matrix using the Jordan-Wigner approach to compute the spin currents. We find that the interplay between dephasing and graded systems gives rise to a non trivial behavior: when we have homogeneous magnetic field and graded interactions we have rectification enhancement mechanims, and when we have fully graded system we can control the spin current in order to keep the direction of the particle/spin flow even with inverted baths. We describe our result in detailed numerical analisys and we see that rectification in this simple model indicates that the phenomenon may be of general occurrence in quantum spin systems.

cond-mat.mes-hall↗

arXiv2020

Heat rectification on the XX chain

In order to better understand the minimal ingredients for thermal rectification, we perform a detailed investigation of a simple spin chain, namely, the open XX model with a Lindblad dynamics involving global dissipators. We use a Jordan-Wigner transformation to derive a mathematical formalism to compute the heat currents and other properties of the steady state. We have rigorous results to prove the occurrence of thermal rectification even for slightly asymmetrical chains. Interestingly, we describe cases where the rectification does not decay to zero as we increase the system size, that is, the rectification remains finite in the thermodynamic limit. We also describe some numerical results for more asymmetrical chains. The presence of thermal rectification in this simple model indicates that the phenomenon is of general occurrence in quantum spin systems.

quant-ph↗

arXiv2020

Rectification induced by geometry in two-dimensional quantum spin lattices

We address the role of geometrical asymmetry in the occurrence of spin rectification in two-dimensional quantum spin chains subject to two reservoirs at the boundaries, modeled by quantum master equations. We discuss the differences in the rectification for some one-dimensional cases, and present numerical results of the rectification coefficient R for different values of the anisotropy parameter of the XXZ model, and different configurations of boundary drives, including both local and non-local dissipators. Our results also show that geometrical asymmetry, along with inhomogeneous magnetic fields, can induce spin current rectification even in the XX model, indicating that the phenomenon of rectification due to geometry may be of general occurrence in quantum spin systems.

quant-ph↗

arXiv2020

Transport in boundary-driven quantum spin systems: One-way street for the energy current

We study transport properties in boundary-driven asymmetric quantum spin chains given by $\mathit{XXZ}$ and $\mathit{XXX}$ Heisenberg models. Our approach exploits symmetry transformations in the Lindblad master equation associated to the dynamics of the systems. We describe the mathematical steps to build the unitary transformations related to the symmetry properties. For general target polarizations, we show the occurrence of the one-way street phenomenon for the energy current, namely, the energy current does not change in magnitude and direction as we invert the baths at the boundaries. We also analyze the spin current in some situations, and we prove the uniqueness of the steady state for all investigated cases. Our results, involving nontrivial properties of the energy flow, shall interest researchers working on the control and manipulation of quantum transport.

quant-ph↗

arXiv2020

Beyond the Lindblad Master Equation: Heat, Work and Energy Currents in Boundary Driven Spin Chains

We consider the accurate investigation of the energy current and its components, heat and work, in some boundary driven quantum spin systems. The expressions for the currents, as well as the associated Lindblad master equation, are obtained via a repeated interaction scheme. We consider small systems in order to analytically compute the steady distribution to study the current in the steady state. Asymmetrical XXZ and quantum Ising models are detailed analyzed. For the XXZ chain we present cases in which different compositions of heat and work currents, obtained via the repeated interaction protocol, lead to the same energy current, which may be obtained via the Lindblad master equation. For the quantum Ising chain, we describe a case of zero energy current and novanishing heat and work currents. Our findings make clear that to talk about heat in these boundary driven spin quantum systems we must go beyond an investigation involving only the Lindblad master equation.

quant-ph↗

arXiv2020

Energy current manipulation and reversal of rectification in graded XXZ spin chains

This work is devoted to the investigation of nontrivial transport properties in many-body quantum systems. Precisely, we study transport in the steady state of spin-1/2 Heisenberg XXZ chains, driven out of equilibrium by two magnetic baths with fixed, different magnetization. We take graded versions of the model, i.e., asymmetric chains in which some structure gradually changes in space. We investigate how we can manipulate and control the energy and spin currents of such chains by tuning external and/or inner parameters. In particular, we describe the occurrence of energy current rectification and its reversal due to the application of external magnetic fields. We show that, after carefully chosen the inner parameters of the system, by turning on an external magnetic field we can find spin and energy currents propagating in different directions. More interestingly, we may find cases in which rectifications of the energy and of the spin currents occur in opposite directions, i.e., if the energy current is larger when flowing from left to right side, then the spin current is larger if it flows from the right to left side. We still describe situations with inversion of the energy current direction as we increase the system asymmetry. We stress that our work aims the development of theoretical knowledge as well as the stimulation of future experimental applications.

cond-mat.stat-mech↗

arXiv2020

One-way street for the energy current: A ubiquitous phenomenon in boundary-driven quantum spin chains

Focusing on the description of nontrivial properties of the energy transport at quantum scale, we investigate asymmetrical quantum spin chains described by boundary-driven $\mathit{XXZ}$ and $\mathit{XXX}$ Heisenberg models. We search for symmetries properties of the Lindblad master equation related to the dynamics of the system in order to establish properties of the steady state. Under rather general assumptions for the target polarization at the boundaries, we show the occurrence of an effect related to (but stronger than) energy rectification, namely, the one-way street phenomenon, which is the existence of an unique way for the energy flow. Precisely, the energy current does not change in magnitude and direction as we invert the baths at the boundaries: its direction is completely determined by the asymmetry in the bulk of the chain. The results follow independent of the system size and of the transport regime. Our findings show the ubiquitous occurrence of the one-way street phenomenon for the energy flow in boundary-driven spin systems and, we believe, they shall be an useful contribution to the area devoted to the investigation and building of efficient quantum devices used to control and manipulate the energy current.

quant-ph↗

arXiv2019

Thermal Rectification in Classical and Quantum Systems: Searching for Efficient Thermal Diodes

This mini-review addresses a bedrock problem for the advance of phononics: the building of feasible and efficient thermal diodes. We revisit investigations in classical and quantum systems. For the classical anharmonic chains of oscillators, the most used model for the study of heat conduction in insulating solids, we recall the ubiquitous occurrence of thermal rectification in graded systems, and we show that the match between graded structures and long range interactions is an efficient mechanism to increase the rectification factor. For the cases of genuine quantum models, we present the spin chains, such as the open $XXZ$ model, as profitable systems for the occurrence of thermal rectification and other interesting related properties. In particular, we describe two cases of perfect diodes: one for the spin current, in a two-segmented $XXZ$ model, and another one for the heat current in a simple quantum Ising model with long range interactions. We believe that such results involving interesting rectification properties in simple models will stimulate more theoretical and experimental investigations on the subject.

cond-mat.mes-hall↗

arXiv2019

Heat current rectification in segmented XXZ chains

We study the rectification of heat current in an XXZ chain segmented in two parts. We model the effect of the environment with Lindblad heat baths. We show that, in our system, rectification is large for strong interactions in half of the chain and if one bath is at cold enough temperature. For the numerically accessible chain lengths, we observe that the rectification increases with the system size. We gain insight in the rectification mechanism by studying two-time correlations in the steady state. The presence of interactions also induces a strong nonlinear response to the temperature difference, resulting in superlinear and negative differential conductance regimes.

cond-mat.stat-mech↗

arXiv2019

Perfect Thermal Rectification in a Many-Body Quantum Ising Model

We address a keystone problem for the progress of phononics: the proposal of efficient thermal diodes. Aiming the disclosure of an easy itinerary for the building of a heat rectifier, we investigate unsophisticated systems linked to simple thermal baths, precisely, asymmetric quantum Ising models, i.e., simple quadratic models, involving only one spin component. We analytically show the occurrence of thermal rectification for the case of a chain with interactions long enough to connect the first to the last site. Moreover, we describe cases of a perfect rectification, i.e., finite heat flow in one direction, and zero current in the opposite direction. We argue to indicate that the ingredients for the rectification are just given by the quantum nature of the baths and dynamics, and by the structural asymmetry of the system, here in the inter-site interactions. We believe that the description of a perfect thermal rectification in a simple many-body quantum model, that is, the presentation of a simple itinerary for the building of a diode shall stimulate theoretical and experimental research on the theme.

quant-ph↗

arXiv2018

Heat, Work and Energy Currents in the Boundary-Driven XXZ Spin Chain

We address the detailed study of the energy current and its components, heat and work, in the boundary-driven 1D XXZ quantum model. We carry out the investigation by considering two different approaches present in the literature. First, we take the repeated interaction scheme and derive the expressions for the currents of heat and work, exchanged between system and baths. Then, we perform the derivation of the energy current by means of a Lindblad master equation together with a continuity equation, another approach which is recurrently used. A comparison between the obtained expressions allows us to show the consistency of both approaches, and, in the latter expression derived from the Lindblad equation, it allows us to split the energy, which comes from the baths to the system, into heat and work. The recognition of work in the process, that is recurrently ignored in studies of transport, enables us to understand thermodynamical aspects and to solve some imbroglios in the physics behind the energy current in the XXZ spin chain.

cond-mat.stat-mech↗

arXiv2018

Perfect diode in quantum spin chains

We study the rectification of spin current in $XXZ$ chains segmented in two parts, each with a different anisotropy parameter. Using exact diagonalization and a matrix product states algorithm we find that a large rectification (of the order of $10^4$) is attainable even using a short chain of $N=8$ spins, when one half of the chain is gapless while the other has large enough anisotropy. We present evidence of diffusive transport when the current is driven in one direction and of a transition to an insulating behavior of the system when driven in the opposite direction, leading to a perfect diode in the thermodynamic limit. The above results are explained in terms of matching of spectrum of magnon excitations between the two halves of the chain.

cond-mat.stat-mech↗

arXiv2017

Rectification and One-Way Street for the Energy Current in Boundary-Driven Asymmetric Quantum Spin Chains

Motivated by the demand of efficient quantum devices to engineer the energy transport, we analyze some inhomogeneous quantum spin systems, including the XXZ chains, with magnetization baths at the ends. Aimed at finding general properties, we study the effects of suitable transformations on the boundary-driven Lindblad master equation associated to the dynamics of the systems. For asymmetric models with target polarization at the edges or twisted XY boundary gradients, we show properties of the steady state which establish features of the energy current, irrespective of the system size and of the regime of transport. We show the ubiquitous occurrence of energy rectification and, more interestingly, of an unusual phenomenon: in the absence of external magnetic field, there is an one-way street for the energy current, i.e., the direction of the energy current does not change as we invert the magnetization baths at the boundaries. Given the extensiveness of the procedures, which essentially involve properties of the Lindblad master equation, our results certainly follow for other interactions and other boundary conditions. Moreover, our results indicate graded spin chains as genuine quantum rectifiers.

quant-ph↗

arXiv2016

Energy Rectification in Quantum Graded Spin Chains: Analysis of the XXZ Model

In this work, with focus on the energy transport properties in quantum, low dimensional, graded materials, we address the investigation of the energy (and spin) current in XXZ open chains with graded inner structures and driven out of equilibrium by magnetization pumping applied at the ends. We study several types of graded structures in different situations in order to show a ubiquitous occurrence of energy rectification, even for the system under a homogeneous magnetic field. Due to technical difficulties, we carry out the computation for small chains, but we present arguments which indicate the extension of some results to larger systems. Recalling the generic existence of energy rectification in classical, graded materials, which are described by anharmonic chains of oscillators, and recalling also the anharmonicity of these XXZ models, which involve quartic terms in more transparent representation in terms of fermionic creation and annihilation operators, we may say that our results extend the ubiquity of energy rectification occurrence in classical graded materials to the case of quantum systems.

quant-ph↗

arXiv2015

Ingredients for an efficient thermal diode

We provide convincing empirical evidence that long range interactions strongly enhance the rectification effect which takes place in mass graded systems. Even more importantly the rectification does not decrease with the increase of the system size. Large rectification is obtained also for the equal mass case and with graded on-site potential. These results allow to overcome current limitations of the rectification mechanism and open the way for a realistic implementation of efficient thermal diodes.

cond-mat.stat-mech↗

arXiv2015

Heat flow in anharmonic crystals with internal and external stochastic baths: A convergent polymer expansion for a model with discrete time and long range interparticle interaction

We investigate a chain of oscillators with anharmonic on-site potentials, with long range interparticle interactions, and coupled both to external and internal stochastic thermal reservoirs of Ornstein-Uhlenbeck type. We develop an integral representation, a la Feynman-Kac, for the correlations and the heat current. We assume the approximation of discrete times in the integral formalism (together with a simplification in a subdominant part of the harmonic interaction) in order to develop a suitable polymer expansion for the model. In the regime of strong anharmonicity, strong harmonic pinning, and for the interparticle interaction with integrable polynomial decay, we prove the convergence of the polymer expansion uniformly in volume (number of sites and time). We also show that the two-point correlation decays in space such as the interparticle interaction. The existence of a convergent polymer expansion is of practical interest: it establishes a rigorous support for a perturbative analysis of the heat flow problem and for the computation of the thermal conductivity in related anharmonic crystals, including those with inhomogeneous potentials and long range interparticle interactions.

math-ph↗

arXiv2013

Increasing thermal rectification: Effects of long range interactions

In this paper, we study the effects of the interparticle interaction range on heat flow. We show that, by increasing the interaction range, we may amplify the thermal conductivity and even change the regime of heat transport. More importantly, considering a crucial problem of phononics, namely, the search of a suitable thermal diode, we investigate the range effects in some graded systems in which thermal rectification is a ubiquitous phenomenon. In such graded models, we show that long range interactions may significatively increase the rectification power and may avoid its decay with the system size, thus solving relevant problems of the usual proposals of rectifiers. Our results indicate that graded materials are genuine candidates for the actual fabrication of thermal diodes.

cond-mat.stat-mech↗