In this work we propose an electronic Lévy glass, analogous to a recent optical realization. To that end, we investigate the transmission of electrons in graphene nanoribbons in the presence of circular electrostatic clusters, whose diameter follow a power-law distribution. We analyze the effect of the electrostatic clusters on the electronic transport regime of the nanoribbons, in terms of its diffusion behavior. Our numerical calculations show that the presence of circular electrostatic clusters induces a transition from Lévy (superdiffusive) to diffusive transport as the energy increases. Furthermore, we argue that in our electronic Lévy glass, superdiffusive transport is an exclusive feature of the low-energy quantum regime, while diffusive transport is a feature of the semiclassical regime. We thus attribute the observed transition to the chiral symmetry breaking, once the energy moves away from the Dirac point of graphene.
The event will combine a set of lectures and research talks during the two weeks and will be a meeting point for researchers worldwide, nurturing collaborations and exchange of knowledge among researchers, students and postdocs of different continents and subfields. The activities will highlight recent progress in a range of topics including electronic hydrodynamics, dissipative systems and light-matter interaction, low-dimensional devices and disorder, topological materials, and emergent phases in novel materials.
It is my first in-person conference since February 2020, and I am very excited to participate in this amazing event. Many thanks to the support offered by ICTP and to the organization efforts led by Luis E. F. Foà Torres and collaborators.
In this publication we investigate the propagation of electronic waves in one-dimensional systems with Lévy-type disorder. We perform a complete analysis of nonrelativistic and relativistic wave transmission submitted to potential barriers whose width, separation, or both follow Lévy distributions characterized by an exponent 0<α<1. For the first two cases, where one of the parameters is fixed, nonrelativistic and relativistic waves present anomalous localization. However, for the latter case, in which both parameters follow a Lévy distribution, nonrelativistic and relativistic waves present a transition between anomalous and standard localization as the incidence energy increases relative to the barrier height. Moreover, we obtain the localization diagram delimiting anomalous and standard localization regimes, in terms of incidence angle and energy. Finally, we verify that transmission fluctuations, characterized by its standard deviation, are universal, independent of barrier architecture, wave equation type, incidence energy, and angle, further extending earlier studies on electronic localization. We believe that our predictions can be verified in graphene nanoribbons, where Dirac electrons are the main charge carriers.
This publication was done in collaboration with Jonas R.F. Lima and Anderson L. R. Barbosa, both at UFRPE, and we began it before the covid-19 pandemic hit the world! We are all glad to finally see it out there.
Graduate student José Roberto da Silva, defended his Doctoral dissertation on Wednesday (29.06.2022) at 10:00 am, in a virtual auditorium via google meet. The thesis, entitled “Electronic transport in quasiperiodic nanostructures”, employed advances computational techniques such as efficient implementations of Green’s function calculations to calculate the electronic conductance of periodic and quasiperiodic graphene nanoribbons in the presence of defects and other perturbations.
José Roberto has been a member of TNG since 2017. During the last 4+ years he authored one publication, and has enough results for another one. We are very proud of his development as a scientist and look forward to his continued success.
Graphene nanoribbons present remarkable electronic transport properties which can be tailored to specific applications. We consider a quasiperiodic modulation in the electronic hopping of metallic armchair and zigzag graphene nanoribbons, originating a Fibonacci superlattice with two possible hopping parameters. The electronic conductance for various Fibonacci generations is calculated via the recursive Green’s function method. We observe that a quasiperiodic hopping modulation opens a conductance gap at the Fermi level of armchair nanoribbons, leading to a strong electronic localization regime. The localization length initially increases with Fibonacci generation and saturates for high order generations. Considering an energy slightly above the Fermi level, we obtain similar results for the armchair nanoribbon, while the zigzag nanoribbon eventually enters the localization regime for high order Fibonacci generations. Our results demonstrate that a quasiperiodic hopping modulation is a viable way to control the electronic transport in graphene nanoribbons, widening its range of possible application in nanoelectronic devices.
This publication stems from José Roberto’s PhD dissertation at UFRN, which has been co-supervised by Anderson L. R. Barbosa at UFRPE.
Thermal management is becoming more relevant nowadays in ever decreasing-size electronic and optical devices generating more heat per unit volume, and in materials used in jet engines. We have witnessed many advances in the theories of thermal transport in the past decade: discovery of new excitations, a better understanding beyond the Fourier regime, description of highly anharmonic systems are but a few examples. We have lined-up a remarkable team of speakers, from physics, chemistry, material science and engineering from all over the world, taking advantage of the virtual meeting format imposed by the covid19 pandemic.
In this publication we present a simple heuristic method to obtain the relaxation time and the temperature dependence of the electrical conductivity in 2D semiconductors. The approach is computationally straightforward, and relies on the BoltzTraP algorithm, on a direct fitting procedure, and on a scaling at a reference temperature. The approach provides a good estimate for the thermoelectric figure of merit ZT. We demonstrate our approach in nitrogenated holey graphene (NHG), boron-doped NHG, and tungsten disulfide 2D-WS2. In all these cases, our results agree with computationally expensive calculations available in the literature at a fraction of the computing time.
This annual workshop series highlights advances in applications, algorithms, and parallel implementations of computer simulation methods for the study of condensed matter systems. It features topics such as Monte Carlo, molecular dynamics, and other numerical studies of material growth, structural and magnetic phase transitions, polymers, surfaces and interfaces, strongly correlated electron systems and exotic quantum phases, granular flow, diffusion, membranes and protein folding.
Encontro de Física do Norte e Nordeste (North and northeast physics meeting) promoted by the Brazilian Physical Society is the second largest Physics meeting in Brazil, gathering more than 500 researchers from the north and northeast regions of Brazil. In 2021, the event takes place online, hosted by Universidade Federal de Pernambuco, from 18 to 20 of October.