In this talk, after an introduction to thermoelectric (TE) properties, we analyze recently synthesized graphene nanoribbon (GNR) heterostructures that are obtained as extensions of pristine  armchair graphene nanoribbons (AGNRs). After simulating their band structure through a nearest-neighbor tight-binding model, we use the Landauer formalism to calculate the necessary TE coefficients, with which we obtain the electrical conductance G, thermopower S, thermal conductance Ke, and figure of merit ZT (using literature results for the phonon thermal conductance Kph), at room temperature. We then compare the results for the nanoribbon heterostructures with those for the pristine AGNR nanoribbons. The comparison shows that the metallic AGNRs become semiconducting (with much higher ZT values) after the inclusion of the extensions that transform them into heterostructures and that some heterostructures have higher values of ZT when compared to the semiconducting pristine AGNRs from which they  have originated.

In this talk, we will present some recent results on the quantum transport of electrons through quantum dots and quantum rings coupled to normal and topological superconductors. In addition, we will discuss the effects of Andreev reflections and Majorana zero modes on the transport and electronic properties of the systems.

[1] Medina, Fabian; Martinez, Dunkan; Diaz-Fernandez, Alvaro; Dominguez-Adame, Francisco;  Rosales, Luis; Orellana, Pedro A.  SCIENTIFIC REPORTS 12 1071 2022
[2] Gonzalez, IA ; Pacheco, M; Calle, AM; Siqueira, EC ; Orellana, PA  SCIENTIFIC REPORTS 11 3941 2022

This talk is divided in two parts. In the first part, I´ll briefly describe the Brazilian Nanotechnology National Laboratory (LNNano), an open facility for research and innovation in the field of nanoscience and nanotechnology located in Campinas, Brazil, in the same campus as three other National Laboratories which include Sirius, a 4th generation synchrotron facility. In the second part, I´ll discuss our recent joint theory/experiment work on the formation and rupture of monatomic ZrO2 wires.

A bound state in the continuum (BIC) is a discrete energy level within the continuous portion of a spectrum. BICs have been identified in optical systems, and the findings have led to  advances in telecommunication technology. Less productive has been the search in nanostructured devices. The subject of this talk, a system belonging to the latter class, has attracted some attention in the last two decades. The device comprises a quantum wire coupled to two identical quantum dots and is modelled by a two-impurity Anderson model with a single conduction channel. The symmetry with respect to dot exchange splits the spectrum of the model Hamiltonian into even and odd sectors; the dot orbitals form a bonding (even) level and an antibonding (odd) level. While the antibonding orbital constitutes a BIC in the noninteracting model, the Coulomb interaction hybridizes it with odd eigenstates in the continuum. This hybridization accurately accounted for, a numerical renormalization-group computation of the spectral density for the antibonding orbital will be shown to pinpoint a virtual BIC in the low-energy spectrum. The BIC is virtual because the Anderson catastrophe forbids transitions to the lowest level in the even sector of the spectrum. Particle-hole excitations allow transitions to  higher even states and broaden the spectral density asymmetrically into a divergent power-law akin to an x-ray edge singularity. This smearing can nonetheless be avoided: additional numerical results will be presented to show that adequate tuning of a gate potential avoids the catastrophe, washes out the contribution  from particle-hole excitations, and recovers the infinitely sharp line distinctive of a BIC.

Two-dimensional systems (2D) are a 'pure surface', and its properties can be adjusted by modulating its environment. For instance, depositing a 2D system over different substrates, stacking them in heterostructures, adding a twist angle between different layers, or depositing molecules 
onto it. In this talk, we will discuss all these examples through nano-Raman spectroscopy. Such environmental perturbations cause phonon and electron localization at a nanometer scale; the consequences and effects of such perturbations on the 2D systems are then understood through their atomic modelling. 

A metal can be driven to an insulating phase through distinct mechanisms. A possible way is via the Coulomb interaction, which then defines the Mott metal-insulator transition (MIT). Another possibility is the MIT driven by disorder, the so-called Anderson MIT. In this talk I will discuss the use of quantum entanglement to identify and characterize the MIT in disordered Hubbard chains with interacting fermions — thus comprising the Mott-Anderson physics [1,2]. 

[1] Phys. Rev. B 104, 134201 (2021).
[2] arXiv: 2202.01557 (2022). 

Polymers are complex molecules having a reach set of topologies that affect their diffusive behavior.  Understanding how polymers diffusive has been a topic of great scientific and applied interest on a variety of fields.  As an example, a theoretical model of a polymer can as a paradigm to other long molecules, such as those commonly found in biology.

Recent research interest has shifted from bulk studies, where there is more complete understanding to studies on surfaces. I will present some recent work based of polymer diffusion on more realistic cases, including preliminary results for bioapplications.

We consider the dynamics of a measured SYK model. The latter can be viewed as a universal many-body Hamiltonian for mesoscopic sized quantum systems. Focusing on the observable of state purification, we analytically describe the limits of strong and weak measurement rate, where in the latter case monitoring up to time scales exponentially long in the numbers of particles is required. We complement the analysis of the limiting regimes with the construction of an effective replica theory providing information on the stability and the symmetries of the respective phases. The analytical results are tested by comparison to exact numerical simulations.

Symmetry-enforced nodal-line semimetals are immune to perturbations that preserve the underlying symmetries. This fundamental robustness enables  investigations of fundamental phenomena and applications utilizing diverse  materials-design techniques. The drawback of symmetry-enforced nodal-line  semimetals is that the crossings of energy bands are constrained to symmetry- invariant momenta in the Brillouin zone. On the other end lies accidental nodal-line semimetals whose band crossings, not being enforced by symmetry,  are easily  destroyed by perturbations. Some accidental nodal-line semimetals have, however, the advantage that their band crossings can occur in generic  locations in the Brillouin zone, and thus can be repositioned to tailor material properties. We show that lattice engineering with periodic distributions of vacancies yields a hybrid type of nodal-line semimetals which possess symmetry-enforced nodal lines and accidental nodal lines, with the latter endowed with an enhanced robustness to perturbations. Both types of nodal lines are explained by a symmetry analysis of an effective model which captures the relevant characteristics of the proposed materials and are verified by first-principles calculations of vacancy-engineered borophene and graphene polymorphs. Our findings offer an alternative path to relying on complicated compounds to design robust nodal line semimetals; one can instead remove atoms from a common monoatomic material.

The interplay between electronic interactions and disorder poses one of the most difficult problems in condensed matter systems. One-dimensional systems provide one of the few cases where reliable descriptions can be obtained. This is possible by means of a powerful Renormalization Group method developed towards the end of the 20th century. In this talk, I hope to describe the central ideas behind this method and to show some recent results. I will highlight some generic properties that can hopefully be useful in higher dimensions.