Materials informatics is a new field of research that uses tools from data science to design, discover and understand new materials. In Brazil, CNPq has recently approved an INCT on this subject, focusing on several different areas of condensed matter physics, materials chemistry and materials science. In this talk I will discuss the recent advances in this area and present two works focusing on the magnetic properties and also on spin splittings in 2D compounds.

The volume of data generated in the world has increased exponentially, and in the last 10 years,
it is no longer possible to store all the data generated. In 2020, about 40 trillion gigabytes of
data were generated. But, after all, what does it matter in the academic world? What does this
impact on the business of a small, medium or large company? How can this impact our life?
The answer starts with the search for people with technical training to work in the processing of
all this volume of data. They are professionals with the ability to translate information into
strategic decisions, essential within companies, in research and innovation. At this moment, we
are faced with a major problem: there are not enough people in the world with enough technical
skills, today and in the next 10 years, to work in the areas of data and generate value with them.
Why such an intense search for professionals who work with data?
Companies have already understood that the data driven culture generates an increase in
revenue, cost reduction and improvement in people's quality of life.
And when we say “companies” we mean all market segments: industry, health, retail, finance,
e-commerce, wholesale, among others.
There are almost 20 million companies in Brazil alone. Imagine 1% of them hiring technology
professionals, we are talking about 2 thousand vacancies, but we already know that the
projection is 700 thousand vacancies from today to the next 5 years.
With the information mentioned, the question remains about how the academic area,
universities, faculties, technical institutes and schools can be structured to technically train all
this volume of people. In addition, how to generate a greater bond between educational
institutions and companies so that this process can be accelerated and optimized for people
who intend to enter the job market.
The idea of this seminar is to present how big data and analytics are being implemented in real
cases in companies from different sectors. How Data Science, Data Engineering, Machine
Learning Engineering, DevSecOps Engineering MLOps, DataOps and Cloud Architecture are
being structured.
 

Two-dimensional heterostructures with nanometer scale unit cells realized via moiré and nanopatterned engineering provide tunable platforms to observe electronic Hofstadter bands in lattices pierced by magnetic flux per unit cell comparable to the flux quantum h/e. The celebrated fractal spectrum and the topological properties of the single particle states have long been associated with quantum Hall phenomena. In this talk, I will theoretically discuss new states of matter that result when Hofstadter electrons form Cooper pairs. I will begin by providing a general symmetry-based classification of such Hofstadter superconductors that highlights the role of magnetic translation symmetries in determining the irreducible representations of such paired states [1]. This classification shows that Hofstadter superconductors are described by multi-component charge 2e order parameter supporting rich phase diagram, and that pairing implies breaking of magnetic translation symmetries.  

Second, I will employ a renormalization group (RG) analysis on the square lattice Hofstadter-Hubbard model to demonstrate that the combination of repulsive interactions with the presence of a tunable manifold of Van Hove singularities provides a new mechanism for driving unconventional superconductivity in Hofstadter bands [2]. Specifically, the number of Van Hove singularities at the Fermi energy can be controlled by varying the flux per unit cell and the electronic filling, leading to instabilities toward nodal superconductivity and chiral topological superconductivity with Chern number C = ±6. The latter is characterized by a self-similar fixed trajectory of the RG flow and an emerging self-similarity symmetry of the order parameter. This analysis uncovers new potentialities for the realization of unconventional symmetry broken and topological orders in Hofstadter quantum materials.

[1] Theory of Hofstadter Superconductors, D. Shaffer, J. Wang and L.H. Santos, Phys. Rev. B 104, 184501 (2021)

[2] Unconventional Self-Similar Hofstadter Superconductivity from Repulsive Interactions, D. Shaffer, J. Wang and L.H. Santos, arXiv:2204.13116  

The use of medicinal drugs represented a great evolution for humanity regarding disease combat. As a consequence, human life expectancy in the last century has increased considerably. However, there are still several issues to be addressed in this area, mostly related to the physicochemical properties of bioactive agents and their side effects. For instance, despite the high amount of money and time spent yearly by the pharmaceutical industry in drug research, several active pharmaceutical ingredients are launched in the market still presenting low aqueous solubility, low thermal stability, low tabletability, frequent incidence of annoying side effects, among others. Therefore, approaches that could contribute to overpass such issues are of great importance. Following these lines, this talk will present two approaches that might be helpful in this regard: encapsulation of drug molecules within the interlamellar space of clay minerals and the cocrystallization of active pharmaceutical ingredients with generally recognized as safe materials. Through some examples from recent studies, it will be shown that, in fact, cocrystallization and encapsulation in clay minerals stand as promising alternatives to enhance the effectiveness of active pharmaceutical ingredients end minimize their side effects.

As an atomically thin membrane, graphene is a highly flexible material, a property that provides the opportunity to use strain engineering to control its electronic properties. Wrinkled or rippled graphene, suspended or on a substrate, reveals inhomogeneous charge distributions originating from underlying strain fields. Scanning tunneling microscopy (STM) measurements on locally deformed samples demonstrated electron confinement with peculiar charge distributions that break sublattice symmetry. The phenomena that differentiate carbon atoms in each unit cell result in local valley currents with application in the field of valleytronics, i.e., the manipulation of the valley degree of freedom for electronic purposes. Our previous studies demonstrated that valley filtering properties highly depend on the type of deformation considered, suggesting the possibility of producing them by design. Motivated by these ideas, we analyzed the fate of charge distributions in models of graphene with several Gaussian-shaped out-of-plane deformations arranged in different geometries. These preliminary works revealed the emergence of moiré-like patterns with pockets of localized charges and naturally led us to consider periodic (global) arrays of deformations. These systems describe various experimental settings where graphene lies on top of specially designed substrates with arrays of deformations. Strains induced by such structures result in superlattice potentials that modify electron dynamics and become practical tools to engineer the band structure. By considering different strain configurations, we identify the conditions for the existence of flat bands in the electronic band structure that present maximal band-gap separation. The origin of these bands is traced back to the unique nature of electronic states that separate into ‘trivial’ isolated bound states and ‘percolating topological’ states. These two types of states coexist in different spatial regions with distinct lattice geometries and give rise to unique signatures when measured by local probes such as STM. Under applied external voltages, transport may occur via topological chiral states in bands with non-trivial Chern numbers that percolate through the sample.

Recent results in strongly correlated electronic systems will be discussed. Employing computational techniques, I will address several surprising states that emerge in coupling regions with competing tendencies. Specifically, I will first focus on low-dimensional chains and ladders, where the density matrix renormalization group technique is an accurate tool. The computer reveals a variety of exotic phases difficult to anticipate, such as spin arrangements of ferromagnetic blocks [1], as well as spirals without any obvious source of frustration [2]. Predictions for inelastic neutron scattering for block states will be presented [3]. Coupling the spirals to a canonical s-wave superconductor induces in the spiral both singlet and triplet pairing and, thus, Majorana states at the edges [4]. I will also discuss the adiabatic movement of Majoranas, first step towards braiding, employing time-dependent methods. Spirals-like arrangements, but now in two dimensions, can also originate when including spin-orbit coupling and a magnetic field, creating a regularly spaced array of skyrmions, called “skyrmion crystal” [6]. This crystal can also be a platform for Majoranas [7]. Finally, time allowing, I will discuss progress with regards to pairing in multi-orbital models, employing a two-orbital Hubbard version of the Haldane chains [8], as well as low dimensional versions of models for iron superconductors [9]. 

Work supported by the US Department of Energy (DOE), Office  of  Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division.

[1] See for example N. Patel et al, Commun. Phys. 2, 64 (2019); 
M. Sroda, E. Dagotto, and J. Herbrych, PRB 104, 045128 (2021), and references 
therein. 
[2] J. Herbrych et al, Proc. Natl. Acad. Sci. USA 117, 16226 (2020).
[3] J. Herbrych et al., Nat. Comm. 9, 3736 (2018); J. Herbrych et al. PRB 
102, 115134 (2020).
[4] J. Herbrych et al, Nat. Comm. 12, 2955 (2021).
[5] B. Pandey et al., submitted for publication.
[6] N. Mohanta et al., Phys. Rev. B 100, 064429 (2019) (Editor’s choice). 
See also N. Mohanta et al., Commun. Phys. (Nature) 3, 229 (2020).
[7] N. Mohanta et al., Commun. Phys. (Nature) 4, 163 (2021). 
[8] N. D. Patel et al., npj Quantum Mater. 5, 27 (2020).
[9] B. Pandey et al., PRB 103, 214513 (2021) and references therein.

The sp, sp2, and sp3 carbon hybridizations allow an almost infinite number of different structures with tunable mechanical and electronic properties. These structures can exhibit different topologies with different electronic dimensions (0-fullerenes,1-nanotubes, 2-graphene, 3-diamond). These topologies can be exploited to create a large class of different materials, such as bucky papers [1], carbon nanotube-based artificial muscles [2,3], foams [4], auxetic crystals [5], etc. These materials present extremely complex morphologies, which results in a difficult challenge to realistically model their mechanical and structural properties. In this talk, we will present and discuss multi-scale (from fully atomistic to macroscale) approaches to model these materials, including the use of artificial intelligence methods (such as the bioinspired ANT algorithms). Of particular interest are the new molecular dynamics simulation techniques based on reactive potentials that allow handling multi-million atom systems. These techniques can be also used for non-carbon materials, such as chalcogenides [6] and other non-van der Waals solids [7].

[1] L. J. Hall, V. R. Coluci, D. S. Galvao, M. E. Kozlov, M. Zhang, S.
O.Dantas, and R. H. Baughman, Science v320, 5875 (2008).
[2] M. D. Lima et al., Science v338, 6109 (2012).
[3] Z. F. Liu et al., Science v349, 400 (2015),
[4] R. Wang et al., Science v366, 216 (2019).
[5] R. H. Baughman and D. S. Galvao, Nature v375, 735 (1993).
[6] S. Lei et al., Nature Nanotech. v11, 465 (2016)
[7] A. P. Balan et al., Nature Nanotech. v13, 602 (2018).

Trans-Neptunian Objects (TNOs) are those that orbit the Sun from a distance further than Neptune's orbit. Due to their distance, they suffer less space weathering, thus remaining with their physical characteristics for a longer time. Because of this, they are considered Solar System fossils. Using the Stellar Occultation technique, an astronomical event that happens when a Solar System Body passes in front of a star, we are able to determine some of the object's characteristics. The most interesting characteristics we are able to find is the presence of rings, atmosphere, binarity, or the presence of satellite. In my work, I have contributed to developing and improving the method of analysis of stellar occultations. Furthermore, I'm involved in projects to observe stellar occultations by space telescopes, like the James Webb and CHEOPS.
 

In most materials, electrons fill bands, starting from the lowest kinetic energy states. The Fermi level is the boundary between filled states below and empty states above. This is the basis for our very successful understanding of how metals and semiconductors work. But what if all the electrons within a band had the same kinetic energy (this situation is called a "flat band")? Then electrons could arrange themselves so as to minimize their Coulomb repulsion, giving rise to a wide variety of possible states including superconductors and magnets. Until recently, flat bands were achieved only by applying large magnetic fields perpendicular to a 2D electron system; in this context they are known as Landau levels. Fractional quantum hall effects result from Coulomb-driven electron arrangement within a Landau level. Eva Andrei and coworkers at Rutgers demonstrated flat minibands in graphene-based superlattices (two or more atomically-thin layers stacked on top of each other, with a twist angle between them.) More recently, Pablo Jarillo-Herrero of MIT and coworkers  discovered correlated insulators and superconductors at different fillings of these minibands. Remarkably, the band structure in these systems can be in principle rather well predicted and thus designed, as shown by Allan MacDonald and other theorists, backed up in practice by many experiments. Yet I will share two vignettes about how my group aimed for a particular behavior and found something quite different. The first led to the discovery of the first experimentally-known "orbital magnet", a ferromagnet in which the magnetic moments that align with each other are not spins but tiny circulating current loops. The second was observation of extremely strong (300X) magnetoresistance and other strange electronic properties over a broad range of electron filling -- this one took years to figure out, but we've recently explained it. Each of these two surprises turned out to be caused by an aspect of the layer structure which had not previously been considered important. Finally, I'll reflect on what might enable us to get more repeatable control of structure and thus electronic properties in such twisted systems.