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Um pouco sobre nossa pesquisa no Jornal da USP.

Entrevistas/midia (in portuguese)

I am now in a sabattical period returning at the end of 2024 (Desember, 2024). Please, have this in mind if you plan to contact me for a project supervision (undergrad/master/PhD).

2022 - 2023  New papers !!!

• Electronic doping and correlations in Cr and Mn  substituted BaFe2As2

  High temperature superconductivity (HTSC) is observed in hole doped Iron-based superconductors (FeSCs), as in K-substituted BaFe2As2 (KBFA). HTSC, however, is not observed in putative hole doped Cr- and Mn- substituted BaFe2As2 (CrBFA and MnBFA, respectively). This naturally raises the questions as for why HTSC is not formed in CrBFA and MnBFA. In the FeSCs, magnetism and HTSC are intertwined phenomena. It is understood by some models that in the FeSCs the electronic structure close to the Fermi level is key to understand their magnetism and subsequently how HTSC is formed. In a pair of papers, we characterized the electronic structure of CrBFA and MnBFA for different compositions of Cr and Mn. We showed that Cr promotes hole doping in CrBFA whereas Mn barely dopes the parent compound. Instead, we showed that in MnBFA the bands acquire a large degree of incoherence (disorder). Moreover, in both cases, we found clear signatures of electronic correlations. We thus concluded that HTSC is not formed in these two materials due to the competition between the Fe and Cr (Mn) derived magnetism. More important, our work shows that the electronic structure close to the Fermi level has little impact on the CrBFA and MnBFA magnetic properties. This is strong evidence that the FeSCs are a new class of correlated metals, known as Hund’s metals.

          This is part of the PhD work of Marli, a former student in our group., now a postdoctoral researcher at the ESRF (France, Grenoble).   

           Marli R Cantarino, KR Pakuszewski, Björn Salzmann, Pedro HA Moya, Wagner R Silva Neto, GS Freitas, PG Pagliuso, C Adriano, Walber H Brito,  Fernando A Garcia, "Hole doping and electronic correlations in Cr-substituted BaFe2As2", arXiv:2312.09014, (2023).

          Marli R Cantarino, Kevin R Pakuszewski, Björn Salzmann, Pedro HA Moya, Wagner R da Silva Neto, Gabriel S Freitas, Pascoal G Pagliuso, Walber H Brito, Claude Monney, C Adriano, Fernando A Garcia, "Incoherent electronic band states in Mn-substituted BaFe2As2", Physical Review B, 108, 24, 245124 (2023).          

• Novel luminescent materials as sensors for critical infrastructure

         Layered double hydroxides (LDHs) are materials formed by the stacking of positively charged 2D networks (or layers) of edge-sharing octahedra of divalent and trivalent metal cations bridged by hydroxyl groups.  In a collaboration led by Prof. Danilo Mustafa, we have been working on how to resolve the microstructure of intercalated rare-earth cations that are added to the region in between the layers of the hydroxided. We discovered that the photoluminescence properties (PL) of Eu3+ hosted in the hydroxide layers of LDHs enables calibrationless quantification of anions in the interlayers.  The concept was demonstrated during the nitrate-to-carbonate ion exchange in Zn2+/Al3+/Eu3+ LDHs and can be implemented as a remote optical sensor to detect intrusion of anions such as Cl− or CO32−.  Our work has a direct application as a sensor allowing non-destructive remote detection of the progress of the carbonation front of critical concrete structures, such as bridges, dams, etc. 

          This is part of a collaboration led my Prof. Danilo Mustafa. 

          Alysson F Morais, Ivan GN Silva, Bruno J Ferreira, Alexandre C Teixeira, Sreeprasanth P Sree, Huayna Terraschke, Fernando A Garcia, Eric Breynaert, Danilo Mustafa, "Eu3+ doped ZnAl layered double hydroxides as calibrationless, fluorescent sensors for carbonate", Chemical Communications, 59, 91, 13571-13574 (2023).  

• Vibrational dynamics in filled skutterudites and a bridge between Physics an Chemistry

      There exists a family of materials called filled skutterudites. The vibrational and elastic properties of this family of materials are key parameters in the search for efficient thermoelectric materials. In this work, we investigated the RFe4Sb12 slutterudites, with R being Na, K, Ca, Sr, or Ba. Specifically, the interaction between the vibrations of R atoms (called the fillers) and the Fe4Sb12 atoms (called the cage) is a topic of continuous investigation. It is understood that the R fillers vibrations scatter the collective vibrations of the Fe4Sb12 cage structure, decreasing the overall thermal conductivity of the material. In turn, this leads to the increase of the thermoelectric figure of merit ZT, which states how good a thermoelectric material is. In this work, we performed x-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD)  experiments of the mentioned samples. We were able to characterize the role of the R atomm in the vibrational and elastic properties of the RFe4Sb12 materials. Moreover, our experimental results were connected with quantum chemistry calculations of the filler-cage bonding properties in skutterudites,  bridging physical and chemical  properties in this important family of materials.  

          This is part of the master work of Juliana Abrantes, a former student in our group.    

          Juliana G. de Abrantes, Marli R. Cantarino, Wagner R. da Silva Neto, Victória V. Freire, Alvaro G. Figueiredo, Tarsis M. Germano, Bassim Mounssef, Jr., Eduardo M. Bittar, Andreas Leithe-Jasper, and Fernando A. Garcia - “Vibrational and structural properties of the RFe4Sb12  ( R= Na, K ,Ca , Sr, Ba ) filled skutterudites”, Phys. Rev. Materials 6, 085403 (2022).

• Orbital localization and the role of the Fe 4p orbitals

         Roughly, solid materials may be metals, insulators or semiconductors. Metals are said to be good condutors, meaning that they can carry electricity with a minimun of electric resistance. Some metals, however,  display an extraordinary property that is the  ability to carry electricity without electrical resistance. This property is named superconductiviy and emerges at suffcient low temperatures. To understand superconductivity in a metal, it is key to understand its electronic structure, wich in the case of metals is usually understood in terms of the  so-called electronic bands. This type of knowledge is based upon concepts that are quite distinct from the better known properties of atomic orbitals that we all learn in chemistry. In the recently discovered Iron Based Superconductors (IBS), the electronic structure  present a dual character, which concerns the fact the  orbital character  of the electronic bands is strong. In the usual sense, the IBS electronic bands are believed to be dominated by the Fe 3d orbitals. Here, we show that the Fe and As 4p states also contribute to the electronic structure in a decisive way that should be taken into account to understand how the IBS electronic structure is tuned towards the superconducting properties. 

         This is part of the master work of Alvaro Figueiredo, a former student in our group. 

         A. G. de Figueiredo, M. R. Cantarino, W. R. da Silva Neto, K. R. Pakuszewski, R. Grossi, D. S. Christovam, J. C. Souza, M. M. Piva, G. S. Freitas, P. G. Pagliuso, C. Adriano, F. A. Garcia - "Orbital Localization and the Role of the Fe and As 4p Orbitals in BaFe2As2 Probed by XANES",  Physical Review B 105, 045130 (2022). 

Brief-CV

2023 - present - Postdoctoral researcher - Ames National Laboratory/Iowa State University, IA, United States.

2022 - present - Associate Professor - University of São Paulo, São Paulo, Brazil (on leave)

2014 -2022 - Assistant Professor - University of São Paulo, São Paulo, Brazil

2012 - 2014 - Post-doc researcher - UNICAMP, Campinas, Brazil

2011 - 2012 - Post-doc researcher - Max Plack Institute - CPFS,  Dresden, Germany

2007 - 2010 -  Doctor of Sciences - UNICAMP, Campinas, Brazil

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