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| Author(s): |
Kevin Raduenz Pakuszewski
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2017-12-13 |
| Examining board members: |
Cris Adriano;
Francisco Rouxinol;
Fernando Assis Garcia
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| Advisor: | Cris Adriano; Pascoal José Giglio Pagliuso |
| Abstract | |
In this work one presents Angle Resolved Photoemission Spectroscopy (ARPES) studies on the distinct families of Ce2RhIn8 and Ba(Eu)Fe2As2, that have its properties governed by the collective behavior of the interacting electrons. In these compounds, the electronic and magnetic properties are inter related giving interesting phenomena, such as non-conventional superconductivity. Therefore, ARPES is a suitable technique that allows the study of the band structure of a solid, helping one to unravel the behavior of the interacting electrons close to the Fermi level. Ce2RhIn8 is a heavy fermion compound that belongs to the family of CemMIn3m+2 (M = Rh, Ir, Co and m = 1, 2), known to host a lot of heavy fermion superconductors. This compound presents a tetragonal bilayer crystal structure and is a paramagnetic metal at room temperature, but undergoes to an antiferromagnetic phase below TN = 2.8K. The heavy fermions compounds are known to present a diversity of physical phenomena, as unconventional superconductive, magnetic ordering, non-Fermi liquid behavior and the occurrence of quantum critical point. The manifestation of each one of these phenomena depend of an intricate equilibrium between several interactions that act on the system, e. g., Kondo effect, RKKY magnetic interactions and crystal field effect. For the family CemMIn3m+2, due the occurrence of Kondo effect, the theory predicts that several compounds from this family should to manifest in it band structure the emergence of a hybridization gap in the conduction bands, together with the arising of a flat band in EF due the hybridization between 4f electrons and conduction electrons. Therefore, one of the objectives during this master degree was to study the formation of this flat band in Ce2RhIn8 compound by means of on-resonance ARPES, a variation of ARPES technique, which enable us to enhance the photoemission from 4f orbital and measure this band. The Fe-based superconductors, EuFe2As2 and BaFe2As2 present a tetragonal crystal structure at room temperature and undergo to an orthorhombic structure in a temperature TS. They are paramagnetic metal at room temperature and presents a spin density wave (SDW) phase below TSDW. For the FeAs-based compounds, their density of states near EF is almost universal, mainly populated by electrons from 3d level of iron. The Fe 3d level has five orbitals, where we have three-fold degenerate t2g states (dxy, dxz and dyz) and two-fold degenerate eg states (dz2 and dx2-y2). The contribution of each orbital to the Fermi Surface usually change considerably from compound to compound, which lead to a diversity of physical phenomena at low temperature, e. g., SDW antiferromagnetism and unconventional superconductive. As the Fermi surface is responsible for many of the electrical and magnetic proprieties in the solids, determining the orbital contribution of each band that form the Fermi surface is essential to have a correct understand about the physics behind these compounds, in particular, the arising of superconductivity. Therefore, one of the motivations to study the EuFe2As2 and BaFe2As2 by means of ARPES technique was the idea to obtain the orbital contribution of each band that form the Fermi surface in these compounds and compare our result with other macroscopic proprieties of them in the literature. Actually, many studies suggest that the predominance of planar/bidimensional orbitals (dxy/dx2-dy2) at the Fermi surface favors the arising of superconductivity in this class of materials. Thus, the ARPES technique is a very powerful tool to probe directly the band structure of the material and thereby obtain the orbital character of each band near the Fermi surface. As we will see later, ARPES is a spectroscopy technique that use photons to excite electrons from solids, where the intensity of photoemission is extremely dependent of the experimental geometry, in such way that only some orbitals from Fe 3d level can be detected in a fixed geometry (AU) | |
| FAPESP's process: | 15/18544-2 - Investigation of Electronic Structure of Heavy Fermions compounds studied by Angle-resolved Photoemission Spectroscopy |
| Grantee: | Kevin Raduenz Pakuszewski |
| Support Opportunities: | Scholarships in Brazil - Master |