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| Author(s): |
Jean Carlo Souza
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2022-04-12 |
| Examining board members: |
Pascoal José Giglio Pagliuso;
Iakov Veniaminovitch Kopelevitch;
Ricardo Donizeth dos Reis;
Mucio Amado Continentino;
Andrea Bianchi
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| Advisor: | Pascoal José Giglio Pagliuso |
| Abstract | |
The prediction and the subsequent experimental observation of new topological states of matter have created a whole new paradigm in condensed matter physics. Although a highly explored area, it is still controversial which fingerprints topology will leave in three dimensional systems. In this thesis, we grew single crystalline samples of a plethora of putative topological systems and studied them by means of transport, specific heat, magnetic, electron spin resonance and scanning tunneling microscopy/spectroscopy experiments. Our aim was to explore different techniques to complement the most traditional ones in the search of fingerprints of topological systems. Two different branches were explored to find those fingerprints. The first one is to look into the crystalline electrical field (CEF) effects, obtained through the magnetic properties of the systems. In this part, we first explored the half-Heuslers Y(Pd,Pt)Bi. We were able to verify experimentally, through scanning tunneling microscopy/spectroscopy, the proposed inversion between conduction and valence bands from the Pd compound to the Pt one. The second system explored was the proposed magnetic Weyl semimetals RAlX (R = La, Ce, Pr; X = Si, Ge). We were able to synthesize them by Al-flux grown and study the evolution from the CEF effects going from Si to Ge. We only observed any changes in the CEF effects for the Ce-based systems, which points out that the increase of hybridization is a key component for any changes in the CEF effects in those compounds. We show that the hybridization in Ce-based systems appears to play a much bigger role than previously thought. The second explored branch was to explore microscopically the relaxation of our probe in electron spin resonance (ESR). Particularly, we explored the Kondo insulator SmB6 and the nonsymmorphic antiferromagnet Eu5In2Sb6. For the SmB6 crystals, we made a minute substitution of Sm by Gd and showed that the Gd3+ ions act as a Kondo hole in this Kondo lattice. In the highly dilute regime, with a Gd3+ concentration of 200 parts per million, we were able to observe a clear signature of a relaxation through spin polarized surface states, which we explored with different tuning parameters. For the Eu5In2Sb6 systems, exotic quasiparticles known as magnetic polarons had a clear signature in the Eu2+ spin dynamics. We were also able to study in more details the intricate interplay of magnetic interactions in this system. Our thesis shows the possibility of finding topological fingerprints in the relaxation of our probe, which is reflected in the line shape and/or in the spin-spin relaxation, and in the crystalline electrical field effects due to the band inversion and/or hybridization of local moments. It opens a new route of exploring alternative techniques as smoking guns in the study of topological states of matter (AU) | |
| FAPESP's process: | 18/11364-7 - Magnetic properties of complex systems with non-trivial topology |
| Grantee: | Jean Carlo Souza |
| Support Opportunities: | Scholarships in Brazil - Doctorate |