Investigation of emergent quantum phenomena in systems with reduced size and dimensionality

Abstract

The thesis project of the PhD candidate, Cauê Kaufmann Ribeiro would deal with a current puzzle in Condensed Matter Physics: the understanding of the underlying physics accounts for a Quantum Phase Transition (QPT) and emergent novel quantum phenomena. In order to overcome this challenge, we propose to investigate two selected strongly correlated electron systems under non-canonical tuning control parameters, i.e., the reduction of the system's dimensionality and volume size to the nanoscopic scale. The materials to be investigated are timely selected because of its predicted exotic quantum states close to a putative QPT: FeGa$_{3-y}$Ge$_{y}$ ($y$ = 0, 0.15 and 0.4) and FeSe$_{x}$Te$_{1-x}$ ($ x=$ 0, 0.5, 0.1). For the former FeGa$_{3-y}$Ge$_{y}$ our main goal is to investigate how the volume size and dimensionality reduction of the system influences the putative ferromagnetic (FM) Quantum Critical Point (FM-QCP) and the formation of collective spin supercurrents and hydrodynamic flow of phonons. The latters can bring a new arena for the investigation of spintronic andthermoelectricity, respectively. On the other hand, for the system FeSe$_{x}$Te$_{1-x}$ we plan to investigate the coexistence and/or competition between local magnetic moments and superconductivity close to a QPT as well as to give experimental evidences for the existence of protected topological superconductor states on the surface.In order to reach our goals, we will synthesize nanoparticles (using high-energy ball milling method) and thin films (using rf-sputtering and Molecular Beam Epitaxy-MBE) of these materials and measure their bulk and microscopic physical properties. While for the bulk properties, we commit to set new experimental methods in the IFUSP, for the microscopicproperties we are proposing a new methodology addresing Mössbauer spectroscopy (existing in IFUSP) to uncover protected topological surface states on thin film. Other physical property measurements will be performed in the laboratories of our (in-house and international) collaborators of this proposal together with a support coming from theoreticians to interpret our experimental finding. We expect that the results of this PhD thesis will contribute enormously with still open questions in the area of quantum matter and pave an alternative route to reach new generation of functional quantum materials with promising application in energy harvesting and quantum computing. In addition, we are willing that the DD1 candidate becomes an outstanding Doctor in Physics with hard skills on sample preparation, development of experimental methods beyond the state-of-the-art and problem solver of hot issues at the frontier of science. (AU)