Periodic Reporting for period 1 - TopoPress (Tuning Topological Materials by hydrostatic Pressure and uniaxial Stress)
Periodo di rendicontazione: 2022-02-01 al 2024-01-31
The main issue focused in this fellowship is related to the current electronic devices, such as tablets, cell phones and computers, efficiency. Inside these devices, there are two types of electrons (which are small particles): the free electrons and the localized electrons. The localized electrons hold small pieces of information (spin) and create a memory for the current devices, in this way images and files can be stored. On the other hand, the free electrons are responsible for powering the devices by carrying around small packages of energy (charge) and changing the information stored in the localized ones. Both types of electrons interact with each other, either by colliding or just by feeling the presence of the other. These interactions are called correlations and are an important property for the efficiency of the devices. Another useful property is the path that the free electrons choose to carry information or energy. Some paths result in fast and organized movement of electrons while others can be slower and more complicated, wasting power. The shape of the paths or surfaces chosen can be associated to topology. The interplay between correlations and topology is not yet fully understood and is a promising area for the development of new and more efficient electronic devices. Therefore, in this project we have studied materials to enhance the knowledge on the edge of these two fundamental areas: strong correlations and topology. These studies are of great importance to the society as they are fundamental to the creation of better and more efficient electronic devices. Therefore, the research performed presented a great importance for the development of innovations and for creating/enabling clean and sustainable energy for the society, which fits in the UN sustainable development goals.
The main objectives of this research were to perform electrical resistivity experiments under hydrostatic compression or uniaxial strain in strongly correlated electron systems. These experiments are similar to what happens inside a pressure cooker or when we use a rubber band. By mechanically compressing things in all directions (pressure cooker) or in one direction (rubber band), we can change the properties of materials. For example, in the pressure cooker, the water boils at a higher temperature, so the food cooks faster. In the rubber band, when we pull, the band gets thinner or thicker. But instead of preparing a dish faster or holding things together we aimed to change the properties of materials by compressing in all directions (hydrostatic pressure) or by pushing and pulling in one direction (uniaxial strain).
The main objectives of this research were to perform electrical resistivity experiments under hydrostatic compression or uniaxial strain in strongly correlated electron systems. These experiments are similar to what happens inside a pressure cooker or when we use a rubber band. By mechanically compressing things in all directions (pressure cooker) or in one direction (rubber band), we can change the properties of materials. For example, in the pressure cooker, the water boils at a higher temperature, so the food cooks faster. In the rubber band, when we pull, the band gets thinner or thicker. But instead of preparing a dish faster or holding things together we aimed to change the properties of materials by compressing in all directions (hydrostatic pressure) or by pushing and pulling in one direction (uniaxial strain).
We have investigated several promising materials, such as CeAlGe, CeSbTe, CeAlSi, MoTe2 and HfTe5 by performing electrical resistivity experiments under hydrostatic pressure and/or uniaxial strain. Instead of pressure cookers and rubbers we use devices that can mechanically compress materials, called pressure cells. Our samples were crystals similar to table salt, so to perform the experiments, the crystals were cut and polished into nice bars. They were then loaded into the pressure cells with electrical wires attached to them to measure electrical resistance. The main results of this research are the creation of a model to explain the properties of CeAlSi, which can be extended to other materials. This research has also provided important insights into the superconductivity present in the topological material MoTe2.
In total seven promising topological and strongly correlated materials were investigated during this fellowship contributing significantly to the state of the art in this field. The impact of the results obtained can be assessed by the number of four papers already published and many are in preparation. Therefore, the tasks performed during this fellowship have led to high-quality results and have expanded the knowledge at the interface of two important fields of physics: condensed matter and topology, which are fundamental for the development of new technologies to provide society with clean and sustainable energy.