Tuning the electronic structure of FeSe superconductors with applied strain

Since their discovery in 2006, iron-based superconductors have attracted much of the interest of the scientific community and have been the object of intense studies using state-of-the-art techniques. Strain measurements represent a modern technique which may play an important role in unveiling new electronic features and understanding high temperature superconductivity. This thesis presents experimental results obtained by investigating the electronic behaviour of a FeSe single crystal under uniaxial applied strain. In the first chapters, I will be presenting the basic characteristics of iron-based superconductors and recent experimental studies under strain on other superconductors. Then, I will introduce the apparatus and the experimental methods used to collect the experimental data. I performed a series of transport measurements of a single crystal FeSe across a large temperature regime without and with uniaxial applied strain. My results indicate that FeSe under applied uniaxial strain shows three different temperature regimes. Firstly, at high temperature the resistivity increases with increasing strain, followed by an opposite variation of the resistivity slope under strain below 70 K in the nematic state. At low temperature, the slope is again positive and no strain variation is seen at a unique temperature, which resembles the critical temperature of superconductivity. This study found the superconducting state is enhanced under compressive strain and suppressed under tensile strain. This experiment is one of the first studies conducted on FeSe single crystal under uniaxial strain. Further studies are needed to reproduce the observed measurements.