Pressure Induced Superconductivity; How it Relates to Structural Changes in Lithium Isotopes*

Superconductors are materials characterized by zero electrical resistance and perfect diamagnetism. As the third lightest element, lithium is the simplest of all known superconductors, and as such, can provide unique insights into superconductivity. Pressure induced superconductivity in lithium was shown by several groups (Deemyad et al., Shimizu et al., Struzhkin et al. 2002) and exhibits a very complicated behavior. Although the origin of this complex superconducting phase diagram was attributed to the structural properties of lithium, the structure of lithium within its superconducting region was not measured until now.    

In this study, we attempt to better characterize the structural changes within the superconducting region of lithium isotopes through analysis of synchrotron X-Ray Diffraction (XRD) data we obtained in Argonne National Laboratory. We establish the low temperature and high pressure phase boundaries of lithium between 0 and 55GPa.

In addition, we show that the transition from fcc structure to hR1 phase coincides with sudden drop in the superconducting transition and we show the boundaries of this phase in comparison with what has been previously thought. We further show that lithium does not exhibit isotope effects in its phase boundaries in this region. In this poster I will present the results of these studies and discuss the theoretical calculations of Tc values of the FCC-hR1-CI16 phases that can be directly compared to experimental data.