Vibrational Dynamics and Superconductivity in Intermetallic Cage Systems
Intermetallic cage systems are a broad class of compounds whose crystal structure can be rationalized in terms of a host framework (the cage) inside which one may find a guest, or filler, element. A subject of central importance in this field is achieving an understanding of how the guest vibrational dynamics changes the total vibrational dynamics of the system, and how it can interfere with the many physical properties depending upon it.
In this seminar, I intend to approach this subject by presenting recent experiments on some skutterudite compounds. Skutterudites are a particular type of intermetallic cage systems which have the general formula RT4X12. The R elements, here the guests, reside in the large void space in the framework of the [T4X12] host structure. Skutterudites have been investigated in the last years and were shown to present physical properties ranging from exotic strongly correlated ground states as well as a good potential for applications as thermoelectric materials.
The relative flexibility of the host structure to the inclusion of distinct guest ions, opens the possibility of a large size mismatch between guest and host (oversized cages). In turn, this favors a significant change in the vibrational state of the R ions affecting the total vibrational states of the system. By a judicious choice of these elements, one may tune the total vibrational dynamics of the system, tailoring targeted physical properties. Such procedure may play a fundamental role, for instance, in the electron-phonon coupling of these compounds, which is of fundamental importance in the formation of the superconducting state.