Emily Townsend’s thesis research

My thesis research is in the area of theoretical solid state physics. I used finite temperature Green’s functions (which are a neat trick for doing quantum mechanics and statistical dynamics) to calculate (predict) the behavior of the effective mass of electrons in a heavy-fermion superconductor.

An effective mass is a way of parameterizing the interactions that electrons have with each other and the rest of the stuff in a solid. If the interactions make the electrons hard to move, we say they have a higher effective mass. Heavy fermion materials have huge electron effective masses—up to 1000 times a bare electron’s mass—due to quantum mechanical hybridization and correlations. Some of these materials can become superconducting at very low temperatures (~ 4 Kelvin). This means that the electrons pair up, which allows them to occupy a single quantum state. In this state, among other important characteristics, they can all move together without the loss of energy. This means that superconductors can carry an electric current (moving electric charges) without resistance (the energy loss by heat which is normally seen when a current runs through a wire).

I am trying to understand why the effective mass of the electrons in heavy fermion materials becomes much smaller when the materials are cooled down and transition into the superconducting state. One possibility is that this is a general feature of superconductors, but it may also be a characteristic limited only to the heavy fermion materials.