The Physics department colloquia are usually on Friday afternoons at 3 pm in Room 135. Coffee and cookies are served at 2:45 pm in the same room. Anyone is welcome.

A Century of Superfluidity & the Evolution from BCS to BEC: from Mercury to Neutron Stars, from Nuclei to Ultra-cold Atoms
Prof. Carlos A. R. Sá de Melo, Dept. of Physics, Georgia Institute of Technology

Since the discovery of superconductivity at the laboratory of Kamerlingh Onnes in 1911, the phenomenon has become ubiquitous in Nature. Over the span of a century, innumerous charged superfluids (supercondutors) have been discovered with varying degrees of complexity from mercury to heavy fermions, from cuprates to the pnictides. The number of corresponding neutral superfluids, however, was kept at essentially two, until the mid-1990’s, when ultracold Bose atoms were cooled below micro-Kelvin temperatures, and the mid-2000’s, when ultracold Fermi atoms joined the new list of neutral superfluids. Neutral or charged superfluids are very interesting systems that have been found in metals, neutron stars, nuclei and ultra-cold atoms. For a given metal, neutron star, or nuclei there is essentially “zero” tunability of the particle density or interaction strength, and thus superfluid properties cannot be controlled at the turn of a knob. However, in ultra-cold Fermi atoms the interaction strength and the particle density can be tuned to change qualitatively and quantitatively superfluid properties. This tunability allows for the study of the evolution from BCS (weak coupling) superfluidity of large Cooper pairs to Bose-Einstein condensation (strong coupling) superfluidity of tightly bound molecules. I will discuss the BCS to BEC evolution in s-wave and p-wave angular momentum channels, and will conclude that this evolution is just a crossover phenomenon for s-wave, while a topological quantum phase transition takes place for the p-wave case.