Seminar
Tuesday, 20 September, 2011
Group Seminar LMU: Topological phase transitions in ultra-cold Fermi superfluids: The evolution from BCS to BEC under artificial spin-orbit fields (Double feature)
Tuesday, 20.09.2011 14:00 p.m. (s.t.) in H107, Fakultät für Physik LMU
Prof. Carlos A. R. Sa de Melo, Georgia Institute of Technology
Topological quantum phase transitions in superfluids with non-s-wave order parameters have been conjectured theoretically in the context of p-wave [1] and d-wave [2] systems for many years, but never observed experimentally due to the absence of tunable parameters. In this talk, I discuss topological phase transitions in ultra-cold Fermi superfluids induced by interactions and artificial spin orbit fields, which are tunable parameters in the context of ultra-cold atom physics. I construct the phase diagram for population imbalanced systems at zero and finite temperatures, and analyze spectroscopic and thermodynamic properties to characterize various phase transitions. For balanced systems, the evolution from BCS to BEC superfluids in the presence of spin-orbit effects is only a crossover as the system remains fully gapped [3], even though a triplet component of the order parameter emerges. However, for imbalanced populations, spin orbit fields induce a triplet component in the order parameter that produces nodes in the quasiparticle excitation spectrum leading to bulk topological phase transitions of the Lifshitz type [4]. Additionally a fully gapped phase exists, where a crossover from indirect to direct gap occurs, but a topological transition to a gapped phase possessing Majorana fermions edge states does not occur.
[1] G. E. Volovik, Exotic Properties of Superfluid 3He, World Scientific, Singapore (1992).
[2] R. D. Duncan and C. A. R. Sa de Melo, Phys. Rev. B 62, 9675 (2000).
[3] Li Han, C. A. R. Sa de Melo, arXiv:1106.3613v1.
[4] Kangjun Seo, Li Han and C. A. R. Sa de Melo, arXiv:1108.4068v2.