Speaker
Description
The amplitude mode is a fundamental phenomenon that emerges from a broken continuous symmetry. In the framework of Ginzburg-Landau theory, this corresponds to an oscillation of the complex order parameter $\Delta$, which characterizes the long-range order of superfluids and superconductors. Typically, this mode is unstable and decays rapidly into pair-breaking excitations that exist within a continuum. Therefore, its experimental detection in strongly interacting systems has historically been challenging, and theoretical efforts have proposed mechanisms to suppress coupling to these pair-breaking excitations [1].
In my poster I will show that an ultracold quasi-2D Fermi gas exhibits a long-lived amplitude mode in the strongly interacting regime. We excite the amplitude mode via trapping modulation spectroscopy, thereby influencing the interaction energy. These measurements show a narrow resonance at $2 \Delta$, suggesting a long lifetime. We support these results by direct measurement of the coherent oscillations of the momentum distribution.
Additionally, the spectral response features an avoided crossing between the pairing gap energy $2 \Delta$ and the second excited state of the trapping potential. The experimental evidence combined with a two-band superconductor model, suggests that the admixture of this excited state provides a route to stabilize the amplitude mode, effectively pushing it out from the pair-breaking continuum.
[1] D. Pekker, C. Varma, Annu. Rev. Condens. Matter Phys.6,269–297 (2015).
