Dartmouth Events

Abstract: Every mean-field superconductor has a complex order parameter, giving rise to two collective modes corresponding to amplitude (“Schmid-Higgs”) and phase (“Anderson-Bogoliubov-Goldstone”) fluctuations. Superconductors with additional structure can host a richer variety of collective modes, in the form of fluctuations which explore the larger order-parameter configuration space. Examples include Leggett modes (given multiple bands), Bardasis-Schrieffer modes (given one or more subdominant pairing channels), and clapping modes (given a multicomponent pairing channel). Crystal symmetries often impose selection rules which keep these modes dark in linear optical response. In this talk, I will outline a general effective-action approach to the theory of superconducting collective modes and describe how explicit or spontaneous symmetry breaking can optically activate them. I will show how emerging two-dimensional superconductors offer a promising platform for the study of exotic collective excitations, with special attention to rhombohedral graphene multilayers, where gate-tunable out-of-plane displacement fields or valley polarization can provide the requisite symmetry breaking.

Hosted By: Assistant Professor Rufus Boyack 

Zoom Link: https://dartmouth.zoom.us/j/99960465228?