Abstract
We present a relativistic effective field theory for the interaction between acoustic and gapped phonons in the limit of a small gap. We show that, while the former are the Goldstone modes associated with the spontaneous breaking of spacetime symmetries, the latter are pseudo-Goldstones associated with some (small) explicit breaking. We hence dub them "pseudo-acoustic" phonons. In this first investigation, we build our effective theory for the cases of one and two spatial dimensions, two atomic species, and assuming large distance isotropy. As an illustrative example, we show how the theory can be applied to compute the total lifetime of both acoustic and pseudo-acoustic phonons. This construction can find applications that range from the physics of bilayer graphene to sub-GeV dark matter detectors.
Highlights
Many properties of solids are dictated by the dynamics of their simplest collective excitations: the phonons
While the former are the Goldstone modes associated with the spontaneous breaking of spacetime symmetries, the latter are pseudo-Goldstones associated with some explicit breaking
In this work we presented a relativistic effective field theory for the description of the low-energy degrees of freedom of a solid made of two species, weakly coupled to each other
Summary
Many properties of solids are dictated by the dynamics of their simplest collective excitations: the phonons. As we will show, we expect a small gap for the pseudoacoustic phonons to arise when the different species are weakly coupled to each other Such an instance is realized, for example, in few-layer materials such as graphene [6,31,32,33,34,35,36,37], hexagonal boron nitride [38,39], or a combination of the two [40]. In constructing the EFT for acoustic and pseudoacoustic phonons we impose relativistic Lorentz invariance This might not be common in solid-state physics, there are reasons why this approach is worth exploring. The EFT of pseudoacoustic phonons could find application in “solid” theories of inflation; see [3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
