Pseudomagnetic fields for sound at the nanoscale

14.06.2017, 11:32

Unlike electrons, phonons do not feel a magnetic field, since they are not charged. As a consequence, much of the interesting physics connected to the behaviour of charged particles in a magnetic field is absent for phonons, be it the Lorentz force or the uni-directional transport along the edges of the sample. In the past two years, researchers have started to study how one might make sound waves behave in ways similar to electrons in a magnetic field or related "topological" settings. On the macroscopic scale, progress has been rapid, even with first experimental implementations involving coupled pendula or gyroscopes or exploiting air currents. However, such ideas cannot be directly translated into nanophysics. In this manuscript, we describe a novel design that is well suited for the nanoscale. It is purely geometric in nature and could be implemented based on an already experimentally demonstrated platform, a simple patterned 2D material.

 

Our design takes inspiration from graphene. In a strained graphene sheet, electrons feel so-called "pseudo-magnetic fields". These are like real magnetic fields, except that electrons near each of the two "Dirac" points in graphene's bandstructure feel a different sign of the field. We show how something analogous can be generated in a so-called "snowflake" phononic crystal, which is well-known in optomechanics, making it attractive in terms of optical excitation and read-out.

 

Our results pave the way towards helical transport of sound waves on the nanoscale, enabling phononic networks and fundamental studies into heat transport.

Contact: christian.brendel(at)mpl.mpg(dot)de

Group: Marquardt Division

Reference: C. Brendel et al. PNAS 2017