  Thanks to the recent discovery on the magic-angle bilayer graphene,
twistronics is quickly becom11 ing a burgeoning field in condensed matter
physics. This letter expands the realm of twistronics to acoustics by
introducing twisted bilayer phononic graphene, which remarkably also harbors
the magic angle, evidenced by the associated ultra-flat bands. Beyond mimicking
quantum mechanical behaviors of twisted bilayer graphene, we show that their
acoustic counterpart offers a considerably more straightforward and robust way
to alter the interlayer hopping strength, enabling us to unlock magic angles (>
3 degrees) inaccessible in classical twisted bilayer graphene. This study, not
only establishes the acoustical analog of twisted (magic-angle) bilayer
graphene, providing a testbed more easily accessible to probe the interaction
and misalignment between stacked 2D materials, but also points out the
direction to a new phononic crystal design paradigm that could benefit
applications such as enhanced acoustic emission and sensing.
