Piezoelectrically Tuned Multimode Cavity Search for Axion Dark Matter
  The $\mu$eV axion is a well-motivated extension to the standard model. The
Axion Dark Matter eXperiment (ADMX) collaboration seeks to discover this
particle by looking for the resonant conversion of dark-matter axions to
microwave photons in a strong magnetic field. In this Letter, we report results
from a pathfinder experiment, the ADMX "Sidecar," which is designed to pave the
way for future, higher mass, searches. This testbed experiment lives inside of
and operates in tandem with the main ADMX experiment. The Sidecar experiment
excludes masses in three widely spaced frequency ranges (4202-4249, 5086-5799,
and 7173-7203 MHz). In addition, Sidecar demonstrates the successful use of a
piezoelectric actuator for cavity tuning. Finally, this publication is the
first to report data measured using both the TM$_{010}$ and TM$_{020}$ modes.
