  Nanoscale electromechanical coupling provides a unique route towards control
of mechanical motions and microwave fields in superconducting cavity
electromechanical devices. Though their successes in utilizing the
optomechanical or electromechanical back-action effects for various purposes,
aluminum imposes severe constraints on their operating conditions with its low
superconducting critical temperature (1.2 K) and magnetic field (0.01 T). To
extend the potential of the devices, here we fabricate a superconducting
electromechanical device employing niobium and demonstrate a set of cavity
electromechanical dynamics including back-action cooling and amplification, and
electromechanically induced reflection at 4.2 K and in strong magnetic fields
up to 0.8 T. This device could be used to realize electromechanical microwave
components for quantum technologies by integrating amplifiers, converters, and
circulators on a single chip that can be installed at the 4K stage of dilution
refrigerators. Moreover, with its ability to control and readout nanomechanical
motions simultaneously, this niobium electromechanical transducer could provide
powerful nanomechanical sensing platforms.
