  Plasmonic nanolasers have ultrahigh lasing thresholds, especially those
devices for which all three dimensions are truly subwavelength. Because of a
momentum mismatch between the propagating light and localized optical field of
the subwavelength nanocavity, poor optical pumping efficiency is another
important reason for the ultrahigh threshold but is normally always ignored.
Based on a cavity-embedded nanoantenna array design, we demonstrate a
room-temperature low-threshold plasmonic nanolaser that is robust,
reproducible, and easy-to-fabricate using chemical-template lithography. The
mode volume of the device is~0.22({\lambda}/2n)3 (here,{\lambda} is resonant
wavelength and n is the refractive index), and the experimental lasing
threshold produced is ~2.70MW/mm2. The lasing polarization and the function of
nanoantenna array are investigated in detail. Our work provides a new strategy
to achieve room-temperature low-threshold plasmonic nanolasers of interest in
applications to biological sensoring and information technology.
