  Microwave detectors based on the spin-transfer torque diode effect are among
the key emerging spintronic devices. By utilizing the spin of electrons in
addition to charge, they have the potential to overcome the theoretical
performance limits of their semiconductor (Schottky) counterparts, which cannot
operate at low input power. Here, we demonstrate nanoscale microwave detectors
exhibiting record-high detection sensitivity of 75400 mV mW$^{-1}$ at room
temperature, without any external bias fields, for input microwave power down
to 10 nW. This sensitivity is 20x and 6x larger than state-of-the-art Schottky
diode detectors (3800 mV mW$^{-1}$) and existing spintronic diodes with >1000
Oe magnetic bias (12000 mV mW$^{-1}$), respectively. Micromagnetic simulations
supported by microwave emission measurements reveal the essential role of the
injection locking to achieve this sensitivity performance. The results enable
dramatic improvements in the design of low input power microwave detectors,
with wide-ranging applications in telecommunications, radars, and smart
networks.
