  The use of current-generated spin-orbit torques[1] to drive magnetization
dynamics is under investigation to enable a new generation of non-volatile,
low-power magnetic memory. Previous research has focused on spin-orbit torques
generated by heavy metals[2-8], interfaces with strong Rashba
interactions[9,10] and topological insulators [11-14]. These families of
materials can all be well-described using models with noninteracting-electron
bandstructures. Here, we show that electronic interactions within a strongly
correlated heavy fermion material, the Kondo lattice system YbAl$_{3}$, can
provide a large enhancement in spin-orbit torque. The spin-torque conductivity
increases by approximately a factor of 4 as a function of decreasing
temperature from room temperature to the coherence temperature of YbAl$_{3}$
($T^* \approx 37$ K), with a saturation at lower temperatures, achieving a
maximum value greater than any heavy metal element. This temperature dependence
mimics the increase and saturation at $T^*$ of the density of states at the
Fermi level arising from the ytterbium 4$f$-derived heavy bands in the Kondo
regime, as measured by angle-resolved photoemission spectroscopy[15]. We
therefore identify the many-body Kondo resonance as the source of the large
enhancement of spin-orbit torque in YbAl$_{3}$. Our observation reveals new
opportunities in spin-orbit torque manipulation of magnetic memories by
engineering quantum many-body states.
