Huge Symmetric Elastoresistance in the Kondo Lattice YbRh 2 Si 2

Heavy-fermion metals are prototype correlated electron systems for the study of Kondo entanglement and quantum criticality. We use the symmetry decomposed elastoresistance to uncover the fingerprints of strain-dependent Kondo scattering as function of temperature and magnetic field in the prototypical tetragonal Kondo lattice YbRh$_2$Si$_2$. By combining longitudinal and transverse resistance measurements under uniaxial strain applied along the tetragonal $[100]$ and $[110]$ directions, we obtain the elastoresistive responses in the in plane $A_{1g}$, $B_{1g}$, and $B_{2g}$ symmetry channels. While the responses in the symmetry-breaking channels are negligible, a huge enhancement of the isotropic symmetric $A_{1g}$ elastoresistance is found approaching -50 at low temperatures. Scaling analysis and comparison with linear thermal expansion measurements reveal that the symmetric elastoresistance probes the contribution of Kondo scattering to the strain dependence of magnetic entropy and signals strain- and field controlled quantum criticality upon cooling to 2 K.