  Understanding the nature of the electronic nematic phase in iron pnictide
superconductors is important for elucidating its impact on high-temperature
superconductivity. Here we use transport and inelastic neutron scattering to
study spin excitations and in-plane resistivity anisotropy in uniaxial pressure
detwinned BaFe$_2$As$_2$ and SrFe$_2$As$_2$, the parent compounds of iron
pnictide superconductors. While BaFe$_2$As$_2$ exhibits weakly first order
tetragonal-to-orthorhombic structural and antiferromagnetic (AF) phase
transitions below $T_s > T_N\approx 138$ K, SrFe$_2$As$_2$ has strongly coupled
first order structural and AF transitions below $T_s= T_N\approx 210$ K. We
find that the direct signatures of the nematic phase persist to lower
temperatures above the phase transition in the case of SrFe$_2$As$_2$ compared
to BaFe$_2$As$_2$. Our findings support the conclusion that the strongly
first-order nature of the magnetic transition in SrFe$_2$As$_2$ weakens the
nematic phase and resistivity anisotropy in the system.

Superconductivity;Strongly Correlated Electrons