Diverging Nematic Susceptibility, Physical Meaning of T* scale, and Pseudogap in the Spin Fermion Model for Pnictides

Using Monte Carlo simulations with a tunable uniaxial strain, for the first time the nematic susceptibility of a model for the pnictides is calculated. The results are in good agreement with the experiments by J-H. Chu {\it et al.}, Science {\bf 337}, 710 (2012). Via a Ginzburg-Landau analysis, our study suggests a nematicity in pnictides primarily originating on magnetism, but with the lattice/orbital boosting up critical temperatures and separating the structural $T_S$ and N'eel $T_N$ transitions. At $T>T_S$, Curie-Weiss behavior is observed with the characteristic temperature $T^{\ast }$ unveiled by Chu {\it et al.} being the $T_N$ of the purely electronic system. In this temperature regime, short-range magnetic order with wavevectors $(\pi ,0)-(0,\pi )$ induce local nematic fluctuations and a density-of-states pseudogap, compatible with several experiments.