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

Using Monte Carlo simulations including the lattice degree of freedom [1], for the first time the nematic susceptibility of the spin fermion model for the pnictides is calculated [2]. The results are in very good agreement with experiments by J-H. Chu et al., Science 337, 710 (2012). Our study suggests a nematicity in the spin fermion model primarily originating on magnetism, but with the lattice/orbital also playing an important role by 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 a characteristic temperature $T^*$ being the $T_N$ of the purely electronic system. In this regime, a pseudogap in the density of states and short-range magnetic order is observed. \\[4pt] [1] S. Liang et al., PRL 111, 047004 (2013)\\[0pt] [2] S. Liang et al., arXiv:1405.6395 (2014), to appear in PRB.