Raman scattering experiments on LaFeAsO with splitted antiferromagnetic (TAF M = 140 K) and tetragonal-orthorhombic (TS = 155 K) transitions show a quasi-elastic peak (QEP) in B2g symmetry (2 Fe tetragonal cell) that fades away below ∼ TAF M and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the T −dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. The large separation between TS and TAF M in LaFeAsO compared with their coincidence in BaFe2As2 manifests itself in slower dynamics of nematic fluctuations in the former. The discovery of Fe-based superconductors (FeSCs) with high transition temperatures (above 100 K in FeSe films [1]) triggered much interest on these materials [2][3][4][5]. Nematicity, characterized by large in-plane electronic transport anisotropy [6], is normally observed below a tetragonal-orthorhombic transition temperature T S , and seems to be also present in other high-T c superconductors [7]. Also, divergent nematic susceptibility in the optimal doping regime suggests that nematic fluctuations play an important role in the superconducting pairing mechanism [8]. Thus, investigations of the nematic order and fluctuations in FeSCs and their parent materials are pivotal to unraveling the origin of high-T c superconductivity. Clearly, it is necessary to identify the primary order parameter associated with the nematic phase [4, 5]. A relation between nematicity and magnetism is suggested by the near coincidence between T S and the antiferromagnetic (AFM) ordering temperature T AF M in some materials, most notably BaFe 2 As 2 with T AF M ∼ T S = 138 K [9,10]. In fact, the magnetic ground state is a stripe AFM phase that breaks the 4-fold tetragonal symmetry of the lattice (see Fig. 1(a)), providing a natural mechanism for electronic anisotropy. On the other hand, T S and T AF M are significantly separated for LaFeAsO (LFAO) (T AF M = 140 K and T S = 155 K) [11][12][13], while FeSe does not order magnetically at ambient pressure but still shows a nematic transition at T S = 90 K [14], motivating suggestions that the nematic transition may be driven by charge/orbital degrees of freedom rather than magnetism in the latter [16,17]. However, even for FeSe the magnetic scenario may still apply [18]. In * Present address: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.Ba(Fe 1−x Co x ) 2 As 2 and other doped systems, the splitting between T AF M and T S increases with doping [9,15]. Overall, the primary order parameter that drives the structural/nematic transition at T S and the dominating mechanism of T AF M /T S separation in parent FeSCs are not fully settled yet.Raman scattering was recently employed as a probe of nematic fluctuations in FeSCs and their parent materials. In A(Fe 1−x Co x ) 2 As 2 (A = Ca, Sr, Ba, Eu) [1, 4,19,21,22,24,25], Ba 1−p K p Fe 2 As 2 [25], FeSe [26,27] and NaFe 1−x Co x As [28], a quasi-elastic ...

In this paper we revisited the Ziff-Gulari-Barshad model to study its phase transitions and critical exponents through time-dependent Monte Carlo simulations. We use a method proposed recently to locate the nonequilibrium second-order phase transitions and that has been successfully used in systems with defined Hamiltonians and with absorbing states. This method, which is based on optimization of the coefficient of determination of the order parameter, was able to characterize the continuous phase transition of the model, as well as its upper spinodal point, a pseudocritical point located near the discontinuous phase transition. The static critical exponents β, ν_{∥}, and ν_{⊥}, as well as the dynamic critical exponents θ and z for the continuous transition point, were also estimated and are in excellent agreement with results found in literature.