Critical behaviour of cubic n = d-component spin systems

Yoshitake Yamazaki, Moyuru Ochiai, Yoshiichi Fukuda +1 more

Z Usatenko, Józef Spałek

The critical behaviour at the ordinary transition in semi-infinite n -component anisotropic cubic models is investigated by applying the field theoretic approach in d = 3 dimensions up to the two-loop approximation. Numerical estimates of the resulting two-loop series expansions for the critical exponents of the ordinary transition are computed by means of Padé resummation techniques. For n < n c the system belongs to the universality class of the isotropic n -component model, while for n > n c the cubic fixed point becomes stable, where n c < 3 is the marginal spin dimensionality of the cubic model. The obtained results indicate that the surface critical behaviour of the semi-infinite systems with cubic anisotropy is characterized by a new set of surface critical exponents for n > n c .

Subir Sachdev A

Thomas Nattermann, Steffen Trimper

The influence of the cubic anisotropy both in the quadratic and quartic part of an n-component 'spin' Hamiltonian is examined in the framework of a parquet-graph summation. For values of the anisotropy parameter f larger than a critical value, f - , a first-order transition occurs which corresponds to the appearance of complex fixed points in the renormalization group approach. On the other hand for f<f - a first- or second-order transition occurs depending on f, n and the values of the bare coupling constants. For second-order transitions a quantity m(n,f) plays the role of an effective number of components, m(n,0)=n. For m>4 and m<-8 the system has a strongly cubic behaviour whereas 0<m<4 a weakly cubic behaviour is observed; the latter changes to pure isotropic behaviour for f to 0. For -8<m<0 the behaviour is strongly or weakly cubic depending on the values of the bare coupling constants.

春彦 松尾

Yuan Chen, Zhibing Li

The renormalization group approach is applied to the study of the short-time critical behaviour of the d -dimensional n -component anisotropic cubic spin systems with long-range interaction of the form p σ s p s - p in momentum space. Firstly, the system is quenched from a high temperature to the critical temperature and then relaxes to equilibrium within the model A dynamics. The asymptotic scaling laws and the initial slip exponents θ' and θ of the order parameter and the response function, respectively, are calculated to the second order in = 2σ- d . For 1⩽ d <2σ and n > n c , the cubic anisotropy affects the short-time critical behaviour.