Critical Adsorption in Systems with Weak Surface Field: The   Renormalization-Group Approach
  We study the surface critical behavior of semi-infinite systems belonging to the bulk universality class of the Ising model. Special attention is paid to the local behavior of experimentally relevant quantities such as the order parameter and the correlation function in the crossover regimes between different surface universality classes, where the surface field h_1 and the temperature enhancement can induce additional macroscopic length scales. Starting from the field-theoretical phi^4 model and employing renormalization-group improved perturbation theory (epsilon expansion), explicit results for the local behavior of the correlation and structure function (0-loop) and the order parameter (1-loop) are derived. Supplementing earlier studies that focussed on the special transition, we here pay particular attention to the situation where a large c suppresses the tendency to order in the surface (ordinary transition) but a surface field $h_1$ generates a small surface magnetization m_1. Our results are in good agreement with recent phenomenological considerations and Monte Carlo studies devoted to similar questions and, combined with the latter, provide a much more detailed understanding of the local properties of systems with weak surface fields. 
A. Ciach and U. Ritschel