New effective-field theory with correlations; application to disordered magnets

Raf Dekeyser, G. Kamieniarz

T. Kaneyoshi

D. Bitko

C. Svoboda, D. Nozadze, Fawaz Y. Hrahsheh +1 more

We investigate the influence of spatial disorder correlations on smeared phase transitions, taking the magnetic quantum phase transition in an itinerant magnet as an example. We find that even short-range correlations can have a dramatic effect and qualitatively change the behavior of observable quantities compared to the uncorrelated case. This is in marked contrast to conventional critical points, at which short-range correlated disorder and uncorrelated disorder lead to the same critical behavior. We develop an optimal fluctuation theory of the quantum phase transition in the presence of correlated disorder, and we illustrate the results by computer simulations. As an experimental application, we discuss the ferromagnetic quantum phase transition in Sr 1− x Ca x RuO 3 .

C. Broholm, G. Aeppli

Mustansir Barma

It is pointed out that the spin-spin correlation function in a magnetic-polymer model is proportional to the generating function of the probability function describing the spatial distribution of monomers. This observation is used to generalize Thorpe's study of a freely jointed magnetic polymer, to take the excluded-volume effect into account using a scaling theory. The inverse magnetic correlation length measured along the polymer plays the role of a scaling field which can, therefore, be controlled experimentally. However, strong disorder in the magnetic coupling can prevent this field from reaching its critical value, zero.