To the OP:
I looked at your profile and from what I can tell, you have completed your PhD at a university in Brazil in the area of physics (or materials science) related to phase transitions.
Are you currently
(a) employed as a postdoc and seeking projects to work in complex systems,
or
(b) seeking postdoctoral positions outside of Brazil in complex systems?
If (b), then some places I can think of for opportunities include the following:
1. Santa Fe Institute (
www.santafe.edu) - research institute devoted to complex systems. Try and see if there are any postdoc opportunities available there.
2. Center for the Study of Complex Systems, University of Michigan (lsa.umich.edu/cscs). According to the website, they are seeking tenure track position there.
3. Complex Systems Society (
https://cssociety.org/job-openings) has a number of postings in EU countries for postdoc positions. Two of those positions are based in Spain -- I'm curious as a Brazilian citizen what your fluency would be in Spanish (I've been told that Portuguese speakers have little trouble picking up Spanish).