Permaculture (short for "permanent agriculture" but also expanded to be short for "permanent culture") is a set of ethics, principles, and actions. The philosophy is based on 3 ethics:
Bill Mollison coined the term permaculture:
"Permaculture...is the conscious design and maintenance of agriculturally productive which have the diversity, stability, and resilience of natural ecosystems. It is the harmonious integration of landscape and people providing their food, energy, shelter, and other material and non-material needs in a sustainable way. Without permanent agriculture there is no possibility of a stable social order. Permaculture design is a system of assembling conceptual, material, and strategic components in a pattern which functions to benefit life in all its forms. The philosophy behind permaculture is one of working with, rather than against, nature; of protracted and thoughtful observation rather than protracted and thoughtless action; of looking at systems in all their functions, rather than asking only one yield of them; and of allowing systems to demonstrate their own evolutions." p. ix, in Mollison, B. (1990). Permaculture: A practical guide for a sustainable future. Washington, DC: Island Press.
Permaculture is an incredibly interdisciplinary topic. It can be addressed as a set of principles and ethics; a movement; and as a practice in lifestyle, healthcare, agriculture, etc. Therefore, it can be researched as a scientific topic but also as a social science topic. Searching interdisciplinary databases is your best bet for finding scholarly articles. Google Scholar is a great place to start; make sure to look at the journal titles and authors and think about searching within those publications and for those authors in other databases and the library catalog. In order to set up your Google Scholar settings, see the tab on Searching Google Scholar: Basics. Think about what aspect of permaculture you are interested in and brainstorm keywords to use in searching both databases and the library catalog.
Sustainable land use
Sustainable food systems
Make sure to check out this guide that will lead you to specific resources on Organic Gardening/Sustainable Agriculture.