To search for critical works on Sylvia Plath, try a keyword search:
sylvia plath criticism
or a subject search using this format:
Plath, Sylvia -- Criticism and interpretation
MLA is the best place to search for articles and book chapters on any topic related to literary criticism. With MLA you do not need to add the search term "criticism". Try a simple keyword search, for example:
sylvia plath and ariel
retrieves critical articles on Plath's poem "Ariel". If full text is not available through MLA, use the SCLinks button to locate other sources of the article.
Other sources to try: