Specifically Southeast Nanjing's metamaterials group. Anything affiliated with them I scrutinize more. Which is not to say their work should be automatically dismissed, but diligence is required. The book Spy Schools has an entire chapter on one of their most infamous examples, which happened ~2006-2007-ish.

I’m in this field. This might have been novel a decade and a half ago. This particular research group also has a history of sending grad students/postdocs to U.S. universities to scoop ongoing research, crudely duplicate it in China, and publish it first (at a lower quality).