China has started scrutinizing more carefully its exports of indium, an element that is key to making high-speed chips for AI data centers, raising concerns that export curbs could follow as Beijing has done with other critical minerals. Indium, a silvery-white metal named for its indigo blue line in the atomic spectrum, is not on any of China’s export control lists. But several buyers and customers have flagged to Reuters that they have recently faced increased checks and scrutiny by the Chinese Customs over their purchases of the metal.…