Sunam Co. tumbled as much as -21%, extending Tuesday’s -30% slide.

South Korean stocks that had skyrocketed on perceived links to superconductors fell for a second day Wednesday after a US university research center rebutted recent claims of a breakthrough in the technology.

Sunam Co. dropped as much as -21%, extending its -30% slide Tuesday after the post from the University of Maryland’s Condensed Matter Theory Center. Duksung Co. and Mobiis Co. similarly declined for a second day.

The stocks had surged since Korean researchers last month said they had created the world’s first superconductor able to conduct electricity at room temperature and ambient pressure, using a material called LK-99. The long-sought technology promises to revolutionize industries from computing to power, if it actually works.

While the post from the University of Maryland’s Condensed Matter Theory Center threw cold water on the recent stock frenzy, the head of the institute left the door open to disagreement.

“Could I be wrong? Of course, anyone can be wrong,” Dr. Sankar Das Sarma, director of the center, said in an email to Bloomberg News. “I do not think that the subject ends today even if LK-99 has no SC,” he said, “but I will be paying no attention to the topic any longer.”

Meanwhile, the Korean Society of Superconductivity and Cryogenics said it is proceeding as planned with its own validation process on the claims.