In 2015, Mikhail Eremets, a physicist at the Max Planck Institute for Chemistry in Mainz, Germany, reported that hydrogen sulfide — a molecule consisting of two hydrogen atoms and one sulfur atom — turned superconducting at minus 94 degrees Fahrenheit when squeezed to about 22 million pounds per square inch. That was a record warm temperature for a superconductor at the time.
“That’s, I would say, the game-changing paper that sort of set the tone,” Dr. Dias said.
Dr. Eremets and other scientists subsequently discovered that lanthanum hydride — a compound containing hydrogen and lanthanum — reached a superconducting temperature of minus 10 degrees Fahrenheit at ultrahigh pressures.
Dr. Dias’s group looked at a mixture of three elements: hydrogen, sulfur and carbon. With three elements, the scientists were able to adjust the electronic properties to achieve the higher superconducting temperatures.
“You can start with knowing what the good binary systems are and then potentially adding another element to it to get more complex,” said Eva Zurek, a professor of chemistry at the University at Buffalo who performs numerical calculations to predict the behavior of the high-pressure materials. “And hopefully, this complexity can bring the superconducting critical temperature up or stabilization pressure down.”
Dr. Zurek, who was not involved with the latest research, said carbon was a good third element to add because it formed strong bonds that could potentially keep the material together. “If you release the pressure, then those bonds potentially will not break,” she said.
To make the superconductor, the scientists had to squeeze the substance between two diamonds to nearly 40 million pounds per square inch. That is approximately the pressure you’d experience if you could tunnel more than 3,000 miles into the Earth and arrived at the bottom of the molten iron outer core.
The process produced specks of material about the volume of a single inkjet particle.
The experimental results did not fully agree with Dr. Zurek’s computer calculations, which predicted the highest superconducting temperatures at lower pressures. Dr. Dias instead found that the superconducting temperature continued to increase as the pressure rose.