The key to this discovery was creation of a metallic, hydrogen-rich compound at very high pressures: roughly 2 million atmospheres. The researchers used diamond anvil cells, devices used to create high pressures, to squeeze together miniscule samples of lanthanum and hydrogen. They then heated the samples and observed major changes in structure. This resulted in a new structure, LaH10, which the researchers previously predicted would be a superconductor at high temperatures.
While keeping the sample at high pressures, the team observed reproducible change in electrical properties. They measured significant drops in resistivity when the sample cooled below 260 K (minus 13 C, or 8 F) at 180-200 gigapascals of pressure, presenting evidence of superconductivity at near-room temperature. In subsequent experiments, the researchers saw the transition occurring at even higher temperatures, up to 280 K. Throughout the experiments, the researchers also used X-ray diffraction to observe the same phenomenon. This was done through a synchrotron beamline of the Advanced Photon Source at Argonne National Laboratory in Argonne, Illinois.
“We believe this is the beginning of a new era of superconductivity,” Russell Hemley, a research professor at the GW School of Engineering and Applied Science, said. “We have examined just one chemical system – the rare earth La plus hydrogen. There are additional structures in this system, but more significantly, there are many other hydrogen-rich materials like these with different chemical compositions to explore. We are confident many other hydrides—or superhydrides—will be found with even higher transition temperatures under pressure.”
Recent predictions and experimental observations of high
superconductivity in hydrogen-rich materials at very high pressures are driving the search for superconductivity in the vicinity of room temperature. We have developed a novel preparation technique that is optimally suited for megabar pressure syntheses of superhydrides using modulated laser heating while maintaining the integrity of sample-probe contacts for electrical transport measurements to 200 GPa. We detail the synthesis and characterization of lanthanum superhydride samples, including four-probe electrical transport measurements that display significant drops in resistivity on cooling up to 260 K and 180–200 GPa, and resistivity transitions at both lower and higher temperatures in other experiments. Additional current-voltage measurements, critical current estimates, and low-temperature x-ray diffraction are also obtained. We suggest that the transitions represent signatures of superconductivity to near room temperature in phases of lanthanum superhydride, in good agreement with density functional structure search and BCS theory calculations.
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