The dream of transmitting electricity without energy loss has driven decades of superconductivity research. Some of the most promising candidates yet are superhydrides, hydrogen-rich materials that, under immense pressures, have exhibited superconducting behavior at temperatures far higher than conventional superconductors.
Now, an international team including scientists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has achieved a key breakthrough in studying these materials, using nuclear magnetic resonance (NMR) spectroscopy to probe lanthanum superhydrides under extreme pressure for the first time.
Superconductors are materials that lose all electrical resistance below a critical temperature specific to each material. This allows electricity to move through them without energy loss. In most known superconductors, that transition happens below about 140 Kelvin (minus 133 degrees Celsius), meaning practical use requires demanding cooling systems. Because of this, scientists are searching for materials that can become superconducting at much higher temperatures.
Superhydrides are hydrogen-rich compounds in which a metal, such as lanthanum, sits inside a tightly packed hydrogen lattice. Under enormous pressure, similar to conditions found inside planets, these materials can develop unusual electronic properties and may show superconductivity close to room temperature. They currently hold the world record for the highest critical transition temperature at which signs of superconductivity have been observed.
To reach those conditions, researchers compress the samples in diamond anvil cells, squeezing them between two diamonds at pressures greater than one million atmospheres. The difficulty is that the samples are extremely small, so studying them demands exceptional experimental precision.
The new work addresses that challenge with so-called Lenz lenses, tiny conductive ring structures that focus the high-frequency fields needed for nuclear magnetic resonance (NMR) spectroscopy directly into the sample volume. By concentrating and amplifying those fields, the lenses make NMR measurements possible under the extreme conditions inside a diamond anvil cell.
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