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Peeking into a diamond pressure cell
A defining characteristic of a superconductor is that it expels an external magnetic field. Demonstrating this effect can be tricky when the sample is under enormous pressures in a diamond anvil cell. Troyan et al. placed a tinfoil sensor inside a sample of H2S under pressure. They then bombarded it with synchrotron radiation and watched how the scattering of photons of tin nuclei changed over time. When H2S was in the normal state, an external magnetic field reached the sensor through the sample, causing the nuclear levels of tin to split. In the superconducting state, however, no splitting was observed because H2S expelled the field before it could reach the sensor.
Science, this issue p. 1303
Abstract
High-temperature superconductivity remains a focus of experimental and theoretical research. Hydrogen sulfide (H2S) has been reported to be superconducting at high pressures and with a high transition temperature. We report on the direct observation of the expulsion of the magnetic field in H2S compressed to 153 gigapascals. A thin 119Sn film placed inside the H2S sample was used as a sensor of the magnetic field. The magnetic field on the 119Sn sensor was monitored by nuclear resonance scattering of synchrotron radiation. Our results demonstrate that an external static magnetic field of about 0.7 tesla is expelled from the volume of 119Sn foil as a result of the shielding by the H2S sample at temperatures between 4.7 K and approximately 140 K, revealing a superconducting state of H2S.
