This corresponds to half of the pressure of Earth’s core. With their high-pressure experiments the Mainz researchers have thus not only set a new record for superconductivity, their findings have also highlighted a potential new way to transport current at room temperature with no loss.
For many solid-state physicists, superconductors that are suitable for use at room temperature are still a dream. Special copper oxide ceramics, so-called cuprates, took the leading positions in terms of transition temperature, i.e., the temperature at which the material loses its resistance. The record for a ceramic of this type is roughly -140C at normal air pressure -109C at high pressure. In the ceramics, a special, unconventional form of superconductivity occurs. For conventional superconductivity, temperatures of at least -234C have so far been necessary.
METHOD: They used a pressure chamber <1 cubic centimeter in size. The 2 diamond tips on the side, which act as anvils, are able to constantly increase the pressure that the sample is subjected to. The cell is equipped with contacts to measure the electrical resistance of the sample. In another high-pressure cell, they observed magnetic properties of a material that also change at the transition temperature. After filling the pressure chamber with liquid hydrogen sulfide, they increased the pressure up to 2 megabar and changed the temp for each pressure level. They took measurements of both resistance and magnetization to determine the material’s transition temperature. Note that superconductor possesses ideal diamagnetic properties. They conducted magnetic high-pressure analyses to measure the Meissner effect.
MOA: They believe it is mainly H atoms that are responsible for H2S losing its electrical resistance under high pressure at relatively high temperatures: Hydrogen atoms oscillate in the lattice with the highest frequency of all elements, as H is the lightest. As the oscillations determine conventional superconductivity – and do this more effectively the faster the atoms oscillate – materials with high H content have high transition temperature. The strong bonds between the atoms also increase the temperature at which a material becomes superconducting. These conditions are met in H3S, and it is this compound that develops from H2S at high pressure.
The Mainz-based researchers are now looking for materials with even higher transition temperatures. At even higher temperatures the electron structure changes so the transition temperature begins to decrease. “An obvious candidate for a high transition temperature is pure hydrogen,” said Eremets. “It is expected that it would become superconductive at room temperature under high pressure.”
“There may be polymers or other hydrogen-rich compounds that can be converted to metals in some other way and become superconductive at room temperature,” said the physicist. If such materials can be found, we would finally have superconductors that can be used for a wide range of technical applications.” http://www.uni-mainz.de/presse/19539_ENG_HTML.php
The apparatus the team led by Dr. Mikhail Eremets at the Max Planck Institute for Chemistry in Mainz uses to generate extremely high pressures is amazingly handy. The researchers press the metal cell with Allen screws together. Only diamonds can resist the high pressure thus created in the center of the cell The gems operate like anvils that compress a sample. Credit: ©: Thomas Hartmann
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