New York-based scientists have achieved the room-temperature superconductivity for the first time, using a hydrogen, carbon, and sulfur compound. According to the study published in Nature, the new compound operates as a superconductor at up to 15 °C (59 °F) at very high pressure (267 GPa between a pair of diamond anvils – that’s about 75% of the pressures those found in the Earth’s core). That’s 38 °C hotter than the previous high-temperature superconductivity record set in 2019, also at very high pressure (170 GPa).

Since the new compound operates as a superconductor only at extremely high temperatures, it’s not suitable for practical use. But, some characteristics of the new compound boost hopes that one day the right combination of atoms might be discovered. Now, materials scientists face the challenge of finding a superconducting compound that not only functions at normal temperatures but also under regular pressures.

What is superconductivity?

Superconductivity

Superconductivity is a phenomenon whereby an electric current moves through a material without any resistance (without any loss). These materials are called “superconductors”, and they conduct electricity without resistance and could therefore revolutionize electronics and power grids. The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes (21 September 1853 – 21 February 1926).

Room-temperature superconductivity: a long-sought goal

Superconductors conduct electricity without resistance and could therefore revolutionize electronics and power grids. So far, however, the resistance-free (means loss-free) flow of electrons only worked with deep-frozen materials. Now, for the first time, researchers have succeeded in making a material superconducting at room temperature – but, unfortunately, at extremely high pressures.

Superconductivity gives materials two decisive properties: First, their electrical resistance disappears, so that in this state they conduct electrons without loss. On the other hand, they repel magnetic fields, which deflect magnetic field lines around the material. This allows superconductors to float on a magnetic field – and this in turn enables applications such as magnetic levitation trains.

Superconductors are also used in particle accelerators, in magnetic resonance tomography, or in quantum computers. So far, however, these superconductors have only lost their electrical resistance at ultra-cold temperatures, so they have to be cooled in a complex manner – for example with liquid nitrogen or helium. The cost of keeping these materials at very cold temperatures is so high.

Room-temperature superconductivity experiment setup
In this experimental setup, the researchers from the United States achieved the room-temperature superconductivity. (Image: Adam Fenster)

That is why scientists have been looking for decades for materials that turn into superconductors with little cooling or even at room temperature. They achieved initial successes with high-temperature superconductors such as cuprates, copper compounds that become superconducting at temperatures as low as minus 100 degrees Celcius (minus 148 °F).

In 2015, a group of researchers achieved an important breakthrough with a completely new type of superconductor: under very high pressure (155 gigapascals -GPa-, more than 1 million times Earth’s atmospheric pressure at sea level), they made hydrogen sulfide (H2S) become superconductor at -70 °C (-94 °F).

Scientists attribute this primarily to the properties of hydrogen. Physicist Ranga P. Dias of the University of Rochester, the lead author of the study explains: “To create a high-temperature superconductor, you need strong bonds and light elements – hydrogen is the lightest atom and the hydrogen bond is one of the strongest”.

Based on this, other teams have since made compounds of metals and hydrogen into superconductivity and gradually raised the transition temperature. The previous record was set in 2019 by a team led by Mikhael Eremets from the Max Planck Institute for Chemistry in Mainz with a lanthanum hydride. Under extremely high pressure, this material became superconducting at 250 K (-23 degrees Celsius or -9.4 °F).

Dias and his colleagues think they could push the Tc (critical temperature, where the material becomes a superconductor) up even higher by adding a third element: carbon, which forms strong bonds with neighboring atoms.

A superconductor is generally considered high-temperature if it reaches a superconducting state above a temperature of 30 K (-243.15 °C or -405.67 °F).

Still not suitable for everyday use

The decisive breakthrough to superconductors at room temperature been achieved only came now. To achieve this, Dias and her colleagues took hydrogen sulfide as the starting material and added hydrogen and methane (CH4) to it. Under an initially comparatively moderate pressure of around 4 gigapascals, these components react with one another and a crystalline compound is formed, in the lattice of which methane replaces some of the hydrogen sulfide molecules. In addition, inclusions filled with hydrogen arose in the crystal.

When this carbon-containing sulfur-hydrogen compound was put under further pressure, it switched to the superconducting state at around 267 gigapascals and a temperature of 14.55 °C (58.19 °F). This is the first time that any material has been made superconductive at a temperature above zero degrees.

Because of the need for extremely high pressures, the new method is still not suitable for everyday use. But, researchers emphasize that this temperature leap, by ~50 K, from the previous Tc record of 203 K indicates the real possibility of achieving RTSC (room-temperature superconductivity) in the future at ambient pressure, which could transform daily life.

Sources

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