Superconductors are materials capable of carrying electric current without any resistance, a characteristic that makes them valuable for many technological applications. Until recently, this extraordinary phenomenon (in the literal sense of the term - that which is beyond our ordinary experience) only occurred at extremely low temperatures, close to absolute zero.
The discovery of hydrogen-rich compounds like hydrogen sulfide (H₃S) has changed the game by enabling superconductivity at much more accessible temperatures, around -94°F (-70°C), thus opening new perspectives for practical use.
Extreme cold is necessary to achieve superconductivity.
Credit: University of Rochester / J. Adam Fenster
However, studying these materials presents major difficulties, particularly because they can only be created under colossal pressures, exceeding a million times normal atmospheric pressure. These extreme conditions make it impossible to use traditional measurement techniques, which long prevented researchers from deeply exploring the quantum mechanisms at work in these new-generation superconductors.
To overcome this obstacle, a team from the
Max Planck Institute in Mainz developed an innovative spectroscopic method capable of functioning under these exceptional pressures. This tunneling spectroscopy technique allowed for the first time to directly probe the superconducting state in H₃S, revealing the presence of a characteristic energy barrier of about 60 millielectronvolts.
The researchers also studied the deuterated version of this compound, D₃S, where hydrogen is replaced by its heavier isotope. The measurement of a smaller energy barrier, about 44 millielectronvolts, confirms that atomic lattice vibrations play a central role in the superconductivity mechanism. This experimental validation supports long-established theoretical predictions about electron behavior in these materials.
Dr. Feng Du, first author of the study published in
Nature, emphasizes that this technical breakthrough paves the way for a thorough understanding of the factors enabling high-temperature superconductivity. Mikhail Eremets, a pioneer in this field who recently passed away, considered this work the most important since the initial discovery of superconductivity in H₃S in 2015. His colleague Vasily Minkov adds that this advance brings us closer to designing superconductors that operate at room temperature.
The history of superconductivity dates back to 1911 with the discovery of this phenomenon in mercury by Heike Kamerlingh Onnes. For decades, it was believed that this extraordinary property could only exist at extremely low temperatures. The discovery of cuprates in the 1980s constituted a first revolution, followed more recently by the emergence of hydrogen-rich metal hydrides that constantly push temperature limits toward more practical values for future applications.
The phenomenon of superconductivity
Superconductivity represents one of the most remarkable properties that some materials can exhibit when cooled below a specific temperature. At this critical temperature, electrical resistance completely disappears, allowing current to flow indefinitely without any energy loss. This unique characteristic opens up technological breakthroughs for electricity transmission and storage, with potential applications ranging from ultra-efficient power grids to advanced propulsion systems.
The fundamental mechanism behind this phenomenon involves the formation of electron pairs, called Cooper pairs, which behave as a single entity. Unlike individual electrons in normal metals that undergo collisions with material atoms, these coordinated pairs move without encountering obstacles. This perfect coordination is made possible by subtle interactions with crystal lattice vibrations, creating a particularly stable collective quantum state.
The temperature at which a material becomes superconducting varies considerably depending on its composition and structure. The first discovered superconductors required cooling near absolute zero, severely limiting their practical applications. Recent progress has enabled the identification of materials that exhibit this property at much higher temperatures, some even approaching ambient conditions, representing a major advance toward broader use.
The importance of superconductivity extends far beyond the field of electricity, touching on cutting-edge technologies like medical magnetic resonance imaging, maglev trains, and quantum computers. Each new discovery in this field brings us a little closer to a future where energy could be transported and used with an efficiency that is unimaginable today.