Superconductors are extraordinary materials capable of carrying electrical current without any resistance, a property that has held immense promise for revolutionizing multiple technological fields. From lossless energy transmission and innovative magnetic levitation systems to the development of quantum computers, the impact of superconductivity could transform our understanding of energy and electronics. Yet, despite over a century of research, the practical use of superconductors has been deeply hindered by their need for extremely low operating temperatures, often far below what we encounter in everyday environments.
Traditionally, superconductivity has only manifested in materials cooled to temperatures hovering near absolute zero, rendering widespread application impractical and costly. Breakthroughs began to emerge in the late 20th century, with discoveries of high-temperature superconductors, such as copper-oxide ceramics, which can superconduct at temperatures above the boiling point of liquid nitrogen (77 K). Although this was a significant leap, the ultimate goal remained elusive: superconductivity at or near room temperature under manageable conditions.
A transformative development came with the advent of hydrogen-rich metallic compounds, particularly hydrogen sulfide (H₃S) and lanthanum decahydride (LaH₁₀). These materials demonstrate superconductivity at unprecedentedly high temperatures of 203 Kelvin (-70°C) and 250 Kelvin (-23°C), respectively, when subjected to enormous pressures exceeding one million times atmospheric pressure. These transition temperatures, well above that of liquid nitrogen, have captivated researchers worldwide, ushering in a new class of "high-temperature" superconductors that hint at the possibility of room-temperature superconductivity.
Central to understanding this phenomenon is the superconducting gap, a quantum mechanical property that defines the energy required to break the electron pairs—known as Cooper pairs—that facilitate resistance-free conductivity. This gap acts as a fingerprint of the superconducting state, offering critical information on the strength and nature of the interaction between electrons and lattice vibrations (phonons). Unraveling the precise characteristics of this gap is vital for decoding the mechanism underpinning superconductivity in these sophisticated materials.
However, probing the superconducting gap in hydrogen-rich compounds like H₃S presents a formidable challenge. Their synthesis demands extremely high pressures, conditions that render conventional measurement techniques such as scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy ineffective. The extraordinary environment makes direct experimental access to the superconducting state tremendously difficult, limiting understanding of these materials’ microscopic properties.
Addressing this barrier, scientists at the Max Planck Institute in Mainz developed a novel planar electron tunneling spectroscopy method capable of operating under such extreme conditions. This breakthrough technique was successfully applied to H₃S, marking the first direct observation of its superconducting gap. This accomplishment not only provides vital experimental validation for theoretical models but also opens the door to comprehensive studies of other complex hydride superconductors created under ultrahigh pressures.
The experimental data reveal that H₃S possesses a fully open superconducting gap measuring approximately 60 millielectronvolts (meV), a value that strongly signifies a robust pairing mechanism. In comparison, the deuterium analogue D₃S exhibits a smaller gap around 44 meV. Deuterium’s heavier isotope nature confirms that electron-phonon coupling is the driving force behind superconductivity in these systems, affirming longstanding theoretical predictions regarding lattice vibrations facilitating electron pairing in hydrides.
This discovery provides pivotal insights into the fundamental mechanisms of hydrogen-based high-temperature superconductors. By confirming phonon-mediated electron pairing through isotope substitution, researchers can better understand the requisites for high critical temperatures. Importantly, this knowledge forms a solid groundwork upon which scientists can explore new hydrogen-rich materials with the potential to reach or even exceed room temperature superconductivity.
The implications of this progress extend beyond pure science. Unlocking room-temperature superconductivity could enable transformative applications, such as highly efficient power grids free from transmission losses, ultra-compact and fast quantum computers, and revolutionary magnetic levitation transport systems. The key lies in engineering materials that sustain superconductivity at ambient pressures, making them accessible and practical beyond specialized laboratory conditions.
Leading figures in the field have heralded this research as a watershed moment. The late Dr. Mikhail Eremets, a pioneer recognized for his seminal work on high-pressure superconductivity, described the study as the most significant since the initial discovery of superconductivity in H₃S in 2015. His visionary work laid the foundation for exploring hydrogen-rich compounds under pressure as promising routes toward high-temperature superconductivity, a dream now one step closer to reality thanks to these new findings.
Dr. Vasily Minkov, head of High-Pressure Chemistry and Physics at the Max Planck Institute for Chemistry, emphasized that this advancement aligns perfectly with Eremets’ decades-long vision of pragmatic superconductors operating at manageable pressures and temperatures. The refined tunneling technique is poised to become a critical tool for future explorations, enabling systematic investigations across a broader range of hydrides and beyond.
Fundamentally, the superconducting gap encapsulates the quantum essence of the superconducting phase. When electrons form Cooper pairs at temperatures below the critical temperature (T_c), they condense into a macroscopic quantum state with zero electrical resistance. The gap quantifies the energy threshold to disrupt these pairs, directly linking to the material’s superconducting robustness. Its symmetry and magnitude provide vital clues about the nature of electron interactions and pairing mechanisms, insights that are indispensable for material design.
Since the initial discovery of superconductivity in mercury by Heike Kamerlingh Onnes in 1911, scientific understanding has continuously advanced. The high-temperature cuprates discovered by Bednorz and Müller in the 1980s shattered earlier paradigms but still fell short of room temperature operation. Hydrogen-rich hydrides, through their distinctive lattice dynamics and electron-phonon interactions under pressure, represent the cutting edge of this quest, suggesting that room-temperature superconductivity may finally emerge within reach.
Looking ahead, researchers aim to extend the new tunneling spectroscopy technique to study additional hydride superconductors and other exotic compounds synthesized at ultrahigh pressures. The nuanced information gained from detailed gap measurements will illuminate the pathways to optimize electron pairing and material stability. This scientific journey holds the promise of uncovering materials with the ideal balance of temperature, pressure, and practical usability for future technologies.
In essence, this pioneering study heralds a new chapter in superconductivity research by providing the first direct measurement of the superconducting gap in H₃S under extreme conditions. It validates theoretical frameworks and solidifies our understanding of the quantum state in high-temperature hydrides. The aspiration for widespread, ambient-condition superconductors, once a distant dream, edges closer to tangible reality, promising profound technological impact in the upcoming decades.
Subject of Research: Not applicable
Article Title: Superconducting gap of H3S measured by tunnelling spectroscopy
News Publication Date: 23-Apr-2025
Web References: http://dx.doi.org/10.1038/s41586-025-08895-2
References: Nature, DOI: 10.1038/s41586-025-08895-2
Image Credits: Not provided
Keywords
Superconduction, Room temperature, Hydrogen
