Chapter 1: The Dawn of Discovery

In May 2014, we stumbled upon a significant breakthrough. During our experiments, we assessed the electrical characteristics of a pellet confined between two diamonds within an anvil. This device was capable of exerting a staggering pressure of 2 million atmospheres, approximately half that found at the Earth's core. Theoretical models suggested that under such extreme pressures, alongside temperatures ranging from 123 degrees Celsius to -73 degrees Celsius, metallic hydrogen could exhibit zero electrical resistance, effectively becoming a perfect conductor.

The implications of this discovery are enormous. Achieving true room-temperature superconductivity could revolutionize energy transmission, facilitate rapid train travel, enable magnetic levitation, and foster advanced computing technologies. However, reaching superconductivity at room temperature remains elusive. At the time of our experiments, no materials had shown superconductivity above -130° C under standard pressures.

Motivated by the theoretical predictions, we embarked on a quest to identify a hydrogen-rich chemical compound. Our initial attempts with silane—a compound of four hydrogen atoms bonded to one silicon atom—yielded superconductivity only at a frigid -256 C, far from impressive.

Unexpectedly, superconductivity was discovered in cuprate systems, which caught the scientific community off guard. Our attention shifted to hydrogen sulfide, a compound of hydrogen atoms arranged in a lattice with sulfur. Theoretical predictions indicated that it would become superconducting at -193° C, which was still not very encouraging. Additionally, hydrogen sulfide is toxic and possesses a pungent odor, leading to its use as an odorant in natural gas for leak detection.

Nevertheless, hydrogen sulfide was accessible, and we prepared a minuscule pellet, roughly the diameter of a human hair. On May 17, we observed a transition to superconducting behavior—zero resistivity—at a temperature of -223 C, colder than expected and significantly below the best-performing superconductors known at the time.

With this promising result, we diligently sought to replicate our findings. Over the next three months, we maintained temperatures around -220 C, meticulously examining our superconducting system and experimenting with varying pressures and temperatures. Then, fortune smiled upon us.

The evolution of superconductivity is marked by serendipitous discoveries and unexpected turns. Kamerlingh Onnes, who was awarded a Nobel Prize for his pioneering work in superconductivity, was initially not in search of it. His goal was to demonstrate that metallic resistance would gradually diminish to zero as the temperature approached absolute zero. Instead, he witnessed a sudden drop in resistance of solid mercury at just 4 degrees above absolute zero. Furthermore, he was the first to observe helium transitioning into a superfluid, a phenomenon he overlooked, which later earned Pyotr Kapitsa a Nobel Prize in 1937.

The discovery of superconductivity in cuprates was equally unforeseen. Researchers focused on increasing the superconducting transition temperature of metal alloys for years, never anticipating that cuprates would ultimately dominate high-temperature superconductivity records, achieving temperatures around -135 C.

Our own strokes of luck came in multiple instances. On August 22, a malfunction in the pressure mechanism of one of our diamond cells compelled us to heat our sample. As we monitored the incoming data, we were astonished to find the resistance of the sample decreasing with rising temperatures! The superconducting transition temperature was much higher than previously anticipated, reaching -120 C.

This revelation prompted us to re-evaluate our earlier data. Upon review, we discovered faint signs of superconducting transitions occurring as high as -100° C—a new world record. Although these initial measurements were not optimal, utilizing three electrical contacts instead of the four needed for precise data, they hinted at a groundbreaking phenomenon within our sample.

Subsequently, we learned that our hydrogen sulfide (H²S) pellet was unexpectedly dissociating into sulfonium (H³S), a detail overlooked by theoretical models. This dissociation was crucial, as the hydrogen atom in sulfonium was compressed by surrounding sulfur atoms, a process known as chemical compression, effectively amplifying the pressure applied. Remarkably, sulfonium could still be regarded as metallic atomic hydrogen, allowing us to align our findings with theoretical predictions for that material. Approximately 92% of its superconducting properties stemmed from the configuration of its hydrogen atoms, with only 8% attributable to the sulfur atoms maintaining their structure.

As we persisted with our experiments, we observed increasingly higher transition temperatures. The previous maximum of -110 C had been achieved by a cuprate under pressure. Our methodology led us to a remarkable transition temperature of -70° C.

While -70° C is still extremely cold, it is a significant advancement from the initial -269° C benchmark. Notably, temperatures of -70° C can be found outdoors in various regions, such as Yakutsk, Russia, where a record low of -64° C has been documented. For some, this may even be perceived as room-temperature superconductivity—more accurately described as street-temperature superconductivity. With continued effort, we hope to explore warmer locales in the future.

Mikhail Eremets and Alex Drozdov are physicists affiliated with the Max Planck Institute for Chemistry in Germany.

Chapter 2: The Future of Superconductivity

The first video titled "The Map of Superconductivity" provides an insightful overview of the landscape of superconducting materials and their potential applications.

The second video, "RUSSIAN Gas Power of Siberia 2 Pipeline Deal with China Collapses as China Moves Towards Hydrogen," discusses the implications of energy transitions and the geopolitical landscape surrounding hydrogen technology.