Academician Chen Xianhui, a member of the Chinese Academy of Sciences, has been deeply involved in the field of superconductivity for over 30 years. He has been dedicated to exploring novel unconventional superconductors and studying the physics of superconductivity and strong correlation. His research has led to a series of internationally influential discoveries in unconventional superconductors and functional materials, including the identification of iron-based superconductors and organic superconductors. These achievements, characterized by systematic and innovative contributions, establish him as one of the globally impactful scientists in this field.
In the movie "Avatar," the breathtaking floating mountains of Hallelujah in the clouds astonish viewers. What mysterious force allows these mountains to suspend in mid-air? It's attributed to a miraculous room-temperature superconductor ore that utilizes powerful magnetic fields to levitate the Hallelujah mountains. But what exactly are superconducting materials? And why do they possess such formidable magnetic levitation capabilities?
Superconductivity is a peculiar physical phenomenon. Unlike ordinary conductors that exhibit electrical resistance and dissipate energy as heat, superconductors, under extremely low temperatures, display the astonishing property of zero electrical resistance. Not only do they conduct electricity without loss, but they also manifest a range of remarkable characteristics, transforming into extraordinary materials.
In 1896, scientist James Dewar liquefied air, primarily nitrogen, achieving temperatures close to -200 degrees Celsius. Curious about the behavior of matter at such frigid temperatures, he observed the electrical resistance of mercury but found it remained finite, disappointing his expectations. Thirteen years later, Dutch physicist Heike Kamerlingh Onnes successfully liquefied the last remaining gas, helium, reaching a temperature of 4.2 Kelvin. Astonishingly, at around 4.2 Kelvin, the electrical resistance of mercury abruptly vanished. Recognizing this as a new physical state, Onnes coined the term "superconductivity," marking the birth of superconductors.
In 1962, Anderson and Rowell demonstrated another defining characteristic of superconductivity: zero resistance. They passed a current through a superconducting coil and then disconnected the power source, observing no decay in the current. This proved that superconductors exhibit zero resistance, marking the first distinctive feature of superconductivity. Another remarkable trait is complete diamagnetism. In 1933, scientists Meissner and Ochsenfeld discovered that superconductors, such as tin (with a superconducting temperature of 3.7 K), expel magnetic fields from their interior. Prior to the discovery of superconductors, it was believed that magnetic fields could penetrate any material, including living organisms. However, when in a superconducting state, the magnetic flux inside remains zero, demonstrating its second unique property.
Furthermore, superconductors exhibit a phenomenon known as magnetic flux quantization, crucial for achieving magnetic levitation. When impurities or defects are present in a superconductor and an external magnetic field surpasses a certain threshold, a small amount of magnetic flux penetrates the interior and becomes pinned near the defects, resembling being "nailed" in place. This phenomenon, called "flux pinning," enables stable interaction between the superconductor and the external magnetic field, facilitating magnetic levitation. The "pinning effect" plays a pivotal role in the design and application of superconducting magnetic levitation systems, providing excellent stability and disturbance resistance.
Electricity powers various devices, from electric kettles running continuously for an hour to stereos operating for 30 hours. The transmission of every kilowatt-hour of electricity in cities relies on electrical cables. However, conventional cables possess resistance, resulting in significant energy losses during transmission, typically ranging from 5% to 10%. As transmission distances increase, so does the loss rate. With the advent of the world's strongest 35-kilovolt superconducting cables, the challenge of power line losses has been overcome. Empowered by "superconducting technology," these cables achieve nearly zero resistance. Compared to traditional transmission methods, under full load conditions, they can successfully transmit 2160.12 amperes of current with a 35-kilovolt "small" cable, matching the transmission capacity of a 220-kilovolt "large" cable, significantly reducing the space required for constructing high-voltage substations. What other miraculous applications do superconducting materials hold? Today's society revolves around three key technologies: energy, information, and biotechnology. Superconducting materials, by bridging energy and information technologies, have laid the groundwork for extensive applications. Superconductivity is poised to strategically replace existing power transmission technologies. There are two main applications of superconductors: high-power and low-power applications. High-power applications relate to energy, transportation, and biomedical fields, while low-power applications involve superconducting quantum interferometers, quantum bits, and quantum computing. Overall, superconductivity represents a strategic scientific technology capable of profound transformations in energy and information sectors.
Currently, applied superconducting materials fall into two categories: high-temperature superconductors (HTS) and low-temperature superconductors (LTS). Both require extremely low temperatures to achieve superconductivity, with critical temperatures ranging from 25K to 30K (-248°C to -243°C) for LTS. LTS demands even lower temperatures and typically operates in expensive liquid helium environments. Despite their applications in various fields such as magnetic resonance imaging, particle accelerators, and maglev trains, the expensive cooling agents limit their widespread use. In contrast, HTS operates in relatively cheaper liquid nitrogen environments, offering broader application potential.
What surprises will room-temperature superconductivity bring to the world?
If we were to list the major events that captivated the global tech community in 2023, room-temperature superconductivity would undoubtedly feature prominently. This buzz around room-temperature superconductivity was ignited by American scientist Diaz. On March 8, 2023, Diaz announced at the American Physical Society meeting that room-temperature superconductivity had been achieved under 1 gigapascal (GPa) of pressure, stunning the audience. Prior research in the past five years had been conducted at pressures exceeding 200 gigapascals (GPa), equivalent to the pressure at the Earth's core, highlighting the monumental achievement of Diaz's team in significantly reducing the pressure required. This announcement sent shockwaves through the global tech community. The excitement continued on July 22, 2023, when a South Korean team claimed to have discovered room-temperature superconductor material LK-99, further fueling the superconductivity frenzy. However, this excitement was short-lived as both Diaz's and the Korean team's discoveries were later retracted due to inability to reproduce the results. Despite this setback, the global scientific community's intense interest in room-temperature superconductivity persists. But what surprises does room-temperature superconductivity hold for the world?
Room-temperature superconductivity represents a groundbreaking technological advancement because it diverges significantly from traditional superconductivity. Traditional superconducting materials only exhibit superconductivity at extremely low temperatures, limiting their practical applications. For instance, cuprate superconductors require temperatures around -135°C, achievable with liquid nitrogen cooling. Room-temperature superconductivity, on the other hand, promises superconductivity at ambient temperatures, eliminating the need for specialized cooling systems. If achieved, room-temperature superconductivity could revolutionize energy utilization, accelerate transportation, and enhance computational speed like never before.
Will room-temperature superconductors be discovered? From a physics standpoint, there's no theoretical barrier preventing room-temperature superconductivity. Moreover, macroscopic quantum effects, like those observed in graphene's integer quantum Hall effect, suggest the feasibility of observing macroscopic quantum phenomena at room temperature. Additionally, considering that copper-based superconductors have achieved critical temperatures of 135K (-138.15°C), doubling this temperature to 270K (-3.15°C) seems plausible from an energy scale perspective. However, practical challenges must be addressed incrementally. Despite the vast potential of superconductivity, its limited application is due to supporting technologies, cooling requirements, and cost considerations. Room-temperature superconductivity, by eliminating the need for cooling, could vastly expand its applications, making it a pivotal technology in both energy and information sectors.
Superconductivity research entails three main tasks: explaining unconventional superconductivity mechanisms in materials like cuprates and iron-based superconductors, exploring materials suitable for practical applications or achieving higher critical temperatures, and widespread application of superconductors. Challenges like superconducting quantum computers, superconducting chips, high-power and high-magnetic-field applications are considered Nobel Prize-worthy endeavors. Material discoveries have historically driven technological revolutions, and room-temperature superconductors could serve as potent candidates for the next wave of innovation. The immense societal interest in room-temperature superconductivity stems from its potential to support the next generation of civilization across scientific research, information computing, communication, biomedical, power, transportation, and energy sectors. The discovery of room-temperature superconductors, along with controlled nuclear fusion, could permanently solve humanity's energy challenges. Prospects of Superconductor Research
One outlook for superconductor research is to overcome the technological bottlenecks of semiconductors. Despite the advancements in semiconductor technology, integrated circuits have reached sub-10-nanometer levels. However, there are several bottlenecks within semiconductor technology: computing speed, power consumption, and manufacturing. Currently, manufacturing bottlenecks, exemplified by issues with lithography machines, such as those from ASML in the Netherlands, dominate discussions. Yet, power consumption presents another significant bottleneck. The immense power requirements of supercomputers lead to exorbitant electricity bills, hindering sustainable development. Addressing power consumption is paramount for the semiconductor industry. Many of China's data centers are situated in the northwest due to advantages like lower average temperatures and energy costs. Power consumption involves two aspects: chip operation generates heat, necessitating efficient heat dissipation. Traditional cooling methods, like fans, face challenges with temperature regulation. Superconductors offer lower power consumption, potentially easing heat dissipation and reducing costs. Technologies like artificial intelligence and ChatGPT heavily rely on supercomputers, exacerbating power consumption concerns. Superconductors offer a promising solution in this regard, providing significant advantages in speed, power efficiency, manufacturing, and ecological impact. Superconductor digital computers, as seen with the U.S.'s Titan, represent a step towards post-Moore's Law information technology. The application of superconducting technology is poised to revolutionize industries such as energy, power transmission, transportation, and healthcare, driving profound changes in human civilization. We eagerly anticipate the realization of room-temperature superconductivity, propelling the advancement of human civilization.
