High-temperature superconductivity

Some things can move power with no loss.

These special things must stay very cold. Some need a very expensive liquid to stay cold. But new ones work with liquid nitrogen. This liquid is easier to use. These new things are often made of ceramics. Ceramics are like hard plates or bowls. They can be easy to break. These materials can also work in strong magnets. They help us build better tools. It is a big discovery for science.

Some materials can move power without losing any. This is called superconductivity. Most superconductors only work when they are extremely cold. They need liquid helium to stay at that temperature. Liquid helium is hard to handle and costs a lot.

In 1986, Georg Bednorz and K. Alex Müller found something new. They found a way to make ceramics act as superconductors. These are called high-temperature superconductors. They are "high-temperature" because they work above the boiling point of liquid nitrogen.

Using liquid nitrogen is much easier and cheaper than helium. These materials also work well in strong magnetic fields. This helps us build better magnets. Many of these materials are cuprates. Cuprates are copper oxides mixed with other metals.

One type is called YBCO. It uses yttrium, barium, copper, and oxygen. Most high-temperature superconductors are ceramics. Ceramics are often brittle. This means they can break easily. This makes it hard to turn them into long wires.

Superconductivity is a special way that some materials move electricity. In these materials, power flows without losing any energy at all. Most superconductors only work when they are extremely cold. They usually need liquid helium to stay at those freezing temperatures. Liquid helium is very expensive and hard to handle.

High-temperature superconductors are different and very important. They are called "high-temperature" because they work above the boiling point of liquid nitrogen. This makes them much easier and cheaper to use for science and technology.

These materials work through a specific way it works called a transition. A material has a critical temperature, which is the temperature below which it becomes a superconductor. When the material gets colder than this limit, it changes how it behaves. Many of these materials are ceramics, which are hard materials like pottery. Most high-temperature superconductors are cuprates, or copper oxides mixed with other metals. They are also Type-II superconductors. This means they allow magnetic fields to pass through them in tiny tubes or holes.

Scientists have been searching for these materials for a long time. Superconductivity was first discovered by Kamerlingh Onnes in 1911 in a metal solid. In 1986, researchers Georg Bednorz and K. Alex Müller found something new at an IBM lab. They discovered superconductivity in a ceramic called lanthanum barium copper oxide. This was a huge breakthrough for science. Because of this discovery, Bednorz and Müller won the Nobel Prize in Physics in 1987.

There are many different types of these special materials. One famous class is called REBCO, which stands for rare-earth barium copper oxides. An example is YBCO, which uses yttrium, barium, copper, and oxygen. Another group is called iron-based compounds, discovered in 2006 by Hosono and his coworkers. Some materials like magnesium diboride can be easy to make. However, it only works below 39 K, so it cannot use liquid nitrogen.

Other materials like lanthanum hydride work only under huge pressure.

Understanding these materials helps us build amazing tools. One big use is making superconducting magnets. These materials can stay superconducting even in very strong magnetic fields. This is a major advantage over older materials. However, making them can be a hard job because ceramics are brittle. This means they can break easily, which makes it tough to turn them into long wires. Scientists are still working hard to find a superconductor that works at room temperature.

High-temperature superconductivity refers to a state where certain materials conduct electricity with zero resistance at relatively high temperatures. In physics, a superconductor is a material that allows electrical current to flow without losing any energy to heat. Most traditional superconductors only function at temperatures near absolute zero. They require expensive coolants like liquid helium to maintain these extreme conditions. High-temperature superconductors, or HTS, are defined as materials with a critical temperature above the boiling point of liquid nitrogen. This threshold is significant because liquid nitrogen is much cheaper and easier to handle than liquid helium.

The mechanism of superconductivity involves a material reaching a specific critical temperature. Once the material drops below this temperature, it undergoes a transition into a superconducting state. Most HTS materials are classified as Type-II superconductors. Unlike Type-I superconductors, which expel all magnetic fields through the Meissner effect, Type-II materials allow magnetic fields to penetrate their interior. This penetration happens in quantized units of flux, creating tiny tubes or holes of normal metallic regions within the superconducting bulk. This unique property allows Type-II superconductors to remain functional even when exposed to very high magnetic fields.

Scientists categorize high-temperature superconductors into several distinct classes. The largest group consists of cuprates, which are copper oxides combined with other metals. A major sub-class of cuprates is the rare-earth barium copper oxides, known as REBCOs. An example is yttrium barium copper oxide, or YBCO, which contains yttrium, barium, copper, and oxygen. Another important class is the iron-based compounds, which were discovered in 2006. Some materials, like magnesium diboride, are sometimes included in this category. While magnesium diboride is simple to manufacture, it only superconducts below 39 K. This makes it unsuitable for liquid nitrogen cooling, which requires a higher temperature.

The history of this field began in 1911 when Kamerlingh Onnes discovered superconductivity in a metal solid. For decades, researchers searched for materials that worked at higher temperatures. A massive breakthrough occurred in 1986 at an IBM research lab near Zürich, Switzerland. Researchers Georg Bednorz and K. Alex Müller discovered superconductivity in a ceramic called lanthanum barium copper oxide (LBCO). This discovery showed that superconductivity could exist in ceramic materials rather than just metals. For this achievement, Bednorz and Müller were awarded the Nobel Prize in Physics in 1987.

Following the 1986 discovery, scientists found ways to increase the critical temperature of these ceramics. While the original LBCO had a transition temperature of 35 K, modifying the material to create YBCO raised that temperature above 90 K. Today, the mercury, barium, and calcium cuprate holds the record for the highest transition temperature at ambient pressure, reaching approximately 133 K. Other materials like lanthanum superhydride reach even higher temperatures, such as 250 K. However, these high temperatures only occur under extreme pressures of 170 gigapascals. Researchers are also exploring new frontiers, such as bilayer graphene. In 2018, scientists found superconductivity in graphene when one layer was twisted at an angle of 1.1 degrees.

Despite their advantages, high-temperature superconductors present significant engineering challenges. Most HTS materials are ceramics rather than metals. While ceramics are excellent for superconductivity, they are also very brittle. This brittleness makes it difficult to manufacture them into long, flexible wires for practical use. Additionally, HTS materials do not form large, continuous superconducting domains. Instead, they consist of clusters of microdomains where superconductivity occurs. This characteristic makes them less suitable for certain applications, such as magnets for magnetic resonance spectrometers, which require actual superconductive currents.

The significance of HTS research lies in its potential for advanced technology. One primary application is the construction of superconducting magnets. HTS materials are highly valuable here because they can retain superconductivity in much higher magnetic fields than previous materials. Some cuprates can withstand an upper critical field of about 100 tesla. This capability is essential for creating powerful magnets used in various scientific and industrial tools. As researchers continue to study the theoretical foundations, such as the resonating valence bond theory, the goal remains to find a superconductor that works at room temperature and ambient pressure.