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A superconductor is a material that permits electric current to pass through it without experiencing any energy loss. Standard conductors, like copper wires, possess a level of electrical resistance — this is what causes them to heat up when an electric current passes through them.
In contrast, superconductors exhibit zero resistance, so they do not heat up when current flows through them. This phenomenon, known as superconductivity, is deeply rooted in quantum mechanics.
History
The concept of superconductivity was first discovered in 1911 by Heike Kamerlingh Onnes, a Dutch scientist who was studying low-temperature physics. Onnes discovered that as he cooled mercury to temperatures just a few degrees above absolute zero, mercury was able to conduct electric current without any resistance or energy loss.
Onnes’ experiments and discoveries became part of the foundation that later physicists built upon: At extremely low temperatures, quantum mechanical effects become more pronounced, and the behavior of electrons becomes governed by quantum laws rather than classical physics.
How Superconductors Work
Most materials need to be in a very low-energy state to be superconductive.
When an electric current passes through a standard conductor like copper at room temperature, the electrons that are navigating through the copper’s lattice of atoms can interact with vibrations in the lattice. This interaction results in resistance, which leads to the dissipation of energy in the form of heat.
When an electric current passes through a conductor at an extremely cold temperature, however, the electrons can form pairs that move through the conductor’s lattice of atoms as if they were a single entity. This severely reduces or even eliminates the electrons’ ability to interact with vibrations in the lattice.
This lack of interaction with lattice vibrations (phonons) is an important factor that contributes to the absence of electrical resistance in superconductors.
Type I and Type II Superconductors
There are two categories of superconductors: Type I and Type II. A Type I superconductor is comprised of conductive elements that have a critical temperature ranging from 0.000325 K to 7.8 K at standard pressure. In contrast, Type II superconductors are comprised of mostly metallic alloys and compounds which become superconductive at higher temperatures.
The main difference between Type I and Type II, however, is how they respond to magnetic fields. Type I superconductors expel all magnetic flux below a certain critical field, while Type II superconductors can accommodate some magnetic flux within specific ranges.
The Meissner effect, in which a superconductor will expel virtually all magnetic fields from its interior when cooled below a certain critical temperature, is a phenomenon observed in both Type I and Type II superconductors. However, the Meissner effect behaves differently in Type I and Type II superconductors.
- Type I: In Type I superconductors, which are usually elemental superconductors like lead and mercury, the Meissner effect is very pronounced. This type of superconductor exhibits a sharp transition from its normal state to a superconducting state and pushes away magnetic fields entirely when temperatures drop below the transition point.
- Type II: In type II superconductors, which are often compound materials, the transition from normal state to superconducting state is gradual. Most use cases and practical applications of superconductors today rely on Type II superconductors because they can tolerate stronger magnetic fields before transitioning from the superconducting state back to the normal state.
Room Temperature Superconductors
Despite the incredible potential of superconductivity, there are important challenges associated with the practical implementation of superconductors. One of the biggest challenges is the expense. Current superconductors require energy-intensive cooling methods to achieve and maintain low temperatures.
To address this challenge, scientists have been searching for new compounds that can exhibit superconductivity at (or near) room temperature.
In their research, some theoretical physicists are using advanced computational methods like quantum simulations to model the behavior of materials under extreme conditions and identify potential candidates for room-temperature superconductivity.
Although there have been a few research papers that have gotten people excited, so far, no materials are known to exhibit superconductivity at or near room temperature (around 20-25°C or 68-77°F).
Use Cases for Superconductors Today
Today, superconductors are used to make powerful and efficient electromagnets for various applications.
An electromagnet is a type of magnet created by running an electric current through a conductive material. The electric current generates a magnetic field around the material, effectively turning it into a temporary magnet. The strength of the magnetic field produced by an electromagnet can be controlled by adjusting the amount of current flowing through the material and turning it on and off as needed.
Superconducting magnets offer stronger and controllable magnetic fields compared to conventional magnets. They are highly energy-efficient because of zero resistance, which makes them cost-effective for continuous use.
Their benefits span medical, research, and transportation fields, including:
- Magnetic Resonance Imaging (MRI): Superconducting magnets are used in MRI machines to create strong and stable magnetic fields for medical imaging.
- Particle Accelerators: Superconducting radiofrequency cavities are used in particle accelerators like the CERN Large Hadron Collider (LHC) to accelerate particles to high energies more efficiently.
- Magnetic Levitation (Maglev) Trains: Superconducting materials enable maglev trains to float above the tracks, allowing for high-speed and energy-efficient transportation by reducing friction.
- Scientific Research: Superconductors are used in various scientific instruments and experiments, such as in high-energy physics experiments and nuclear magnetic resonance spectroscopy.
- Electromagnets for Fusion Research: Superconducting magnets are employed in experimental fusion reactors like tokamaks to confine and control plasma at extremely high temperatures.
- Magnetoencephalography (MEG): Superconducting sensors are used in MEG systems to map brain activity by measuring the magnetic fields generated by neural currents.
Examples
Here are some examples of superconductors in use today:
- Mercury: Becomes superconducting at -269 degrees Celsius (-452 degrees Fahrenheit).
- Niobium: Becomes superconducting at -245 degrees Celsius (-410 degrees Fahrenheit).
- Magnesium diboride: Becomes superconducting at -195 degrees Celsius (-319 degrees Fahrenheit).
- Yttrium barium copper oxide: Becomes superconducting at -92 degrees Celsius (-136 degrees Fahrenheit).
- Iron pnictides: Become superconducting at -55 degrees Celsius (-67 degrees Fahrenheit).
The Future of Superconductors
Superconductors can revolutionize power distribution systems by enabling the transfer of electricity over longer distances with minimal loss.
Other key applications include:
- Particle Accelerators: Large-scale particle accelerators, such as those used in particle physics research, require powerful magnetic fields to guide and control the paths of accelerated particles. Superconducting magnets enable the creation of stronger and more stable magnetic fields, enhancing the capabilities of these accelerators.
- Power Generation: Superconducting generators can potentially produce more electricity from the same input of mechanical energy and enable more sustainable and efficient energy production systems.
- Electronics: Superconductors can be used in certain types of electronic devices, such as superconducting quantum interference devices (SQUIDs), which are extremely sensitive magnetometers used in a variety of scientific and medical applications.
- Quantum computers: Superconducting qubits are promising candidates for building quantum computers. This could revolutionize computing by solving complex problems in fields like cryptography.
