Superconductors: the Search for Room-Temperature Zero-Resistance Materials
Driven by the promise of zero-resistance power transmission and the marvel of levitating trains, scientists tirelessly pursue the holy grail of room-temperature superconductors.
Conductors and insulators — two terms we use in our everyday lives. Conductors are materials that allow electrical current to flow through them easily, like metal wires. Insulators, on the other hand, are materials that resist the flow of electrical currents, like rubber or plastic.
But here’s something interesting — even though conductors allow current to flow through them, they’re imperfect. When current flows through a conductor, the moving electrons bump into atoms and lose energy. This loss of energy is called resistance, measured in ohms.
Properties of Superconductors
In the last century, the discovery of another type of material has fascinated scientists — superconductors. Superconductors have two main features — zero electrical resistance and the Meissner effect.
1) Zero electrical resistance: Certain materials, when cooled to a low temperature, lose all electrical resistance. These materials become perfect conductors, known as superconductors.
2) Meissner effect: When you bring a magnet close to a conductor, the electrons in the conductor feel this changing magnetic field, and start moving in a circle called an eddy current. This eddy current counteracts the magnetic field by generating its own magnetic field. In a normal conductor, this current dies away quickly because of electrical resistance. However, in a superconductor, the eddy currents circulate forever. This moving current generates a magnetic field, cancelling out the original magnetic field. This property, the Meissner effect, makes a superconductor magically levitate above a magnetic field (like the train in the image above).
Why care about superconductors?
Superconductors can generate high magnetic fields because you can circulate lots of current inside a superconductor which creates a magnetic field. This principle is used in the big tube in MRI machines and also in tokamak reactors for nuclear fusion. Superconductors are also already being used for levitating trains.
Room temperature superconductors can also help build transmission lines to transport electricity where no energy would be lost during transmission.
Challenges with current superconductors
Each superconducting material has a specific temperature and pressure value range in which it superconducts. However, no material studied so far can superconduct at room temperature and atmospheric pressure, making it expensive to generate the superconducting material.
High-temperature superconductors
In the last three decades, researchers discovered that even some insulators could be cooled down to become superconductors. As these materials superconducted at higher temperatures than before (even though it is way below room temperature), they are called high-temperature superconductors and it was revolutionary because you could now study them with just liquid nitrogen at 77 Kelvin = -196 C, which is way cheaper than the previously used liquid helium at 4 Kelvin = -269 C. For reference, the room temperature is about 295 Kelvin = 21 C.
These materials included cuprates (layers of copper oxide), pnictides (iron-based superconductors) and fullerenes (pure carbon-based organic superconductors). However, these materials still required extreme pressures to superconduct — similar to what we find inside Jupiter. To produce these pressures in our labs using a technology known as a diamond anvil cell, which involves pressing the material between two diamonds.
Superconducting Hydrides and Discovery of New Materials
In recent years, another set of materials called hydrides were discovered to be specifically good at becoming superconductors. In 2020, a room-temperature superconductor was claimed to be discovered which superconducts under a huge amount of pressure. However, this study was retracted because other scientists had trouble recreating their results. Retracting a paper in science is a huge deal because it breaks others’ trust inthe group. But now, the same team report superconductivity in another material — nitrogen-doped lutetium hydride with a maximum Tc of 294 K. This time, however, other scientists are confident that the analysis was thorough.
The team observed zero resistance in the material and showed that the material exhibited the Meissner effect. The material is bluish at high temperatures, and as the temperature was lowered, it became pink and superconductive after which it became red and non-superconductive again. It only becomes superconductive at room temperature at a pressure of about 10 000 atmospheric pressures. This is still higher than what we expect from a regular room but dramatically lower than previous experiments.
To measure the Meissner effect, they used a vibrating-sample magnetometer (VSM). Using this method, a sample is placed in a constant magnetic field and moved up and down. Depending on the magnetising properties of the sample, the alternating magnetic field induces a proportional electric current in the pickup coils of the VSM. This allows measuring the magnetic properties of the sample.
Composition of the new material
The way the atoms are arranged in this material is at the heart of why it superconducts. This is why scientists are interested in studying its composition, using different analyses: X-ray diffraction (XRD), Energy Dispersive X-ray spectroscopy (EDX), and Raman spectroscopy.
XRD and EDX use X-rays to study the crystal structure of a material. X-rays are sent in all directions onto a crystalline material. By studying how the X-rays are scattered, information about the elements within, the crystal structure, and lattice spacing can be obtained.
Raman spectroscopy uses laser light to study the material. When a laser is directed onto a material, the scattered light lets us study the vibrational modes of the chemical bonds within the material — which gives information about the different kinds of bonds in a material.
These analyses showed the presence of two distinct hydride compounds — each with a face-centred cubic (fcc) metal sub-lattice but with varying contents of hydrogen and nitrogen.
However, more experiments are needed to determine the exact crystal structure of the material.
How will this affect us?
This research is unlikely to change our lives just yet because all of this still requires extremely expensive laboratory equipment and very high pressure. Moreover, this study is not reproducible by other research groups because some key details of how to make the material are still missing for intellectual property reasons. This is because the research was funded by a company that owns the intellectual property rights.
So what do you think? Are you excited about the future of humankind with the possibility of superconductors? Let me know in the chat below! 👇Also check out this amazing video for more information!