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Superconducting Metallic Hydrogen

By Maritha Wang

For decades, the scientific community has quietly held its breath in wait of a discovery that could change the landscape of electronics as we know it: the discovery of materials that exhibit superconductivity at room temperature. Superconductivity is a phenomenon in which a substance exhibits no electrical resistance, enabling electrical systems to reach new levels of efficiency. Implications include incredibly powerful electromagnets used in particle accelerators, magnetic resonance imaging (MRI), and flotation of transport systems such as maglev trains.

Since the discovery of superconductivity in 1911 by Heike Kamerlingh Onnes studying mercury at cryogenic temperatures, scientists have been trying to produce superconducting materials or coax materials into a superconducting state with limited success. Mercury, when cooled below 4.1 Kelvin (K), is able to conduct with zero electrical resistance. For lead, this critical temperature occurs at about 7.2 K. Materials with critical temperatures in the 120 K range have received much attention because they are able to maintain superconductivity if cooled with liquid nitrogen, a relatively easy-to-acquire substance. Keeping these materials at such low temperatures for extended periods of time, however, remains difficult and takes a lot of energy, and has been a giant road block for the conventional use of such materials.

In exciting new research published in Science in January 2017, Harvard scientists Isaac F. Silvera and Ranga P. Dias discuss their apparent success in producing metallic hydrogen after decades of theorizing and attempted experiments. Hydrogen atoms were compressed in a diamond anvil at high pressure (495 GPa, which converts to 71.1 million pounds per square inch), producing a sample measuring approximately 1.5 by 10 micrometers (about a fifth the width of a human hair). Unfortunately, the sample was lost in late February when the diamond anvil in which it was contained was damaged when the sample was being measured by a laser. It remains unclear whether the sample is simply lost somewhere among the equipment or has returned to its gaseous state. Either way, if Silvera and Dias manage to make another sample, the implications are potentially far- and wide-reaching.

Schematic of creation of atomic metallic hydrogen. Source: ExtremeTech. Reproduced under Creative Commons 2.0.

Most notably, this new form of hydrogen—a solid—seems to have the potential to be stable at room temperature and thus could possibly serve as a room temperature and high temperature superconductor, which would have important implications for energy and rocketry. Before its loss, the metallic hydrogen sample was kept under high pressure (495 GPa) and low temperature (15 K). Data taken regarding reflectance of the sample was in agreement with theoretical calculations of properties of metallic hydrogen. Additionally, if the metallic hydrogen could become liquid when removed from its laboratory-controlled low temperature and high pressure conditions, it may theoretically display superfluidity, the property that enables a substance to flow without friction.

If room temperature superconductors were to become usable in everyday applications, the impact would span a multitude of applications and industries. In Magnetic Resonance Imaging (MRI), which is used extensively in healthcare, superconductors are used to increase the strength and uniformity of the magnetic field, leading to clearer images. A common superconductor used for MRIs is neodymium, which is able to reach a magnetic field about 8 times stronger than that of a typical permanent magnet. However, neodymium must be kept at about 4 K to exhibit superconductivity, and maintaining this low temperature requires a lot of energy. Implementing a room temperature superconductor like metallic hydrogen would drastically reduce the energy costs of running MRI scans, thus leading to imaging that is incredibly more efficient and cost-effective.

Particle accelerators also utilize superconductors to create stronger magnetic fields, allowing for more powerful and compact accelerators that are cheaper to use. Similarly, flotation of transport systems requires strong magnetic fields that are achievable through the use of superconductors. Room temperature superconductors give rise to powerful magnetic fields like those we have today, but without the huge energy input needed to meet the temperature requirements for most currently known superconducting materials.

The loss of the metallic hydrogen sample means that a new sample must be created before testing can be done. Furthermore, there has been some skepticism over whether the sample Silvera and Dias observed really was metallic hydrogen. Some think that they may have been hasty in concluding this without first running a full set of tests. However, even if Silvera and Dias are able to replicate their experiment and prove the identity of their substance, many other challenges remain in the exploration and potential application of metallic hydrogen in systems. It first needs to be subjected to a variety of conditions to assess its stability. If it proves stable, then further investigations of its superconducting properties must be conducted. And if all of these investigations prove promising, there still remains the question of how feasible its large-scale production will be. Nevertheless, the continued push in superconductor research is promising and has the potential to have wide and lasting effects on many industries, and consequently, everyday life as a whole.

References

1. R. Dias, I. F. Silvera. 2017. Observation of the Wigner-Huntington transition to metallic hydrogen. Science. http://science.sciencemag.org/content/early/2017/01/25/science.aal1579.

2. Superconductivity. HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/scond.html.

3. R. Whitwam. 2017. The only sample of metallic hydrogen on Earth has vanished. ExtremeTech. https://www.extremetech.com/extreme/244922-sample-metallic-hydrogen-earth-vanished.

4. Accelerators for Particle Physics. Le Centre national de la recherche scientifique (CNRS), Société Française de Physique 

(SFP), Le Triangle de la Physique. http://www.supraconductivite.fr/en/index.php?p=applications-accelerateurs.

5. K. Kose, T. Haishi . 2011. High Resolution NMR imaging using a high field yokeless permanent magnet. Magnetic Resonance in Medical Sciences. https://www.ncbi.nlm.nih.gov/pubmed/21959998.

6. D. Castelvecchi. 2017. Physicists doubt bold report of metallic hydrogen. Nature | News. http://www.nature.com/news/physicists-doubt-bold-report-of-metallic-hydrogen-1.21379.

Maritha Wang is a first-year student at the University of Chicago majoring in Chemistry and Molecular Engineering. She is interested in exploring research in a variety of fields including chemistry, materials science, and medicine.

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