The Sixth State of Matter

by Yuanzheng Mao

When we talk about the topic of states of matter, what things first come to you? Solid? Liquid? Or gas? I guess most people would think of any one of these three, because they are pretty much what we experience with our senses in daily life. For example, when we touch a solid, we usually feel it is hard. If, unfortunately enough, banging into some solid (e.g., a table), we will feel great pain. If we slowly put our hand into a tub of liquid (e.g., water), we will know that the water is wrapping around and changing its shape complementary to our hand. About gas, we may not realise it that much apart from being in windy days. As a matter of fact, on average, molecules in air are moving at and bumping into us at a speed of 500 m/s, [1] more than 10 times faster than a cheetah! [2]

Nevertheless, you may think: are there any more states of matter? Well, the answer is: Absolutely, yes. In fact, there are more than 10 states of matter, and even solid can be classified into different sub-groups by different properties. [3] In this article, I am introducing you what’s termed “the sixth state of matter”—Fermionic condensate. [4]

Physicists have created a successful theory that describes everything they know about matter—the Standard Model. [5] Our matter is made from up quarks, down quarks, and electrons, which are all involved in it. [6] All particles in the Standard Model are divided into two groups—fermions and bosons, according to one of their properties called “spin” (Figure 1) Additionally, other particles that are made up from the particles in the Standard Model, have “spin” too (e.g., atom). In other words, atoms can be grouped into fermions and bosons as well.

 

Figure 1 The particles in the Standard Model. Quarks (green boxes) and leptons (red boxes) are collectively called fermions. The others (purple boxes and blue box) are called bosons. Picture from https://www.sciencefocus.com/science/what-is-the-standard-model/

Usually, in normal life, particles move individually. For instance, molecules in the air keep colliding with each other like billiard balls. [7] But, when atoms (bosons) are cooled down to terrifically low temperature, abnormal things happen. Scientists describe them by quantum mechanics: these atoms don’t act as individuals any more, but work as one big, whole, complete entity, like a “superatom”. [7] [8] This is new state of matter is called “the fifth state of matter”—the Bose-Einstein condensate. [9] In 1995, M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E. Wieman, E. A. Cornell published on Science how they applied laser beams and magnetic fields to cool rubidium-87 atoms (bosons) down to about 170 nanokelvin, which is within 1 Celsius degree away from the limit of low temperature (absolute zero). By doing so, they created the Bose-Einstein condensate. [10] Their revolutionary work finally won C. E. Wieman and E. A. Cornell, together with Wolfgang Ketterle, who made Bose-Einstein condensate out of sodium-23 atoms (bosons), the Nobel Prize in Physics 2001. [7] [11]

After this great breakthrough, people were wondering: “Can we also create something similar to Bose-Einstein condensate out of fermions?” Well, bosons like to stay together to behave as one whole entity, for which reason they can form Bose-Einstein condensate. [12] At this time, a problem occurred: According to Pauli exclusion principle, fermions can’t act as a whole! [12] [13] They have to be alone. However, science always gives people surprise: There is, in fact, a solution, without violating Physics Laws. This was published on Physical Review Letters in 2004, by C. A. Regal, M. Greiner and D. S. Jin. They cooled potassium-40 atoms (fermions) down to nearly absolute zero (around -273 ℃) and then applied a magnetic field to the atoms. By doing so, the atoms match up into pairs. Collectively, each pair behaves like bosons, which in turn gets into a similar state as Bose-Einstein condensate. [12] [14] People call this state where fermions pair up and together behave like bosons “Fermionic condensate”—the sixth state of matter. (Figure 2)

 

Figure 2 False color images of a condensate formed from pairs of fermion potassium atoms. Higher areas indicate a greater density of atoms.—cited from https://web.archive.org/web/20061207131059/http:/www.colorado.edu/news/releases/2004/21.html. This picture is also from this website.

There are many potential applications of the Fermionic condensate. For example, Jin is very optimistic about the development of better superconductor because of her achievement. [12] Superconductor has no electrical resistance [15]—a property of conductor which causes energy loss. With no such resistance, superconductor can reach an incredibly high efficiency. But superconductors now only work at very low temperature. So, if some superconductor working at room temperature is invented, there is very likely to be another revolution to the humans.

 Acknowledgement

I would like to thank my Physics teacher, Mr McLean, who set us some homework to prepare a presentation on materials. Therefore, I was able to get the idea about this article. I also would like to thank my friend, Rukhsar Naguman, who generously offered me many useful resources about Bose-Einstein condensate and Fermionic condensate. Therefore, I was able to develop my knowledge and improve my article.

 References

[1] B. H. Suits (2022), Speed of Sound in Air [online] Last accessed 8 March 2022: https://pages.mtu.edu/~suits/SpeedofSound.html

[2] Wikipedia (2022), Cheetah [online] Last accessed 8 March 2022: https://en.wikipedia.org/wiki/Cheetah

[3] Wikipedia (2022), List of States of matter [online] Last accessed 8 March 2022: https://en.wikipedia.org/wiki/List_of_states_of_matter

[4] David Whitehouse (2004), New form of matter created in lab [online] Last accessed 8 March 2022: http://news.bbc.co.uk/1/hi/sci/tech/3441643.stm

[5] Robert Oerter (2006), The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics, New York, Plume

[6] The Royal Institution (2017), Quantum Fields: The Real Building Blocks of the Universe – with David Tong [online] Last accessed 8 March 2022: https://www.youtube.com/watch?v=zNVQfWC_evg&t=1582s

[7] Nobel Prize Outreach AB 2022 (2001), Information for the Public [online] Last accessed 8 March 2022: https://www.nobelprize.org/prizes/physics/2001/popular-information/

[8] Sidney Perkowitz (2008), Bose-Einstein condensate [online] Last accessed 8 March 2022: https://www.britannica.com/science/Bose-Einstein-condensate

[9] Charles Q. Choi (2020), Scientists create exotic, fifth state of matter on space station to explore the quantum world [online] Last accessed 8 March 2022: https://www.space.com/exotic-matter-quantum-world-on-space-station.html

[10] Anderson, M. H., et al. “Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor.” Science, vol. 269, no. 5221, American Association for the Advancement of Science, 1995, pp. 198–201, http://www.jstor.org/stable/2888436.

[11] K. B. Davis, et al. (1995), ‘Bose-Einstein Condensation in a Gas of Sodium Atoms’, Phys. Rev. Lett., vol. 75, no. 22, pp. 3969--3973

[12] University of Colorado at Boulder (2004), NIST/University of Colorado Scientists Create New Form of Matter: A Fermionic Condensate [online] Last accessed 8 March 2022: https://web.archive.org/web/20061207131059/http://www.colorado.edu/news/releases/2004/21.html

[13] Wikipedia (2022), Pauli exclusion principle [online] Last accessed 8 March 2022: https://en.wikipedia.org/wiki/Pauli_exclusion_principle

[14] C. A. Regal, et al. ‘Observation of Resonance Condensation of Fermionic Atom Pairs’, Phys. Rev Lett., vol. 92, no. 4, pp. 040403

[15] Paul Sutter (2021), What is a superconductor? [online] Last accessed 8 March2022: https://www.livescience.com/superconductor