What’s condensed matter physics?

Many technologies and devices that have revolutionized the way we live, work, and communicate, such as tablets, latptops, and smartphones, would not be possible without groundbreaking discoveries in condensed matter physics.

If you have a general interest in science, and I guess you do as you’re reading this blog, you’ve probably heard of astrophysics and particle physics — thanks to documentaries, movies, and TV shows, such as Star Trek or The Big Bang Theory. Condensed matter physics is another subfield of physics, whose discoveries have had a huge and possibly even more direct impact on our lives, even though most people are unaware of this fascinating discipline.

Roughly speaking, condensed matter physics is about understanding the physical matter that surrounds us. About understanding its properties and the phenomena arising from them. These properties come in an incredible variety. Just to name a few: Matter can exist in various phases, such as the solids, liquids, or gases we know from our everyday lives. Matter has different colors, shapes, and textures. Some materials are transparent, others don’t let any light through, others reflect light. Some materials are electrical conductors, others are insulating, others can even carry electrical currents without any resistance (so-called superconductors). Some materials are permanent magnets, others can be magnetized, others don’t seem to have any magnetism at all. Matter can even form complex organic structures eventually leading to something we call life. All these diverse and fascinating properties arise, even though matter is made up of only a small number of different building blocks called atoms.

Left: ordinary pencil with a core made of graphite. Right: jewelry with diamonds. Both graphite and diamond are made of the exact same element, carbon, but have very different properties. The reason for this lies in the different arrangement of their carbon atoms. In graphite, the carbon atoms form weakly coupled sheets that stick together. In diamond, the carbon atoms arrange themselves into a more rigid three-dimensional lattice. (first photo by madca7 from Wikimedia Commons, distributed under a GNU FDL license; second photo from Wikimedia Commons, distributed under a CC BY-SA 4.0 license)

These building blocks are tabulated in the periodic table of elements you probably know from school. It contains chemical elements such as hydrogen, carbon, iron, or gold. 94 of these elements occur naturally, but only 80 of them are actually stable. Uranium, for instance, is unstable, because it decays into other elements making it radioactive. This raises an obvious question: How can so few building blocks lead to the enormous diversity of matter we experience in our everyday lives? Even materials made up of the same elements can have very different properties. For example, take diamond and graphite - the stuff that makes your pencil write. Both are made up of only a single element: carbon. Yet, diamonds are transparent and one of the hardest materials on earth, whereas graphite is opaque and brittle.

Why is that?

A simple and rather general answer to this question is provided by the principle of emergence, which is one of the guiding principles in condensed matter physics: Matter is more than just the sum of its parts but rather the result of their complex interplay. In condensed matter physics, in particular when dealing with the physics of solids (also known as solid state physics), we are typically faced with very large numbers of atoms that arrange themselves in certain spatial patterns. And by very large I mean millions of millions of millions of atoms. That’s roughly how many atoms fit into a grain of salt. As the atoms come close together in this arrangement, they start to collectively interact with each other. The exact details depend on many factors, such as the types of atoms involved or external conditions like temperature or pressure. This gives rise to emergent and oftentimes unexpected phenomena, such as magnetism, superconductivity, and many, many more.

Levitation of a magnet above a superconductor (photo by Mai-Linh Doan from Wikimedia Commons, distributed under a CC BY-SA 2.5 license).

It’s this intricate interplay that’s so fascinating about condensed matter physics. Understanding it makes it possible to manipulate matter in a controlled way and even design new materials with tailored properties. Also, as I already hinted upon at the beginning of this post, the discoveries in this field have led to numerous technological innovations. For instance, you wouldn’t be reading this blog without the discovery of the field-effect transistor, which all modern computers are based on. The miniaturization of magnetic disk drives was enabled by the discovery of the giant magnetoresistance effect. Modern flat screens, as used in phones and TVs, benefitted a lot from the discovery of organic semiconductors and the development of organic light-emitting diodes (OLEDs). In the future, our society might see the next revolution with the advent of quantum computers, which might be able to solve certain tasks even the fastest conventional supercomputers would need thousands or even millions of years for.

This was just a brief glimpse into the realm of condensed matter physics. In the following blog posts, I will take you deeper into this fascinating field. First up, I will tell you more about the previously mentioned spatial patterns atoms form in solid matter — better known as crystals.

Stay tuned for my next post and thanks for reading!

This popular-science blog is about a fascinating link between the physics of condensed matter and a mathematical discipline called topology. I write about the basic concepts and about my own research revolving around this topic in an accessible language.

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Alexander Lau

Alexander Lau

Theoretical physicist and science enthusiast

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