Author: ZapperZ (on physicsforums.com)

Consider the fact that when most bright-eyed physics majors in their first year entering a university, they are either not aware, or hardly know anything about a field of physics known as condensed matter. Yet, if they go on to receive their Ph.D in physics, there is a 55% to 60% chance that they will be graduating with a specialization in such a field! It is estimated by various professional physics organizations that roughly 50% of all practicing physicists are in condensed matter physics/material science. It is certainly the largest and most dominant division under the wing of the American Physical Society. It also produces the largest amount of peer-reviewed publications.

So what is "Condensed Matter Physics"? Condensed matter (CM) is the study of matter. It is not the study of atoms, molecules, and particles in isolation, but rather it is the study of atoms, molecules, and particles when there's a gazillion of them AND they are also interacting with each other. This is what goes on in solids, and very often in certain types of liquids and gasses also. Solid State physics is a large part of CM. This means that CM covers a huge range of phenomena, ranging from the properties of metals, semiconductors, insulators, to superconductivity, to magnetism, etc. It is because it is such a huge field that CM is the only area of physics with two separate sections in the Physical Review Letters. It is also the only subject area of the Physical Review journals series that produces FOUR volumes per month (Physical Review B).

So why is CM so huge and so important? The most obvious reason is that this is the one area of physics that produces direct practical applications. All of the advances in modern electronics came out of our understanding of the properties of materials and our ability to fabricate, manipulate and control them. So when someone asks if physics has any practical applications, chances are he/she isn't aware of this area of physics.

However, the non-obvious reason that is equally important is that the advancements and discoveries coming out of CM have important and wide-ranging implications throughout physics. At the most fundamental level, CM studies how things interact with each other. This knowledge transcends CM physics and is important in any field of physics. Important discoveries made by Phil Anderson on the broken gauge symmetries are now common principles used in field theories and particle physics. The Higgs mechanism itself came out of CM. Thus, the progress in the theoretical understanding of CM systems have wide-ranging impact on practically all of physics.

The third reason why CM is so important is because this is the area of physics that consistently produces a description of a phenomenon with some of the highest degree of certainty. Because of the ability to fabricate and control a measurement, CM phenomena can often be tested repeatedly, often by simply changing one parameter at a time. This allows for some of the most reproducible results anywhere in physics, giving it the highest degree of certainty. In fact, the value of physical constants such as the Planck constant "h" and the elementary charge "e" are determined from values measured from CM physics experiments. CM experiments also produce some of the most convincing evidence for the validity of quantum mechanics and special relativity.

There are many exciting discoveries and phenomena left to be studied in CM, which leads the study of many-body phenomena. I highly recommend readin Piers Coleman recent article on this, which should also give a flavor of the importance of such a field. I can only hope that many incomming students would at least be aware of the wide horizon that is out there, and that physics isn't just some esoteric area of study that is confined only to nuclear, particle, or even (ugh) string theory.

http://arxiv.org/abs/cond-mat/0307004

Zz.