What Is Superconductivity?

Hi everybody, my name is Jim Bray.  You may recognize me from the Stump the Scientist series.  However, today I am not answering questions but offering out my opinion on the topic of superconductivity.  I have a Ph.D. in theoretical condensed matter physics, with a focus on superconductivity, taken under Professor John Bardeen at the University of Illinois.  I have been working on various aspects of superconductivity (among other things) at GE Global Research for around 35 years.

Superconductivity is a particularly appropriate topic in 2011, since this is the 100th anniversary of the discovery of superconductivity (SC) in 1911 by Kamerlingh Onnes. By the way, he won a Nobel Prize for this, and this was the first of 5 Nobel Prizes that have been awarded in this area, perhaps the most for any specific, narrow area of condensed-matter physics. Hence, we can see a first reason for studying this area: it is rewarding intellectually and academically (to say nothing of the prize money). But why is this the case? The answer to this will reveal more reasons for studying it.

Superconductivity is usually described most simply as the ability of a material to conduct electricity with zero resistance (i.e., a perfect conductor). This is true, although it is also true that SC has other distinguishing properties such as the ability to exclude magnetic fields (the so-called Meissner Effect). All known superconductors have to be made very cold before they will enter the superconductive state with perfect conductivity. This perfect conductivity means that if you have a superconductor in a closed loop which carries current around the loop, it will continue to carry it forever without loss. This sounds like perpetual motion, and it is in a way; it happens because of the properties of quantum mechanics.

Superconductivity is an example of a quantum phenomenon at a macroscopic scale. I’ll dissect what this sentence means.  Quantum theory describes how our universe works, but it normally makes predictions which are critical only at very small scales, such as for atoms. This theory was developed in the early 20th century, mostly after superconductivity was discovered. Many scientists tried to describe how superconductivity works before quantum theory was fully available, and they all failed because it turns out that quantum theory is required to explain superconductivity. It took until 1957 for John Bardeen, Leon Cooper, and Robert Schrieffer to use quantum theory to explain how superconductors work (called the BCS theory), and, not surprisingly, they won the Nobel Prize for this. Very rarely, the effects of quantum theory become visible on a large (macroscopic) scale where we can observe them easily. The perfect conductivity of superconductors is an example of this and is another reason technologists have been drawn to study superconductivity.  If you recall from the first paragraph, I studied under one of these men, John Bardeen, for my PhD and it was an honor to do so.

Another reason for studying superconductivity is that it requires a number of technical disciplines to use it usefully. I have already mentioned the physics and the fact that superconductors  must be kept very cold, which brings in the technologies of cryogenics and thermal engineering. Since superconductors carry electric current in all it applications, electrical engineering is very important to connect the SC properly to its surroundings, including the other electrical equipment with which it must function. Superconductors are often used to produce electromagnets, and these magnets produce forces that must be properly accommodated, requiring many skills of mechanical engineering. Besides perfecting the SC material itself, many material combinations are required to insulate and protect the SC and its surrounding environment, and this requires expertise from materials science and technology and chemistry. The necessary interaction of all these disciplines provides much stimulation and advancement of breadth of expertise for those studying superconductivity.

Another reason to study superconductivity is the challenge and opportunity; it is far from being a finished field. The details of superconductivity physics are so complex that new materials continue to appear that require additional knowledge to determine the details of their functioning. The latest big example of this was the discovery of HTS (high temperature superconductors) in 1986 by Bednorz and Muller, and this also won the Nobel Prize. This class of superconductor operates at temperatures that go above liquid nitrogen (at 77 Kelvin), which is still quite cold but much above the older superconductors. The details of how HTS achieve the superconducting state is still the subject of theoretical work in physics; there are many complex parameters in superconductivity theory, and the BCS theory  left open many such details. Other new superconductors have also been discovered which beg for descriptions of the details of their superconducting properties. So it is likely that further Nobel Prizes await those who can either explain the new puzzles being offered by nature in superconductivity or find yet new important superconductive materials.

My personal final reason to stud superconductivity is that it is useful to mankind. Several businesses have arisen because of the abilities made possible by superconductors. The largest is MRI (magnetic resonance imaging). The large magnets in MRI systems are superconductive because they are very difficult to make economically any other way. The voltage standards of most countries are based on superconductive devices. Superconductor filters have been employed in thousands of cellphone basestations. Material characterization Nuclear Magnetic Resonance mostly uses SC magnets. Many electromagnets for research (such as in “atom smashers”) are superconductors as well.

I think that you will find that those within the field are extremely passionate about the technology and excited about the prospect of what we have yet to discover about superconductivity.  For those of you out there who are also doing research involving superconductors… why did you enter into this field and what are your favorite things about studying superconductivity?

If you are interested, please click here to find out information on the New York State Superconductor Technology Summit 2011 that is in honor of the 100th anniversary of superconductivity and the local state contributions.

1 Comment

  1. Sebastian A

    Interesting to read about SC and its applications, its challenges. 🙂