BCS: 50 Years

BCS: 50 Years , Edited by Leon N. Cooper and , Dmitri Feldman World Scientific, Hackensack, NJ, 2011. $135.00, $65.00 paper (575 pp.). ISBN 978-981-430-464-1, ISBN 978-981-430-465-8 paper

Superconductivity is enjoying a banner period: This year we commemorate the 100th anniversary of its discovery by Heike Kamerlingh Onnes, and in 2007 we celebrated the 50th anniversary of the Bardeen-Cooper-Schrieffer (BCS) theory. Not surprisingly, those occasions have led to renewed interest in the subject and its history; as a result, various books on superconductivity are surely in the offing. An early entry is BCS: 50 Years, a collection of articles put together by Leon Cooper (the “C” in BCS) and Dmitri Feldman. It sets a high standard.

In BCS: 50 Years, the editors have combined historical reflections by many of the principals in the theory’s development and confirmation, reviews of more recent works of fundamental significance, and essays on the broader importance of BCS theory to other physics subfields such as atomic and high-energy physics. As is unavoidable for such books, the contributions vary widely in style and accessibility, but the editors deserve praise for the selection of topics and for enlisting a distinguished set of authors. Present are the voices of John Bardeen, Cooper, and J. Robert Schrieffer and of fellow physics Nobel laureates Philip Anderson, Wolfgang Ketterle, Anthony Leggett, Yoichiro Nambu, Steven Weinberg, and Frank Wilczek.

There are many fine contributions in this book, but for me the most engaging are in the first section, “Historical Perspectives.” Physicists are rigorous in distilling over time the essence of our subject, slowly but surely eliminating the ever-present human drama. In this book, the science and the associated personalities are illustrated by those personally involved in the development of superconductivity theory, culminating in the celebrated BCS theory and its important field-theoretic elaborations. There is even a chapter called “Failed Theories of Superconductivity,” which includes vignettes of many of their inventors that are wonderfully juxtaposed with comments by many of the book’s contributors about what made Bardeen so special as a theorist and a human being.

The essays in the second section—“Fluctuations, Tunneling and Disorder”—address important elaborations of the BCS theory. Of those, one likely to be of broad interest deals with resistance in superconductors from the macroscopic quantum point of view and how disorder can reduce a superconductor’s transition temperature T_c. Another potentially appealing essay discusses pair breaking and the importance of time-reversal symmetry in superconductors. It also explains that, contrary to common misconception, superconductors need not have gaps in the superconducting density of states. Yet another chapter describes the conditions under which an otherwise homogeneous superconductor breaks translational symmetry and forms patterns known as pair density waves. Though the topic of pair density waves has a long theoretical history, it is experiencing a renaissance as the necessary conditions and materials for its occurrence are becoming more commonplace. Also in this section is the story of superconducting quantum interference devices and a description of the multitude of vortex phases possible in the vortex lattice, when thermal fluctuations are important to the process.

The third section—“New Superconductors”—focuses on the materials, including the high-T_c superconductors, and mechanisms of superconductivity. Among the essays is a summary of the success over the past 50 years of BCS and the electron–phonon interaction and its prospect for prediction of new and higher-T_c superconductors going forward. That discussion is juxtaposed appropriately with a discussion of the enlightened empirical search for new and higher-T_csuperconductors. Based on history, the smart money would be to bet on the empiricists over the theorists in the discovery of a new high-T_c superconductor, but there is much present debate on empiricism versus theory, and only time will tell. It’s too bad more of the flavor of that debate is not captured in this book.

“BCS Beyond Superconductivity,” the book’s final section, contains a series of wonderful essays on the impact of the BCS theory outside the traditional boundaries of superconductivity. Superfluid helium-3, trapped fermion gases, and neutron stars make their appearance. How the infusion of ideas from BCS theory—for example, pairing and spontaneous symmetry breaking—impact high-energy physics also is discussed. All students of superconductivity will want to read those essays if only to see the unified portrait of the physics they describe.

BCS: 50 Years is a successful attempt to capture the history of the development of superconductivity theory and its continuing impact. Any person curious about superconductivity will find something in this book to enjoy.