New Superconductors: From Granular to High T_c

New Superconductors: From Granular to High T _c , Guy Deutscher , World Scientific, Hackensack, NJ, 2006. $52.00 (222 pp.). ISBN 978-981-02-3089-0

Superconductivity, a spectacular phenomenon known since 1911, has too many strands to be covered in any one book. This is especially true since the groundbreaking 1986 discovery by J. Georg Bednorz and K. Alexander Müller of high-T _c superconductivity in a novel class of oxides. The challenge of understanding the physical mechanism for high-T _c and recognizing the significant opportunities for technological applications of high-T _c materials has, however, prompted an audience willing to forgo comprehensive treatments for useful insights and alternative approaches. Those readers should be served well by Guy Deutscher’s New Superconductors: From Granular to High T_c.

Deutscher correctly recognizes that high-T _c superconductivity can best be understood when compared against the backdrop of conventional superconductivity, as described by the Bardeen-Cooper-Schrieffer (BCS) theory. The book is thus launched with a discussion of the Landau criterion for the critical velocity of a superfluid. The discussion evolves into a clearly articulated comparison of the two modes of pair condensation: BCS, which takes place in conventional superconductors, versus Bose–Einstein (BE), which possibly occurs in the underdoped regime of the high-T _c superconductors.

Throughout the book Deutscher effectively uses the distinctions between BCS and BE condensation to highlight the link, anticipated by the book’s title, between granular and high-T _c superconductivity. In the granular variety, regions of superconductivity in a material are spatially separated from one another. Deutscher, a professor in the school of physics and astronomy at Tel Aviv University in Israel, is eminently qualified to make the connection. He has had a productive research career focused on granular superconductivity and, more recently, on the high-T _c cuprates. Deutscher’s presentation of the similarities and differences implied by the subtitle is set out in the first half of the book and is persuasive for readers who carefully follow the text. For example, the separation of temperature scales describing the respective onsets of intra- and inter-grain superconductivity is argued to be analogous to the high-T _c behavior in which pairs form at a higher temperature and then condense at a lower temperature.

In another example, small coherence volumes in high-T _c superconductors are compared to small grains in low-T _c superconductors; both dramatically enhance the effects of fluctuations, which are then linked to the phase diagrams of granular and high-T _c materials. Tuning the respective control parameters—intergrain coupling and carrier doping—to drive each system from a metal toward an insulating state leads to increased T _c in both systems. A compact treatment of Coulomb screening offers possible reasons for the increase in T _c and thereby sets the stage for a later, more detailed chapter on high-T _c mechanisms that rely, paradoxically, on enhanced Coulomb interactions. The chapter’s message is double-loaded, convincing, and instructional.

The second part of the book explores in more detail the unique properties of the cuprates, such as structure, doping, transport, enhanced density of states, pseudogaps, and gap symmetry. Standalone chapters on the basics of vortices and vortex-lattice melting facilitate a smooth transition to the final two chapters. Those two chapters address the connection between fundamentals and applications and conclude with a rather detailed discussion of the relative advantages of magnet wires and tapes made of yttrium-barium-copper-oxide (YBCO) and the more two-dimensional bismuthates. The discussion on applications provides an opportunity for the author to speculate on how further fundamental understanding might increase the scope and impact of future applications. Graduate students and experts alike will benefit from the author’s insights into fundamental questions addressing the limits of high T _c, the nature of unconventional pairing, the limits to critical currents, the relevance of a BCS to BE crossover, and the problems and opportunities associated with short coherence lengths. A particularly interesting conjecture on the relationship of inhomogeneous clusters of hole-rich regions to a high-T _c mechanism returns appropriately to the recurrent theme of connecting granular and high-T _c behavior.

Unfortunately, poor editing is a major blemish on Deutscher’s book. Critical figures—for example, figure 1.2—are mislabeled, figure captions are sometimes irrelevant and misleading, equations are mistyped and incorrectly referenced in the text, and grammar errors give the impression that copy-editing was bypassed. Nevertheless, readers of New Superconductors will benefit from the unusual and compelling insights of a researcher who has thought deeply about both granular and high-T _c superconductors. I recommend it as a self-study guide for students, instructors, and researchers who are looking for understandable and crisp material on the potential and promise of high-T _c superconductors.