Neutron News | 2021
Review of Principles of Neutron Scattering from Condensed Matter
Abstract
Review of Principles of Neutron Scattering from Condensed Matter, by A. T. Boothroyd, Oxford University Press, Oxford, United Kingdom (2020). Neutron spectroscopy has diversified considerably since the development of the triple-axis spectrometer by Brockhouse at Chalk River Laboratory’s NRX reactor in Canada. Over the past several decades, neutron instruments covering an unprecedented range of frequencies and length scales have been developed at both steadystate reactor and pulsed spallation sources. Many excellent books review the technique including the early book by Squires, the focused and practical account of triple-axis spectroscopy by Shirane, Shapiro, and Tranquada, the more general book by Willis and Carlile, which includes time-of-flight methods, and Sivia’s book on elementary scattering theory, which emphasizes a geometric interpretation. In terms of theoretical accounts, the book by Lovesey is a classic, comprehensive, and lasting reference. Of course, this list of books is far from complete, and there are many important collections of articles and chapters that review a range of topics, often built from workshops or schools, which, regrettably, I do not have space to name or put into context. Given the diversity of neutron resources available today, there is a clear gap in the literature, which has not kept pace with the growth in neutron instrumentation or the analysis techniques applied to them. With a correspondingly diverse user base founded on a range of instruments with disparate capabilities, this gap poses a real problem to the user community. And with new neutron sources and instruments coming online, there has been a strong need for a complete, diverse, and forward-looking reference in the field. Principles of Neutron Scattering from Condensed Matter by Andrew Boothroyd fills this void and provides an important update to the neutron scattering community. The book is self-contained so that a scientist with a knowledge of basic atomic physics can be guided to understanding cross sections, as well as pointed toward the appropriate instrument. It offers examples and problems, allowing the reader to be self-taught in a pedagogical manner. It can also be accessed by scientists at different levels of interest and skills, being easily readable by those with either a more theoretical or practical interest. This book will serve as an excellent textbook and resource in the field for workshops or schools on neutron scattering. The book starts off with an overview of neutron scattering, covering different types of neutron sources and cross sections. This is followed by a general outline of scattering theory including response functions. This part of the book has a nice section on sum rules, and it discusses other properties of the neutron response like detailed balance, linking it with the general properties of response theory. These well-defined features of the neutron scattering cross section make neutron spectroscopy an important probe of condensed matter physics, and it is timely these be reviewed. The book gives a modern description of magnetic spectroscopy applied to several examples, and it discusses the random phase approximation and itinerant magnetism, which is important in the context of iron-based and cuprate superconductivity. This links nicely to the work by Jensen and Mackintosh, which is dedicated to this topic in the context of rare-earth magnetism. It also illustrates an important feature of this book: while it provides a broad coverage of the field that is completely selfcontained, it can also be used as a step to more focused accounts of a particular topic with the book’s complete bibliography providing a guide. The book ends with an overview of practical aspects of neutron scattering that are often overlooked. This includes neutron optics, resolution, extinction, spurions, etc. These are outlined in a clear and concise manner. The appendix of this book is particularly interesting because it provides an in-depth overview of the mathematics and quantum mechanics required for a fuller appreciation of some aspects of scattering theory. This material is often neglected in other books, which then requires the reader to search for the details by trolling through tangential references or topics. Including this in the same book with appropriate references is truly unique and will be appreciated by many readers. It might also serve as a way for neutron scattering to work its way into courses on quantum mechanics or waves. Indeed, it would be a real step forward for the field of neutron scattering if the applications of observables, uncertainty, response theory, etc. were discussed in undergraduate courses as is already done with examples taken from other areas of physics including high-energy and atom optics. This book could help provide such a step. Andrew Boothroyd has done a lasting service to the neutron user community by compiling a reference that is accessible to scientists at all levels. I personally enjoyed reading through it, and I look forward to using it in future research as well as for teaching purposes. Andrew is often complimented for the clarity and thoroughness of his lectures and talks. I think I can speak for everyone when I write that we are incredibly fortunate and grateful to have that in a lasting book that we can access anytime and anywhere.